Application Note 54
March 1993
Power Conversion from Milliamps to Amps at Ultra-High
Efficiency (Up to 95%)
Dimitry Goder
Randy Flatness
INTRODUCTION
High efficiency is frequently the main goal for power
supplies in portable computers and hand-held equipment.
Efficient converters are necessary in these applications to
minimize power drain on the input source (batteries, etc.)
and heat buildup in the power components, allowing for
smaller, lighter, and longer-lived systems. Power conversion efficiency must be in the 90% range in order to meet
these goals. This application note features power supply
circuits that satisfy these design requirements and attain
high efficiency over a wide operating range.
The recent development of the LTC®1142, LTC1143,
LTC1147, LTC1148, and LTC1149 makes ultra-high efficiency conversion possible. In addition, the LTC1148,
LTC1149, and LTC1142 are synchronous switching regulators, achieving high efficiency conversion at output
currents in excess of 10A. These controllers feature a
current mode architecture that has automatic Burst
ModeTM operation at low currents. This technology makes
90% efficiencies possible at output currents as low as
10mA, maximizing battery life while a product is in sleep
or standby mode.
These ultra-high efficiency converters also implement
constant off-time architecture, fully synchronous switching and low dropout regulation. All these features make
this series of converters a really excellent choice for a vast
variety of applications.
Achieving high efficiency is one of the primary goals of
switching regulator design. Every application circuit shown
in this note includes detailed efficiency graphs. Almost all of
the magnetic parts used in the circuits are standard products, available off-the-shelf from various manufacturers.
and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
AN54-1
Application Note 54
TABLE OF CONTENTS
Buck
LTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology ................................................................ Figure 1
LTC1148: (5V-14V to 5V/2A) Buck Converter .................................................................................................................. Figure 2
LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology...................................... Figure 3
LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology ............................................................. Figure 4
LTC1148: (4V-14V to 3.3V/2A) Buck Converter with Surface Mount Technology ............................................................. Figure 5
LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter ..................................................................................... Figure 6
LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter .................................................................................... Figure 7
LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter ........................................................................................... Figure 8
LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs ................ Figure 9
LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter ....................................................................................... Figure 10
LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter ........................................................................................ Figure 11
LTC1149: (16VRMS to 13.8/10A) Buck Converter ........................................................................................................... Figure 12
LTC1149: (32VRMS to 27.6V/5A) Buck Converter ........................................................................................................... Figure 13
LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology .............................................................. Figure 14
LTC1147: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology ........................................................... Figure 15
LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology .......................................................... Figure 16
LTC1148: (10V-14V to 5V/10A) High Current Buck Convert .......................................................................................... Figure 17
LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter ................................................................... Figure 18
LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter ................................................................. Figure 19
LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter ............................................................... Figure 20
LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter ................................................................................ Figure 26
LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter ................................................................................ Figure 27
LTC1148HV-3.3 (4V-18V to 3.3V/1A) High Voltage Buck Converter .............................................................................. Figure 28
LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter ............................................................................... Figure 29
LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A) Triple Output Buck Converter ...................................................... Figure 30
LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter ............................ Figure 31
Single LTC1149: Dual Output Buck Converter ............................................................................................................... Figure 35
LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter ................................................................................ Figure 36
LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter......................................................................... Figure 37
AN54-3
AN54-4
AN54-5
AN54-6
AN54-7
AN54-8
AN54-9
AN54-10
AN54-11
AN54-12
AN54-13
AN54-14
AN54-15
AN54-16
AN54-17
AN54-18
AN54-19
AN54-20
AN54-21
AN54-22
AN54-28
AN54-29
AN54-30
AN54-31
AN54-32
AN54-34
AN54-38
AN54-39
AN54-40
Buck-Boost and Inverting Topologies
LTC1148: (4V-14V to 5V/1A) SEPIC Converter .............................................................................................................. Figure 21
LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter ................................................................................. Figure 22
LTC1148: (4V-10V to – 5V/1A) Positive-to-Negative Converter ...................................................................................... Figure 23
LTC1148: (5V-12V to –15V/0.5A) Buck-Boost Converter .............................................................................................. Figure 24
AN54-23
AN54-24
AN54-25
AN54-26
Boost
LTC1148: (2V-5V to 5V/1A) Boost Converter ................................................................................................................. Figure 25
AN54-27
Battery Charging Circuits
LTC1148: High Efficiency Charger Circuit ...................................................................................................................... Figure 32
LTC1148: High Voltage Charger Circuit ......................................................................................................................... Figure 33
LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger ......................................... Figure 34
AN54-35
AN54-36
AN54-37
Appendix A
Topics of Common Interest ...........................................................................................................................................................
AN54-40
Appendix B
Suggested Manufacturers .............................................................................................................................................................
AN54-42
AN54-2
Application Note 54
LTC1148: (5V-14V to 5V/1A) Buck Converter with
Surface Mount Technology
A basic LTC1148 application is shown in Figure 1A. This is
a conventional step-down converter that provides 5V output at 1A maximum output current. All the components
used are surface mounted and no heat sink is required.
During Q1 on-time, inductor L1's current is sensed by R2
and monitored by an internal current sensing comparator.
To filter out noise from the current sense waveform, C6 is
added to the circuit. When the current ramp reaches a
preset value, Q1 is turned off, and a clamp diode D1 starts
conducting for a short period of time, until the internal
control logic senses that Q1 is completely off. Then
NDRIVE output goes high turning Q2 on, which shorts out
D1. This provides synchronous rectification and significantly reduces conduction losses during Q1’s off-time.
This regulator has a constant off-time defined by the timing
capacitor C5. To control the output, on-time is varied,
changing the operating frequency and therefore, the duty
cycle. If the input voltage is reduced, frequency decreases
keeping output voltage at the same level. Q1’s on-time
stretches to infinity with low input voltage, providing 100%
duty cycle and very low dropout. Under dropout conditions, the output voltage follows the input, less any resistive losses in Q1, L1 and R2.
Under conditions of light output currents, the regulator
enters Burst Mode operation to ensure high efficiency.
Continuous operation is interrupted by an internal voltage
sensing comparator with built-in hysteresis. in this mode
both Q1 and Q2 are turned off and the comparator monitors
decreasing output voltage. When the output capacitor
discharges below a fixed threshold, operation resumes for
a short period of time bringing the output voltage back to
normal. Then the regulator shuts down again conserving
quiescent current. Under Burst Mode operation the output
ripple is typically 50mV as set by the hysteresis in the
comparator.
+
VIN
5V TO 14V
C3
22µF × 2
25V
3
+
C1
1µF
C2
0.1µF
VIN
10
PDRIVE
1
Q1
Si9430DY
SHUTDOWN
L1
1
4
LTC1148-5
6
SENSE –
R1
1k
4
C4
3300pF
X7R
C5
390pF
NPO
CT
NDRIVE
SGND
11
C1
C3
C7
Q1
Q2
D1
3
R2
0.1Ω
5V
1A
100µH
SENSE +
ITH
2
8
7
C6
0.01µF
+
14
PGND
Q2
Si9410DY
D1
MBRS140T3
C7
220µF
10V
12
(Ta)
AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A
AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
MOTOROLA SCHOTTKY VBR = 40V
R2 KRL SP-1/2-A1-0R100J Pd = 0.75W
L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ® CORE
AN54 • F01A
ALL OTHER CAPACITORS ARE CERAMIC
QUIESCENT CURRENT = 180µA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 200mA
Figure 1A. LTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology
Kool Mµ is a registered trademark of Magnetics, Inc.
AN54-3
Application Note 54
Figure 1B shows efficiency versus output current for three
different input voltages. Generally speaking, efficiency
drops as a function of input voltage due to gate charge
losses and LTC1148 DC bias current. The curves converge
at maximum output current as these losses become less
significant.
100
VIN = 6V
EFFICIENCY (%)
90
VIN = 10V
VIN = 14V
80
70
60
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
LTC1148: (5V-14V to 5V/2A) Buck Converter
A step-down regulator with 2A output current capability is
shown in Figure 2A. To provide higher output power levels
the sense resistor value is decreased, thus increasing the
current limit. This also increases maximum allowable
ripple current in the inductor, so its value can be reduced.
Note that timing capacitor C5 is changed to optimize
performance for a standard inductor value. In this Figure
C7 consists of two parallel capacitors ensuring minimum
capacitance requirement for all conditions. A circuit board
has been laid out for this circuit and has subsequently
been thoroughly tested under full operating conditions
and optimized for mass production requirements. A Gerber file for the board is available upon request.
1
AN54 • F01B
Figure 1B. LTC1148: (5V-14V to 5V/1A) Buck Converter
Measured Efficiency
VIN
5V TO 14V
+
+
C2
0.1µF
C1
1µF
3
VIN
10
PDRIVE
1
Q1
Si9430DY
SHUTDOWN
C3
22µF × 3
25V
L1
62µH
R2
0.05Ω
5V
2A
LTC1148-5
6
SENSE –
R1
1k
C4
3300pF
X7R
C1
C3
C7
Q1
Q2
D1
R2
L1
SENSE +
ITH
4
C5
470pF
NPO
CT
SGND
11
NDRIVE
PGND
8
7
C6
0.01µF
+
14
Q2
Si9410DY
D1
MBRS140T3
12
(Ta)
AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A
AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
MOTOROLA SCHOTTKY VBR = 40V
KRL SL- 1-C1-0R050J Pd = 1W
COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE (THROUGH HOLE)
QUIESCENT CURRENT = 180µA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 400mA
ALL OTHER CAPACITORS ARE CERAMIC
AN54 • F02A
Figure 2A. LTC1148: (5V-14V to 5V/2A) Buck Converter
AN54-4
C7
220µF × 2
10V
Application Note 54
100
LTC1148: (5V-14V to 5V/2A) High Frequency Buck
Converter with Surface Mount Technology
VIN = 6V
EFFICIENCY (%)
90
VIN = 10V
Figure 3A presents essentially the same circuit as Figure
2A, but implementing changes to operate at a higher
frequency. Timing capacitor C5 is reduced to achieve
higher switching rate. This approach allows the use of a
smaller value inductor with surface mount technology,
resulting in a more compact design.
VIN = 14V
80
70
60
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
2
AN54 • F02B
Figure 2B. LTC1148: (5V-14V to 5V/2A) Buck Converter
Measured Efficiency
VIN
5V TO
14V
+
+
C2
0.1µF
C1
1µF
3
VIN
10
C3
22µF × 3
25V
PDRIVE
1
Q1
Si9430DY
SHUTDOWN
1
4
6
C1
C3
C7
Q1
Q2
D1
R2
L1
LTC1148-5
SENSE +
SENSE –
R1
1k
C4
3300pF
X7R
ITH
4
C5
220pF
NPO
CT
SGND
11
NDRIVE
PGND
L1
33µH
2
3
R2
0.05Ω
5V
2A
8
7
C6
0.01µF
+
14
Q2
Si9410DY
D1
MBRS140T3
C7
220µF × 2
10V
12
(Ta)
AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A
AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
MOTOROLA SCHOTTKY VBR = 40V
KRL SL-1-C1-0R050J Pd = 1W
COILTRONICS CTX33-4 DCR = 0.06Ω Kool Mµ CORE
QUIESCENT CURRENT = 180µA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 400mA
ALL OTHER CAPACITORS ARE CERAMIC
AN54 • F03A
Figure 3A. LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology
AN54-5
Application Note 54
Let us compare efficiency graphs in Figures 2B and 3B.
Gate charge losses are directly proportional to operating
frequency, and as a result the efficiency of Figure 3A is
100
VIN = 6V
EFFICIENCY (%)
90
VIN = 10V
80
decreased. However, the effect is most noticeable at high
input voltages and low currents. At maximum load I2R
losses dominate so that the regulator performance varies
only slightly. These two circuits illustrate the fact that best
overall efficiency is reached at moderate frequencies. They
represent a nice example of compromising between regulator compactness and efficiency.
LTC1148: (4V-14V to 3.3V) Buck Converters with
Surface Mount Technology
VIN = 14V
70
Figures 4A and 5A show application circuits for the
LTC1148-3.3 which provides a fixed 3.3V output. The
circuits deliver 1A and 2A output currents, and use exactly
the same circuit configuration and component values as
Figures 1A and 2A. Even though the LTC1148 can achieve
low dropout, the minimum input voltage is limited to 4V to
meet requirements for power MOSFET gate drive, and to
ensure proper operation of the LTC1148 internal circuitry.
60
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
2
AN54 • F03B
Figure 3B. LTC1148: (5V-14V to 5V/2A) High Frequency
Buck Converter Measured Efficiency
VIN
4V TO 14V
+
+
C1
1µF
C2
0.1µF
3
VIN
10
C3
22µF × 2
25V
PDRIVE
1
Q1
Si9430DY
SHUTDOWN
1
4
6
LTC1148-3.3
SENSE +
SENSE –
R1
1k
4
C4
3300pF
X7R
C1
C3
C7
Q1
Q2
D1
R2
L1
ITH
C5
560pF
NPO
CT
SGND
11
NDRIVE
PGND
L1
100µH
2
3
R2
0.1Ω
8
7
C6
0.01µF
+
14
Q2
Si9410DY
D1
MBRS140T3
C7
220µF
10V
12
(Ta)
AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A
AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
MOTOROLA SCHOTTKY VBR = 40V
KRL SP-1/2-A1-0R100J Pd = 0.75W
COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE
QUIESCENT CURRENT = 180µA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 250mA
ALL OTHER CAPACITORS ARE CERAMIC
Figure 4A. LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology
AN54-6
3.3V
1A
AN54 • F04A
Application Note 54
Low output voltage causes efficiency degradation at light
loads when the chip’s DC supply current and gate charge
current play major parts in total losses. Figures 4B and
5B illustrate this point as the efficiency falls off below
10mA output current. High input voltage compounds the
problem.
100
100
VIN = 5V
90
VIN = 5V
90
EFFICIENCY (%)
EFFICIENCY (%)
VIN = 10V
VIN = 10V
80
70
VIN = 14V
80
VIN = 14V
70
60
60
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
50
0.001
1
0.01
0.1
OUTPUT CURRENT (A)
Figure 4B. LTC1148: (4V-14V to 3.3V/1A) Buck Converter
Measured Efficiency
C1
1µF
C2
0.1µF
3
VIN
10
6
PDRIVE
4
C4
3300pF
X7R
C5
470pF
NPO
1
Q1
Si9430DY
SHUTDOWN
ITH
LTC1148-3.3
SENSE +
SENSE –
R1
1k
C1
C3
C7
Q1
Q2
D1
R2
L1
Figure 5B. LTC1148: (4V-14V to 3.3V/2A) Buck Converter
Measured Efficiency
+
+
CT
NDRIVE
SGND
11
2
AN54 • F05B
AN54 • F04B
VIN
4V TO 14V
1
C3
22µF × 3
25V
L1
50µH
R2
0.05Ω
3.3V
2A
8
7
C6
0.01µF
+
14
PGND
Q2
Si9410DY
D1
MBRS140T3
C7
220µF × 2
10V
12
(Ta)
AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A
AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
MOTOROLA SCHOTTKY VBR = 40V
KRL SL-1-C1-0R050J Pd = 1W
COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE (THROUGH HOLE)
QUIESCENT CURRENT = 180µA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 450mA
ALL OTHER CAPACITORS ARE CERAMIC
AN54 • F05A
Figure 5A. LTC1148: (4V-14V to 3.3V/2A) Buck Converter with Surface Mount Technology
AN54-7
Application Note 54
100
LTC1148: (5V to 3.3V/5A) High Efficiency
Step-Down Converter
EFFICIENCY (%)
Many new microprocessor designs require 3.3V, yet they
are used in systems where 5V is the primary source of
power. A high efficiency 5V to 3.3V converter is drawn in
Figure 6A. It supplies up to 5A load using only surface
mount components. Two P-channel MOSFETs are connected in parallel to decrease their conduction losses.
Efficiency at 5V input is 90%; this means only 1.6W is lost.
The lost power is distributed between RSENSE, L1 and the
power MOSFETs, thus no heat sinking is required.
90
80
70
0.001
0.01
0.1
1
OUTPUT CURRENT (A)
10
AN54 • F06B
Figure 6B. LTC1148: (5V to 3.3V/5A)
Buck Converter Measured Efficiency
VIN
5V
+
C2
0.1µF
C1
1µF
3
Q2
Si9433DY
VIN
PDRIVE
1
Q1
Si9433DY
+
L1
5µH
10
6
R1
470Ω
4
C4
3300pF
C1
C3
C6
Q1, Q2
Q3
D1
R2
L1
C5
150pF
NPO
SHUTDOWN
ITH
SENSE +
8
SENSE –
7
CT
NDRIVE
SGND
11
C7
0.01µF
14
PGND
Q3
Si9410DY
D1
MBRS140T3
12
TANTALUM
PANASONIC ECG-COJB330
AVX (Ta) TPSE227K01R0080 ESR = 0.080Ω IRMS = 1.285A
SILICONIX PMOS BVDSS = 12V DCRON = 0.075Ω Qg = 60nC
SILICONIX NMOS BVDSS = 30V DCRON = 0.050Ω Qg = 30nC
MOTOROLA SCHOTTKY VBR = 30V
KRL MP-2A-C1-0R020J Pd = 3W
COILTRONICS CTX02-12483-1
Figure 6A. LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter
AN54-8
VOUT
3.3V
5A
R2
0.02Ω
LTC1148-3.3
0V = NORMAL
>2V = SHUTDOWN
C3
33µF
6.3V
×2
+
C6
220µF
10V
×3
AN54 • F06A
Application Note 54
100
LTC1148: (5V to 3.5V/3A) High Efficiency
Step-Down Converter
95
90
EFFICIENCY (%)
Some processors require 3.5V or other intermediate voltage derived from a 5V supply. A good solution for them is
the circuit in Figure 7A. An adjustable version of the
LTC1148 allows precise output voltage adjustment, while
preserving efficiencies of 95%. The output voltage is set
by resistors R3 and R4.
85
80
75
70
65
60
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
4
AN54 • F07B
Figure 7B. LTC1148: (5V to 3.5V/3A)
Measured Efficiency
VIN
5V
+
+
Q1
Si9433DY
1
C2
0.1µF
2
3
4
5
6
C5
180pF
NPO
C4
3300pF
X7R
7
R1
510Ω
NDRIVE
PDRIVE
NC
VIN
CT
INT VCC
ITH
SENSE –
NC
LTC1148
PGND
SGND
SHUTDOWN
ADJ
SENSE +
D1
MBRS130T3
14
C3
22µF
25V
×2
Q2
Si9410DY
13
L1
10µH
12
11
10 SHUTDOWN
100pF
9
R4
10k
1%
+
8
C6, 0.01µF
R2
0.033Ω
R3
18.2k
1%
C6
100µF
10V
×3
+ VOUT
C3
C6
Q1
Q2
D1
R2
L1
AVX (Ta) TPSD226M025R0200 ESR = 0.20Ω IRMS = 0.866A
AVX (Ta) TPSD107M01R0100 ESR = 0.10Ω IRMS = 1.225A
SILICONIX PMOS BVDSS = 12V DCRON = 0.110Ω Qg = 20nC
SILICONIX NMOS BVDSS = 30V DCRON = 0.05Ω Qg = 30nC
MOTOROLA SCHOTTKY VBR = 30V
KRL SL-C1-1/2-0R033J Pd = 1/2W
COILTRONICS CTX10-4 DCR = 0.038Ω Kool Mµ CORE
3.5V
3A
VOUT = 1.25V (1 + R3/R4)
AN54• F07A
Figure 7A. LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter
AN54-9
Application Note 54
Previous circuits can accept inputs up to 14V. If higher
input voltage is required the LTC1149 can be used. This IC
is designed for inputs of up to 48V. A basic step-down
application circuit is shown in Figure 8A. It operates in the
same fashion as the circuit in Figure 1A and provides
5V/2A output. However, different MOSFETs are used since
they must withstand 48V between source and drain. High
current efficiency exceeds 92% over wide range of input
voltages. Since the control and drive circuitry are powered
directly from the input line, DC bias current and gate
charge current result in slightly lower efficiency at light
and moderate loads due to high input voltage (relative to
LTC1148). This characteristic is eliminated in the circuit of
Figure 11A. A circuit board has been laid out for this circuit
and has subsequently been thoroughly tested under full
VIN
10V TO 48V
C4
1µF
C5
0.1µF
5
C6
0.068µF
Z5U
16
10
15
7
6
R1
1k
C7
3300pF
X7R
C2
C4
C10
Q1
Q2
D1
D2
R2
L1
100
90
VIN = 12V
80
VIN = 24V
VIN = 36V
60
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
C8
680pF
NPO
2
VCC
PGATE
VCC
PDRIVE
CAP
SD1
LTC1149-5
SENSE +
SD2
SENSE –
Q1
IRFU9024
C3
0.047µF
Z5U
C2
330µF
63V
L1
62µH
R2
0.05Ω
5V
2A
9
8
C9
0.01µF
+
ITH
CT
SGND
11
PGND
12
NGATE
RGND
13
Q2
IRFU024
D2
MBR160
C10
220µF × 2
10V
14
UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170Ω IRMS = 1.280A
(Ta)
SANYO (OS-CON) 10SA22OM ESR = 0.035Ω IRMS = 2.360A
IR PMOS BVDSS = 60V RDSON = 0.280Ω CRSS = 65pF Qg = 19nC
IR NMOS BVDSS = 60V RDSON = 0.100Ω CRSS = 79pF Qg = 28nC
SILICON VBR = 75V
MOTOROLA SCHOTTKY VBR = 60V
KRL NP-1A-C1-0R050J Pd = 1W
COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE
QUIESCENT CURRENT = 1.5mA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 570mA
ALL OTHER CAPACITORS ARE CERAMIC
Figure 8A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter
AN54-10
2
Figure 8B. LTC1149: (10V-48V to 5V/2A) High Voltage
Buck Converter Measured Efficiency
1
4
1
AN54 • F08B
D1
1N4148
VIN
VIN = 48V
70
+
C1
0.1µF
3
+
operating conditions and optimized for mass production
requirements. A Gerber file for the board is available upon
request.
EFFICIENCY (%)
LTC1149: (10V-48V to 5V/2A) High Voltage
Buck Converter
AN54 • F08A
Application Note 54
LTC1149: (10V-48V to 5V/2A) High Voltage Buck
Converter with Large P-Channel and N-Channel
MOSFETs
Remember, the “best” MOSFET selection depends on the
particular application.
100
VIN
10V TO 48V
C4
1µF
C5
0.1µF
5
C6
0.068µF
Z5U
16
10
15
7
6
R1
1k
C7
3300pF
X7R
C2
C4
C10
Q1
Q2
D1
D2
R2
L1
VIN = 12V
80
VIN = 24V
70
VIN = 48V
60
VIN = 36V
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
C8
680pF
NPO
VCC
PDRIVE
VCC
CAP
PGATE
SD1
LTC1149-5
SENSE +
SD2
SENSE –
1
4
2
AN54 • F09B
D1
1N4148
2
VIN
1
Figure 9B. LTC1149: (10V-48V to 5V/2A) Measured Efficiency
with Large P-Channel and N-Channel MOSFETs
+
C1
0.1µF
3
+
90
EFFICIENCY (%)
Figure 9A is similar to Figure 8A with much larger MOSFETs
(TO220 package). These transistors have lower RDS(ON)
which reduces their I2R losses by roughly a factor of 2.
However, the efficiency improves (compared to Figure
8B) only at 2A output current with minimum input voltage.
Under other conditions higher gate capacitance causes
increased gate charge current leading to higher driver
loss. Also for high input voltages (roughly greater than
24V), transition losses play a significant part. These losses
are proportional to the reverse transfer capacitance CRSS,
maximum output current, and the square of input voltage.
Larger CRSS for the oversized P-channel MOSFET causes
an efficiency drop (especially for higher input voltages).
C3
0.047µF
Z5U
Q1
IRF9Z34
C2
330µF
63V
L1
62µH
R2
0.05Ω
5V
2A
9
8
C9
0.01µF
+
ITH
CT
SGND
11
PGND
12
NGATE
RGND
13
Q2
IRFZ34
C10
220µF × 2
10V
D2
MBR160
14
UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170Ω IRMS = 1.280A
(Ta)
SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A
IR PMOS BVDSS = 60V RDSON = 0.140Ω CRSS = 100pF Qg = 34nC
IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC
SILICON VBR = 75V
MOTOROLA SCHOTTKY VBR = 60V
KRL NP-1A-C1-0R050J Pd = 1W
QUIESCENT CURRENT = 1.5mA
COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 560mA
ALL OTHER CAPACITORS ARE CERAMIC
AN54 • F09A
Figure 9A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs
AN54-11
Application Note 54
100
LTC1149: (10V-48V to 3.3V/2A) High Voltage
Buck Converter
90
VIN = 12V
EFFICIENCY (%)
If 3.3V has to be generated efficiently from a high voltage
input, use the circuit of Figure 10A. It copies the configuration presented in Figure 8A but uses the LTC1149-3.3
regulator to provide a precise 3.3V output. In spite of
the high input and low output voltages, efficiency still
reaches 92%.
80
VIN = 24V
70
60
VIN = 48V
VIN = 36V
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
2
AN54 • F10B
Figure 10B. LTC1149: (10V-48V to 3.3V/2A) High Voltage
Buck Converter Measured Efficiency
VIN
10V TO 48V
+
C1
0.1µF
3
+
C4
1µF
C5
0.1µF
C6
0.068µF
Z5U
5
16
10
15
7
6
R1
1k
C7
3300pF
X7R
C2
C4
C10
Q1
Q2
D1
D2
R2
L1
C8
470pF
NPO
D1
1N4148
2
VIN
VCC
PGATE
1
PDRIVE
4
SD1
LTC1149-3.3
SENSE +
9
SD2
SENSE –
VCC
CAP
8
Q1
IRFU9024
C3
0.047µF
Z5U
C2
330µF
63V
L1
50µH
3.3V
2A
C9
0.01µF
+
ITH
CT
SGND
11
NGATE
PGND
12
13
RGND
Q2
IRFU024
D2
MBR160
C10
220µF
10V
14
UNITED CHEMI-CON (Al) LXF63VB331M12.5 × 30 ESR = 0.170Ω IRMS = 1.280A
(Ta)
SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A
IR PMOS BVDSS = 60V RDSON = 0.280Ω CRSS = 65pF Qg = 19nC
IR NMOS BVDSS = 60V RDSON = 0.100Ω CRSS = 79pF Qg = 28nC
SILICON VBR = 75V
MOTOROLA SCHOTTKY VBR = 60V
KRL NP-1A-C1-0R050J Pd = 1W
COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE
QUIESCENT CURRENT = 1.5mA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 570mA
ALL OTHER CAPACITORS ARE CERAMIC
Figure 10A. LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter
AN54-12
R2
0.05Ω
AN54 • F10A
Application Note 54
observed that Q4 turns on when the output is less than 10V
(the internal regulator output) and stays on or off under all
conditions.
LTC1149: (10V-48V to 12V/2A) High Voltage
Buck Converter
The LTC1149 contains an internal 10V low dropout linear
regulator to provide power to the control circuitry. It
actually means that the DC bias current as well as the gate
charge current come directly from the input line, causing
slight efficiency degradation, especially for high input
voltages (additional power is dissipated by the internal
regulator). A solution for this problem is presented in
Figure 11A. When the output level reaches about 5V, Zener
D3 starts conducting and saturates Q3, which in turn
switches Q4 on. Now VCC pins 3 and 5 are powered directly
from the output. Losses caused by DC current and gate
charge current are significantly reduced allowing improved efficiency at high input voltage.
100
EFFICIENCY (%)
90
C1
0.1µF
Q4
2N3906
3
+
33k
C4
1µF
C5
0.1µF
5
16
10k
C6
0.068µF
Z5U
33k
D3
5.1V
7
Q3
2N3904
R1
1k
10k
C2
C4
C10
Q1
Q2
D1
D2
R2
L1
15
C7
3300pF
X7R
6
C8
200pF
NPO
VCC
VCC
PDRIVE
D4
1N4148
CAP
VFB
SENSE +
SENSE –
SD2
ITH
VIN = 48V
75
VIN = 36V
60
0.001
1
0.01
0.1
OUTPUT CURRENT (A)
Figure 11B. LTC1149: (10V-48V to 5V/2A) Measured
Efficiency with Large P-Channel and N-Channel
MOSFETs
1
4
10
+
Q1
IRF9Z34
C3
0.047µF
Z5U
11
PGND
12
NGATE
RGND
C2
330µF
63V
L1
62µH
9
8
VOUT
12V
2A
+
13
Q2
IRFZ34
D2
MBR160
14
UNITED CHEMI-CON (Al) LXF63VB331M12.5 × 30 ESR = 0.170Ω IRMS = 1.280A
(Ta)
SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A
IR PMOS BVDSS = 60V RDSON = 0.140Ω CRSS = 100pF Qg = 34nC
IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC
SILICON VBR = 75V
MOTOROLA SCHOTTKY VBR = 60V
KRL NP-1A-C1-0R050J Pd = 1W
COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE
R2
0.05Ω
432k
1%
C9
0.01µF
LTC1149
CT
SGND
10
AN54 • F11B
D1
1N4148
PGATE
80
65
2
VIN
85
70
The regulator output must be set up for an output voltage
less than 14.5V to provide a margin for the LTC1149 pin
5 absolute maximum rating of 16V. It should also be
VIN
10V TO 48V
VIN = 15V
95
C10
220µF × 2
10V
49.9k
1%
QUIESCENT CURRENT = 1.5mA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 560mA
ALL OTHER CAPACITORS ARE CERAMIC
AN54 • F11A
Figure 11A. LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter
AN54-13
Application Note 54
100
LTC1149: High Power Buck Converters
95
Figures 12A and 13A are examples of high power (more
than 100W) converters that use the LT1149. The regulators are powered from the full wave rectified output of a
16VRMS to 32VRMS transformer. Input capacitance is very
bulky, but it has to ensure that ripple valleys do not dip
below the minimum regulator input requirement. The
circuit in Figure 13A has additional gate driver circuits
which are required to improve MOSFET switching times.
Overall efficiency goes as high as 98%! Remember, at
these output current levels layout becomes extremely
important, and all the recommendations from the LTC1149
data sheet must be closely followed.
0.33µF
EFFICIENCY (%)
90
85
80
75
70
65
0.01
0.1
1
OUTPUT CURRENT (A)
AN54 • F12B
Figure 12B. LTC1149: (16VRMS to 13.8V/10A)
Buck Converter Measured Efficiency
0.22µF
D1
1N4148
VIN
16VRMS
RECTIFIED
Q1
RFG60P06E
0.33µF
+
1
2
3
4
5
6
7
CT
270pF
3300pF
8
CAP
VIN
SD2
VCC
RGND
PDRIVE
NGATE
VCC
D2
MBR380
10µF
PGATE
LTC1149
CT
PGND
SGND
ITH
VFB
SENSE –
SENSE +
+
CIN
20000µF
35V
SHUTDOWN
(NORMALLY GND)
14
13
12
L
33µH
11
10
100pF
R2
205k
9
470Ω
100Ω
1µF
WIMA
1.5µF
63V
WIMA
Q2
IRFZ44
16
15
10
R1
20.5k
1%
+
COUT, 1500µF
25V, × 2
VOUT
13.8V
10A
RS
0.0082Ω
1000pF
33k
100Ω
COUT PANASONIC HFQ SERIES
D2 MOTOROLA SCHOTTKY
Q1 HARRIS PMOS BV DSS = 60V RDSON = 0.03Ω
Figure 12A. LTC1149: (16VRMS to 13.8V/10A) Buck Converter
AN54-14
OUTPUT
GROUND
CONNECTION
AN54 • F12A
Application Note 54
VIN
32VRMS
RECTIFIED
MPSW06
0.33µF
D1
1N4148
0.22µF
Q1
SMP40P06
D2
MBR380
0.33µF
+
MPSA56
10µF
PDRIVE
BUFFER
1
2
3
4
5
6
7
CT
150pF
3300pF
8
PGATE
CAP
VIN
SD2
VCC
RGND
PDRIVE
NGATE
LTC1149
VCC
CT
PGND
SGND
ITH
VFB
SENSE –
SENSE +
CIN
5000µF
75V
SHUTDOWN
(NORMALLY GND)
14
1N4148
13
MPSA56 NDRIVE
BUFFER
12
L
62µH
11
10
100pF
R2
432k
9
470Ω
100Ω
1µF
WIMA
+
Q2
IRFZ34
16
15
1.5µF
63V
WIMA
+
R1
20.5k
1%
COUT, 1000µF
35V
VOUT
27.6V
5A
RS
0.016Ω
1000pF
33k
OUTPUT
GROUND
CONNECTION
100Ω
COUT PANASONIC HFQ SERIES
D2 MOTOROLA SCHOTTKY
Q1 SILICONIX PMOS BV DSS = 60V RDSON = 0.045Ω
AN54 • F13A
Figure 13A. LTC1149: (32VRMS to 27.6V/5A) Buck Converter
100
95
EFFICIENCY (%)
90
85
80
75
70
65
0.01
0.1
1
OUTPUT CURRENT (A)
10
AN54 • F13B
Figure 13B. LTC1149: (32VRMS to 27.6V/5A) Buck Converter Measured Efficiency
AN54-15
Application Note 54
100
LTC1147: (5V-14V to 5V/1A) Buck Converter with
Surface Mount Technology
VIN = 6V
90
VIN
5V TO 14V
+
EFFICIENCY (%)
The LTC1147 (Figure 14A) is a great way to implement a
high efficiency regulator using a minimum number of
external components and occupying the least board space.
This regulator provides many advantages of the LTC1148
including constant off-time configuration, low dropout
regulation and Bust Mode operation, comes in a smaller
package and does not require the N-channel MOSFET. The
only sacrifice made is synchronous rectification which
degrades the efficiency of this circuit up to three percentage points. Compare efficiency graphs in Figures 1B and
14B! Since the clamp diode D1 conducts all the time
during the off-time, a larger diode (MBRD330) is used for
this circuit. The LTC1147 is an excellent choice where the
output current is less than 1A, and where the input voltage
is less than twice the output voltage.
VIN = 10V
80
VIN = 14V
70
60
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
AN54 • F14B
Figure 14B. LTC1147: (5V-14V to 5V/1A)
Buck Converter Measured Efficiency
+
C1
0.1µF
6
C2
22µF x 2
25V
1
VIN
PDRIVE
8
Q1
Si9430DY
1
SHUTDOWN
4
3
LTC1147-5
SENSE +
SENSE –
R1
1k
2
C3
3300pF
X7R
C2
C5
Q1
D1
R2
L1
ITH
L1
100µH
2
3
R2
0.1Ω
5V
1A
5
4
C5
0.001µF
+
C6
220µF
10V
CT
C4
390pF
NPO
GND
D1
MBRD330
7
AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A
AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
MOTOROLA SCHOTTKY VBR = 30V
KRL SP-1/2-A1-0R100J Pd = 0.75W
COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE
QUIESCENT CURRENT = 190µA
TRANSITION CURRENT (Burst Mode OPERATION/
CONTINUOUS OPERATION) = 170mA
ALL OTHER CAPACITORS ARE CERAMIC
Figure 14A. LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology
AN54-16
1
AN54 • F14A
Application Note 54
100
LTC1147: (4V-14V to 3.3V/1A) Buck Converter with
Surface Mount Technology
VIN = 5V
90
EFFICIENCY (%)
Figure 15A shows another compact circuit with the
LTC1147 series. It generates 3.3V/1A output using the
same configuration as in the previous example. Despite
the lack of synchronous rectification, efficiency approaches
95% with 5V input.
VIN = 10V
80
VIN = 14V
70
60
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
AN54 • F15B
Figure 15B. LTC1147: (4V-14V to 3.3V/1A)
Buck Converter Measured Efficiency
VIN
4V TO 14V
+
+
C1
0.1µF
1
VIN
6
C2
22µF × 2
25V
PDRIVE
Q1
Si9430DY
8
1
SHUTDOWN
4
3
LTC1147-3.3
SENSE +
SENSE –
R1
1k
2
C3
3300pF
X7R
C2
C6
Q1
D1
R2
L1
ITH
C4
560pF
NPO
L1
100µH
2
3
R2
0.1Ω
5
4
C5
0.001µF
+
CT
GND
3.3V
1A
C6
220µF
10V
D1
MBRD330
7
AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A
AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A
SILICONIX BVDSS = 20V DCRON = 0.100Ω CRSS = 400pF Qg = 50nC
MOTOROLA
KRL SP-1/2-A1-0R100 Pd = 0.75W
COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE
QUIESCENT CURRENT = 170µA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 170mA
AN54 • F15A
Figure 15A. LTC1147: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology
AN54-17
Application Note 54
100
LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with
Surface Mount Technology
LTC1147-3.3
SUMIDA CDR74B
VIN = 5V
95
90
EFFICIENCY (%)
One more application circuit with LTC1147 is presented in
Figure 16A. It is optimized for 5V to 3.3V conversion with
input voltages of 4V to 8V (limited by the P-channel
MOSFET). A circuit board has been laid out for this circuit
and has subsequently been thoroughly tested under full
operating conditions and optimized for mass production
requirements. A Gerber file for the board is available upon
request.
LTC1147-3.3
SUMIDA CD54
VIN = 5V
85
80
75
70
65
60
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
2
AN54 • F16B
Figure 16B. LTC1147: (4V-8V to 3.3/1.5A)
Buck Converter Measured Efficiency
VIN
4V TO 8V
+
C2
0.1µF
Q1
P-CH
Si9433DY
1
VIN
6
0V = NORMAL
≥ 2V = SHUTDOWN
3
R1
1k
C3
3300pF
PDRIVE
LTC1147-3.3
SENSE +
SENSE –
2
8
L1
10µH
SHUTDOWN
ITH
GND
R2
0.068Ω
VOUT
3.3V
1.5A
5
C5
0.01µF
4
+
CT
C4
120pF
C1
47µF
16V
C6
100µF
10V
D1
MBRS130LT3
7
AN54 • F16A
C1 AVX TPSD476M016R0150 TANTALUM 47µF 16V
C6 AVX TPSD107M010R0100 TANTALUM 100µF 10V
D1 MOTOROLA MBRS130LT3 BVR = 30V
L1 SUMIDA CDR74B-100LC 10 µH
Q1 SILICONIX PMOS Si9433
R2 IRC LRC-LR2010-01-R068-F
ALL OTHER CAPACITORS CERAMIC
Figure 16A. LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology
AN54-18
Application Note 54
LTC1148: (10V-14V to 5V/10A) High Current
Buck Converter
only inexpensive, readily available small-signal transistors, yet allows the use of all N-channel MOSFETs. Efficiency reaches 96% (see Figure 17B).
Due to differences in physical structure between N- and Pchannel MOSFETs, the former are usually more cost
effective, more available, and provide better internal parameters for the same size. This is especially important
when high output currents are required. With 5A to 10A
output currents the use of N-channel MOSFETs in place of
P-channel is the most preferable solution. An implementation of this idea is presented in Figure 17A.
100
90
EFFICIENCY (%)
VIN = 10V
A special Q4 gate drive circuit that uses a bootstrapping
technique is added to provide required gate drive. When
pin 1 goes high it turns Q3 on, providing a path for fast Q4
gate capacitance discharge. With Q3 off, Q1 and Q2
saturate each other feeding positive voltage to Q4’s gate.
As a result Q4 turns on, and the positive pulse at its source
is AC coupled through C6 supplying bootstrapped VCC for
the gate drive “SCR.” The external driver circuit contains
VIN = 14V
70
60
50
1
OUTPUT CURRENT (A)
0.1
+
C1
1µF
R1
20k
C2
0.1µF
Figure 17B. LTC1148: (10V-14V to 5V/10A) High Current
Buck Converter Measured Efficiency
+
C6
0.47µF
R2
220
Q2
2N2222
VIN
6
R4
1k
C3
3300pF
X7R
PDRIVE
SHUTDOWN
ITH
LTC1148-5
SENSE +
SENSE –
4
C4
820pF
NPO
CT
1
Q3
VN2222LL
D2
1N4148
SGND
11
PGND
L1
33µH
R8
0.01Ω
5V
10A
C5
0.001µF
R6
100
14
NDRIVE
Q4
IRFZ44
R5
100
8
7
C7
2700µF × 2
35V
R3
220
Q1
2N3906
3
10
10
AN54 • F17B
D1
1N4148
VIN
10V TO 14V
C1
C7
C8
Q4, Q5
D1, D2
D3
80
R7
22k
+
Q5
IRFZ44
D3
1N5818
C8
2200µF × 3
16V
12
(Ta)
UNITED CHEMI-CON (Al) LXF35VB272M16 X 40 ESR = 0.018Ω IRMS = 2.900A
NICHICON (Al) UPL1C222MRH ESR = 0.028Ω IRMS = 2.010A
IR NMOS BVDSS = 60V DCRON = 0.028Ω CRSS = 310pF Qg = 69nC
MOTOROLA SILICON VBR = 75V
MOTOROLA SCHOTTKY VBR = 30V
R8
L1
KRL NP-2A-C1-0R010J Pd = 3W
COILTRONICS CTX33-10-KM DCR = 0.010Ω Kool Mµ CORE
ALL OTHER CAPACITORS ARE CERAMIC
QUIESCENT CURRENT = 22mA
AN54 • F17A
Figure 17A. LTC1148: (10V-14V to 5V/10A) High Current Buck Converter
AN54-19
Application Note 54
Two resistors are placed in series with the current sense
pins. This significantly improves circuit noise immunity
which is of great importance when switching high current.
R7, connected between pin 7 and ground, disables Burst
Mode operation so that the regulator operates continuously.
an output referenced to ground is required. PGATE pin 1
provides the same drive signal referenced to VCC.
100
90
EFFICIENCY (%)
LTC1149: (12V-36V to 5V/5A) High Current, High
Voltage Buck Converter
Figure 18A shows a high current, high voltage buck
converter. The LTC1149 is used to accommodate the input
voltage requirement. As in Figure 17A the top N-channel
MOSFET is driven by an external circuit which inverts the
chip’s P-drive output and uses bootstrapping to provide
positive gate-source voltage. The peak-to-peak gate voltage is defined by the DC portion of the gate driver VCC.
Therefore, not to exceed maximum gate voltage for the
MOSFET, D1’s anode is connected to internal 10V regulator output. In this application PDRIVE pin 4 is used because
D1
1N4148
VIN
12V TO 36V
C1
0.1µF
+
C2
1µF
C3
0.1µF
5
16
10
15
7
C4
3300pF
X7R
C2
C8
C9
Q1
Q2
Q3
Q4
R1
1k
6
C5
820pF
NPO
VIN
PGATE
VCC
CAP
PDRIVE
LTC1149-5
SD1
SENSE +
SD2
SENSE –
4
VIN = 36V
1
OUTPUT CURRENT (A)
Figure 18B. LTC1149: (12V-36V to 5V/5A) High Current, High
Voltage Buck Converter Measured Efficiency
+
R4
220Ω
C7
0.22µF
Q3
VN2222LL
Q2
2N2222
9
11
12
NGATE
RGND
13
5V
5A
Q5
IRFZ34
D3
MBR160
+
C9
220µF × 2
10V
14
(Ta)
NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A
SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A
PNP BV CEO = 30V
NPN BVCEO = 40V
SILICONIX NMOS BVDSS = 60V RDSON = 5.000Ω
MOTOROLA NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 40nC
Q5
D1, D2
D3
R7
L1
IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC
SILICON VBR = 75V
MOTOROLA SCHOTTKY VBR = 60V
KRL NP-2A-C1-0R020J Pd = 3W
COILTRONICS CTX50-5-52 DCR = 0.021Ω #52 IRON POWDER CORE
ALL OTHER CAPACITORS ARE CERAMIC
Figure 18A. LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter
AN54-20
R7
0.02Ω
C6
0.001µF
R6
100Ω
PGND
L1
50µH
R5
100Ω
ITH
CT
SGND
C8
1000µF
63V
Q4
MTP30N06EL
8
5
AN54 • F18B
D2
1N4148
1
70
0.1
R3
220Ω
VCC
VIN = 24V
50
2
3
80
60
Q1
2N3906
R2
10k
VIN = 12V
AN54 • F18A
Application Note 54
100
LTC1149: (12V-48V to 5V/10A) High Current, High
Voltage Buck Converter
VIN = 12V
90
EFFICIENCY (%)
The circuit in Figure 19A uses the same configuration but
is designed to provide up to 10A output current. Besides
the usual external component changes, the circuit uses
higher current MOSFETs to improve efficiency at maximum power levels. Efficiency at 5A output is several
percentage points better than in the previous example
(compare Figures 18B and 19B). R7 keeps the regulator in
continuous mode causing the rapid efficiency decrease at
lighter loads.
VIN = 24V
VIN = 48V
80
70
VIN = 36V
60
50
1
OUTPUT CURRENT (A)
0.1
10
AN54 • F19B
Figure 19B. LTC1149: (12V-48V to 5V/10A) High Current,
High Voltage Buck Converter Measured Efficiency
D1
1N4148
VIN
12V TO
48V
+
R2
20k
C1
0.1µF
+
C2
1µF
C3
0.1µF
5
16
10
15
7
C4
3300pF
X7R
C2
C8
C9
Q1
Q2
Q3
Q4
Q5
R1
1k
6
C5
820pF
NPO
VIN
VCC
PGATE
VCC
PDRIVE
CAP
SD1
LTC1149-5
SENSE +
SD2
SENSE –
1
4
D2
1N4148
Q2
2N2222
Q4
IRFZ34
Q3
VN2222LL
R6
100Ω
11
PGND
12
NGATE
RGND
13
R7
22k
14
(Ta)
NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A
NICHICON (Al) UPL1C222MRH ESR = 0.028Ω IRMS = 2.010A
PNP BVCEO = 30V
NPN BVCEO = 40V
SILICONIX NMOS BVDSS = 60V RDSON = 5.000Ω
IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC
IR NMOS BVDSS = 60V RDSON = 0.028Ω CRSS = 310pF Qg = 69nC
R8
0.01Ω
5V
10A
C6
0.001µF
ITH
CT
SGND
L1
33µH
R5
100Ω
9
8
C8
1000µF × 2
63V
C7
0.22µF
R3
220Ω
2
3
+
R4
220Ω
Q1
2N3906
D1, D2
D3
R8
L1
Q5
IRFZ44
+
D3
MBR160
C9
220µF × 3
16V
SILICON VBR = 75V
MOTOROLA SCHOTTKY VBR = 60V
KRL NP-2A-C1-0R010J Pd = 3W
COILTRONICS CTX33-10-KM DCR = 0.010Ω Kool Mµ CORE
ALL OTHER CAPACITORS ARE CERAMIC
QUIESCENT CURRENT = 26mA
AN54 • F19A
Figure 19A. LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter
AN54-21
Application Note 54
100
LTC1149: (32V-48V to 24V/10A) High Current, High
Voltage Buck Converter
EFFICIENCY (%)
If an output voltage other than 5V or 3.3V is required, an
adjustable version of the regulator must be used. A 24V/
10A example is shown in Figure 20A. The output voltage
is set by resistors R8 and R9. The LTC1149 monitors VFB
(pin 10) keeping it at 1.25V. Similar to the previous two
circuits, an external gate driver is added to switch the
N-channel MOSFET Q2. To ensure consistent start-up of
the bootstrapping circuitry, the driver is initially powered
by R2 and D2. (The main requirement at start-up is to
supply the driver with VCC that exceeds output target
voltage.) After the switching starts, D1 an D3 power the
external gate drive circuit.
10
Figure 20B. LTC1149: (32V-48V to 24V/10A) High Current,
High Voltage Buck Converter Measured Efficiency
C2
1µF
C3
0.1µF
5
16
VCC
VCC
PDRIVE
CAP
LTC1149
VFB
15
7
C4
3300pF
X7R
C2
C9
C10
Q4, Q5
Q1
Q2
D1, D2, D3, D4
D5
R10
L1
R1
1k
6
C5
270pF
NPO
R11
39k
SD2
SENSE +
SENSE –
ITH
CT
SGND
11
PGND
12
C7
0.22µF
NGATE
RGND
Q2
MPS651
1
4
Q3
VN2222LL
Q4
IRFZ44
D4
1N4148
R6
100Ω
9
C7
0.001µF
8
C6
100pF
Q5
IRFZ44
24V
10A
+
C10
1000µF × 3
35V
R10
0.01Ω
VOUT = 1.25V (1 + R8/R9)
QUIESCENT CURRENT = 26mA
TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 1.5A
ALL OTHER CAPACITORS ARE CERAMIC
Figure 20A. LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter
AN54-22
R8
220k
1%
R9
12k
1%
R7
100Ω
13
(Ta)
NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A
NICHICON (Al) UPL1V102MRH ESR = 0.029Ω IRMS = 1.980A
IR NMOS BVDSS = 60V RDSON = 0.028Ω CRSS = 310pF Qg = 69nC
PNP BVCEO = 50V
NPN BVCEO = 60V
SILICON VBR = 75V
MOTOROLA SCHOTTKY VBR = 60V
KRL NP-2A-C1-0R010J Pd = 3W
COILTRONICS CTX50-10-KM DCR = 0.010Ω Kool Mµ CORE
L1
50µH
D5
MBR160
10
14
C8
1000µF × 2
63V
R5
220Ω
R4
220Ω
PGATE
+
D3
1N4148
R3
20k
2
+
10A
AN54 • F20B
Q1
2N5087
VIN
100
1A
OUTPUT CURRENT (mA)
R2
5.1k
VIN
32V TO 48V
3
70
50
D2
1N4148
C1
0.1µF
VIN = 45V
80
60
D1
IN4148
+
VIN = 32V
90
AN54 • F20A
Application Note 54
Figure 21A provides the function of a step-up and stepdown converter without using a transformer. This topology is called a SEPIC converter. The P-channel transistor
and L1 are arranged similarly to a buck-boost topology
providing the boost part of the regulator. Pulses at Q2’s
drain (actually two paralleled devices) are coupled via C8
to the buck portion that includes Q3 and L2. This circuit
accepts 4V to 14V input and provides a solid 5V output.
Even though the schematic shows two inductors, they
carry the same current and can be wound on a single core.
Such dual coils are readily available (see circuit parts list).
This topology is acceptable for moderate loads only, as the
coupling capacitor C8 carries the full load current and
must be sized accordingly. When the sense resistor is
placed at ground potential, such as the case in this circuit,
the off-time increases approximately 40%.
current sense resistor is placed at ground. This allows to
provide different output voltages. D2 is included for foldback
short-circuit protection. When VOUT equals zero (output is
shorted) D2 clamps pin 6 and limits the output current.
100
VIN = 5V
+
VIN = 5V
PDRIVE
INT VCC
VFB
0.01
0.1
OUTPUT CURRENT (A)
1
AN54 • F21B
Figure 21B. LTC1148: (4V-14V to 5V/1A)
Buck-Boost Converter Measured Efficiency
+
C8
220µF
10V
3
VIN
5
70
+
C2
0.1µF
VIN = 4V
VIN = 14V
50
0.001
Q2
Si9430DY x 2
C1
1µF
VIN = 4V
80
60
An adjustable version of the regulator is required when the
VIN
4V TO
14V
VIN = 10V
90
EFFICIENCY (%)
LT1148: (4V-14V to 5V/1A) SEPIC Converter
1
C7
100µF
20V L2
50µH
VOUT
5V
1A
R3
75k
1%
L1
50µH
9
LTC1148
10
D2
MBR0520L
6
TO VOUT
R1
1k
C4
3300pF
X7R
C1
C7
C8, C10
Q2
Q3
D1
R2
L1
4
C5
390pF
NPO
SHUTDOWN
ITH
SENSE +
SENSE –
CT
SGND
11
NDRIVE
PGND
8
7
+
C6
0.1µF
R2
0.082Ω
D1
1N5818
14
12
(Ta)
SANYO (OS-CON) 20SA100M ESR = 0.037Ω IRMS = 2.250A
SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
MOTOROLA SCHOTTKY VBR = 30V
KRL NP-1A-C1-0R082J Pd = 1W
COILTRONICS CTX50-4P, CTX50-5P
R4
25k
1%
C10
220µF
10V
Q3
Si9410DY
C9
100pF
VOUT = 1.25V (1 + R3/R4)
QUIESCENT CURRENT = 200µA
TRANSITION CURRENT (Burst Mode OPERATION/
CONTINUOUS OPERATION) = 250mA/VIN = 5V
ALL OTHER CAPACITORS ARE CERAMIC
AN54 • F21A
Figure 21A. LTC1148: (4V-14V to 5V/1A) SEPIC Converter
AN54-23
Application Note 54
100
LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A)
Split Supply Converter
VIN = 5V
VIN = 10V
90
EFFICIENCY (%)
Applications requiring a split supply can use the circuit
presented in Figure 22A. It contains the converter from
Figure 21A and adds a synchronous charge pump Q4 to
provide a –5V output. Q4 source is referenced to the –5V
line, and its gate drive is AC coupled via C11 and clamped
by D3. The outputs exhibit excellent tracking with line and
load changes. This is a great way to build a dual output
converter without any transformer.
80
VIN = 4V
VIN = 14V
70
60
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
0.5
AN54 • F22B
Figure 22B. LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A)
Split Supply Converter Measured Efficiency
VIN
4V TO
14V
Q2
Si9430DY
+
C2
0.1µF
3
VIN
PDRIVE
5
INT VCC
SENSE +
1
D4
MBR0520L
6
VOUT
R1
1k
C5
390pF
NPO
C4
3300pF
X7R
C1
C8
C9, C10, C12
Q2
Q3, Q4
D1, D2
R2
L1
4
SHUTDOWN
7
VFB
SGND
11
L2
50µH
L1
50µH
R3
75k
1%
C7
0.1µF
R2
0.05Ω
NDRIVE
PGND
12
+
C10
220µF
10V
+
C12
220µF
10V
9
Q3
Si9410DY
14
D1
1N5818
C6
100pF
C11
0.22µF
(Ta)
SANYO (OS-CON) 20SA100M ESR = 0.037Ω IRMS = 2.250A
SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A
Q4
Si9410DY
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
MOTOROLA SCHOTTKY VBR = 30V
KRL NP-1A-C1-0R082J Pd = 1W
COILTRONICS CTX50-4
VOUT = 1.25V (1 + R3/R4)
D2
1N5818
QUIESCENT CURRENT = 250µA
TRANSITION CURRENT (DIS/CONT) = 130mA/VIN = 5V
R5
51k
Figure 22A. LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter
AN54-24
+VOUT
5V
0.5A
SENSE –
ITH
CT
C8
100µF
20V
8
LTC1148
10
+
+
C1
1µF
C9
220µF
10V
D3
1N4148
R4
25k
1%
–VOUT
–5V
0.5A
AN54 • F22A
Application Note 54
100
LTC1148: (4V-10V to –5V/1A) Positive-to-Negative
Converter
95
VIN
4V TO
10V
EFFICIENCY (%)
85
80
10V TO –5V/1A
75
70
65
60
0.001
+
C1
1µF
C2
0.1µF
Q1
TP0610L
Figure 23B. LTC1148: (4V-10V to – 5V/1A)
Positive-to-Negative Converter Measured
Efficiency
6
4
R1
1M
R2
1k
C3
6800pF
X7R
+
C7
150µF × 2
16V
INT VCC
SENSE +
SHUTDOWN
SENSE –
ITH
VFB
CT
C4
560pF
NPO
NDRIVE
SGND
11
L1
50µH
1
8
LTC1148
10
10
3
PDRIVE
5
1
0.01
0.1
OUTPUT CURRENT (A)
AN54 • F23B
Q2
Si9430DY
VIN
SHUTDOWN
4V TO –5V/1A
90
Figure 23A shows a buck-boost converter using the
LTC1148. This is an inverting topology, and it can inherently buck or boost the input voltage. Ground pins of the
chip are referenced to the output line; no additional level
shifting circuit is required to drive the N-channel FET Q3
(its source is referenced to – 5V as well). Now even with
minimum input level, the circuit provides a solid 9V peakto-peak MOSFET drive signal. However, so as not to
exceed absolute maximum voltage at pin 3, the input line
is limited to 10V. If the circuit is required to accept a higher
input voltage, the LTC1148HV can be used instead. Q1 is
added to provide a logic level shutdown feature. If shutdown is not needed omit Q1 and R1, and short pin 10 to
pin 11.
7
C5
0.01µF
R2
0.05Ω
R3
75k
1%
9
14
PGND
12
C6
200pF
Q3
Si9410DY
+
D1
1N5818
R4
25k
1%
C8
220µF × 2
10V
– 5V
1A
C1
C7
C8
Q2
Q3
D1
R2
L1
(Ta)
SANYO (OS-CON) 16SA150M ESR = 0.035Ω IRMS = 2.280A
SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
MOTOROLA SCHOTTKY VBR = 30V
KRL NP-1A-C1-0R050J
COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE
ALL OTHER CAPACITORS ARE CERAMIC
VOUT = 1.25V (1 + R3/R4)
AN54 • F23A
Figure 23A. LTC1148: (4V-10V to – 5V/1A) Positive-to-Negative Converter
AN54-25
Application Note 54
95
LTC1148: (5V-12V to – 15V/0.5A) Buck-Boost
Converter
90
EFFICIENCY (%)
Figure 24A presents an inverting regulator designed to
accommodate higher output voltages. The LTC1148 cannot accept feedback directly from a negative output. To
regulate negative outputs, the feedback must be inverted
and compared against 1.25V. This function is provided by
a DC level shifting amplifier consisting of Q1 and associated components. Resistor R4 provides amplifier negative
feedback, effectively cancelling variations in VCC, and Q2
provides temperature compensation. The output voltage
is set by resistors R4 and R5. As usual, with the sense
resistor at ground potential, the off-time increases roughly
by 40%.
85
80
12V TO –15V/0.5A
75
5V TO –15V/0.5A
70
65
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
AN54 • F24B
Figure 24B. LTC1148: (5V-12V to –15V/0.5A)
Buck-Boost Converter Measured Efficiency
VIN
5V TO 12V
+
C2
0.1µF
U1
3
10
> 1.5V = SHUTDOWN
6
R6
1k
C5
6800pF
4
C6
200pF
11
+
Q3
Si9435DY
×2
C3
1µF
C7
220µF
10V
R3
56k
1
PDRIVE
VIN
SHUTDOWN
LTC1148
ITH
CT
SGND
SENSE +
SENSE –
VFB
PGND
L1
50µH
8
7
Q2
2N5210
C8
0.01µF
R7
0.033Ω
Q1
2N5210
9
12
R7
DALE LVR-3 0.033W
L1 COILTRONICS CTX50-5-52
C7
SANYO OS-CON 105A220K
C9, C10 SANYO OS-CON 255C47K
C11
200pF
D3
MBR735
+
R4
49.9k
1%
C9
47µF
25V
+
C10
47µF
25V
R5
634k
1%
VOUT
–15V
0.5A
AN54 • F24A
Figure 24A. LTC1148: (5V-12V to –15V/0.5A) Buck-Boost Converter
AN54-26
Application Note 54
LTC1148: (2V-5V to 5V/1A) Boost Converter
100
95
Even though the LTC1148 is mainly used in step-down
converters, it can also show excellent performance in the
boost configuration. A boost implementation is shown in
Figure 25A. This is a two-cell to 5V converter that uses the
LT1109 to provide 12V to power the main regulator chip
(unfortunately, MOSFETs do not operate with only 2V at the
gate). The LT1109 is a small micropower IC that requires
only three external components and provides great efficiency. An N-channel transistor is used as the switch, and
general purpose MOSFETs Q1 and Q2 are used to form an
inverting gate driver. When Q3 turns off, the voltage at its
drain rises above VIN, and a Schottky diode D2 starts
conducting. In a short period of time Q4 shorts it out
providing a synchronous rectification feature and increasing efficiency. If 12V is already available, the LT1109 can be
omitted and the 12V line connected directly to pin 3.
4V TO 5V/1A
EFFICIENCY (%)
90
VIN
2V TO
5V
1
+
VR1
VIN
SW
7
SHUTDOWN
S/D
LT1109
SENSE
D1
1N5818
70
65
0.001
1
AN54 • F25B
Figure 25B. LTC1148: (2V-5V to 5V/1A)
Boost Converter Measured Efficiency
D2
1N5818
L2
25µH
5V
1A
C1
100µF
10V
Q4
Si9410
12V
8
C2
0.1µF
4
+
C3
1µF
3
PDRIVE
SENSE +
10
6
4
C5
390pF
NPO
SHUTDOWN
SENSE –
LTC1148
VFB
ITH
CT
NDRIVE
PGND
SGND
11
R3
75k
1%
Q1
TP0610L
VIN
C4
6800pF
X7R
0.01
0.1
OUTPUT CURRENT (A)
3
GND
R2
1k
2V TO 5V/1A
80
75
R1
0.05Ω
L1
33µH
85
1
8
7
+
Q3
Si9410
C8
220µF × 2
10V
Q2
VN2222LL
C6
0.001µF
9
14
12
C1
SANYO (OS-CON) 10SA100M ESR = 0.045Ω IRMS = 1.870A
C3
(Ta)
C8
SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A
Q3, Q4 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
D1, D2 MOTOROLA SCHOTTKY VBR = 30V
C7
100pF
R2
L1
L2
R4
25k
1%
KRL SL-1-C1-0R050J Pd = 1W
COILTRONICS CTX33-1 DCR = 0.220Ω Kool Mµ CORE
COILTRONICS CTX25-4
VOUT = 1.25V (1 + R3/R4)
AN54 • F25A
Figure 25A. LTC1148: (2V-5V to 5V/1A) Boost Converter
AN54-27
Application Note 54
LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A)
Dual Buck Converter
95
A circuit that provides dual 3.3V/5V output is shown in
Figure 26A. It uses a dual LTC1143 regulator that combines two LTC1147, non-synchronous switching regulators. The efficiency was measured with only one output
loaded which provided worse results for low output current due to the presence of the second half’s quiescent
current. This circuit provides very simple means to power
dual voltage logic. It occupies small amount of board
space and is very efficient!
85
EFFICIENCY (%)
90
8V TO 5V
8V TO 3.3V
80
14V TO 5V
14V TO 3.3V
75
70
65
60
0.001
0.01
0.1
1
OUTPUT CURRENT (A)
10
AN54 • F26B
Figure 26B. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A)
Dual Buck Converter Measured Efficiency
VIN
5.2V TO 14V
CIN3
22µF
25V
×2
VOUT3
3.3V/2A
RSENSE3
0.05Ω
+
L1
20µH
+
0.22µF
Q1
P-CH
Si9430DY
13
4
1
VIN3
0V = NORMAL
>1.5V = SHUTDOWN
10
2
SHUTDOWN 3
16
COUT3
220µF
10V
×2
D1
MBRD330
VIN5
PDRIVE5
PDRIVE3
SENSE + 3
SENSE + 5
12
3
ITH5
CT5
GND5
15
7
6
11
RC3
1k
RC5
1k
ITH3
14
CT3
390pF
CC3
3300pF
L2
20µH
VOUT5
5V/2A
CC5
3300pF
8
CT5
200pF
Figure 26A. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter
AN54-28
RSENSE5
0.05Ω
0.01µF
SENSE – 5
CT3
CIN5
22µF
25V
×2
9
LTC1143
SENSE – 3
GND3
KRL SL-1R050J
RSENSE:
L1, L2:
COILTRONICS CTX20-4
AVX (Ta) TPSD226K025R0200
CIN3, CIN5:
COUT3, COUT5: AVX (Ta) TPSE227K010R0080
Q1, Q2:
SILICONIX PMOS Si9430DY
Q2
P-CH
Si9430DY
5
SHUTDOWN 5
0.01µF
+
0.22µF
D2
MBRD330
+
COUT5
220µF
10V
×2
AN54 • F26A
Application Note 54
100
LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage
Buck Converter
7V TO 5V
95
90
12V TO 5V
EFFICIENCY (%)
The standard LTC1148 input voltage is limited to 16V
absolute maximum level, which is not sufficient in some
applications. Figure 27A shows a step-down regulator
using the high voltage LTC1148HV. It contains the same
internal functions but accepts up to 20V input (remember,
MOSFET’s gates are usually rated at 20V maximum). As a
building block it can be used in the same manner as
LTC1148. Input tantalum capacitors now have to be rated
at 35V to ensure reliable operation under maximum input
voltage.
85
80
75
18V TO 5V
70
65
60
55
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
AN54 • F27B
Figure 27B. LTC1148HV-5: (5.2V-18V to 5V/1A) High
Voltage Buck Converter Measured Efficiency
VIN
5.2V TO 18V
Q1
Si9430DY
+
D1
MBRS140T3
CIN
10µF
35V
×2
Q2, Si9410DY
1
1µF
+
2
3
4
CT
220pF
5
6
CC
3300pF
7
PDRIVE
NDRIVE
NC
NC
LTC1148HV-5
VIN
PGND
CT
SGND
INT VCC SHUTDOWN
ITH
SENSE –
NC
SENSE +
14
13
L1
50µH
12
11
10
SHUTDOWN
9
+
8
RC
1k
1000pF
COUT
220µF
10V
AVX
R1
0.1Ω
VOUT
5V/1A
CIN
COUT
L1
R1
Q1
Q2
AVX (Ta) TPSD106K035R0300
AVX (Ta) TPSE227K010R0080
COILTRONICS CTX50-4
KRL SP-1/2-A1-0R100
SILICONIX PMOS Si9430DY
SILICONIX NMOS Si9410DY
AN54 • F27A
Figure 27A. LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter
AN54-29
Application Note 54
100
LTC1148HV-3.3 (4V-18V to 3.3V/1A) High Voltage
Buck Converter
4V to 3.3V
95
90
EFFICIENCY (%)
Figure 28A: Here is a high voltage version of the circuit
shown in Figure 4A with input voltage increased to 18V.
85
12V to 3.3V
80
75
18V to 3.3V
70
65
60
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
AN54 • F28B
Figure 28B. LTC1148HV-3.3: (4V-18V TO 3.3V/1A)
High Voltage Buck Converter Measured Efficiency
VIN
4V TO 18V
Q1
Si9430DY
+
D1
MBRS140T3
CIN
22µF
35V
×2
Q2, Si9410DY
1
1µF
+
2
3
4
CT
270pF
5
6
CC
3300pF
7
RC
1k
PDRIVE
NDRIVE
NC
NC
LTC1148HV-3.3
VIN
PGND
CT
SGND
INT VCC SHUTDOWN
ITH
SENSE –
NC
SENSE +
14
13
L1
50µH
12
11
10
SHUTDOWN
9
+
8
1000pF
COUT
220µF
10V
0.1Ω
VOUT
3.3V/1A
CIN
COUT
L1
R1
Q1
Q2
AVX (Ta) TPSE226K035R0300
AVX (Ta) TPSE227K010R0080
COILTRONICS CTX50-4 Kool Mµ CORE
IRC LR2010-01-R100-G
SILICONIX PMOS Si9430DY
SILICONIX NMOS Si9410DY
Figure 28A. LTC1148HV-3.3: (4V-18V to 3.3V/1A)
High Voltage Buck Converter
AN54-30
AN54 • F28A
Application Note 54
100
LTC1148HV: (12.5V-18V to 12V/2A) High Voltage
Buck Converter
95
90
EFFICIENCY (%)
Figure 29A is another application of the LTC1148HV which
is configured as a step-down converter to provide 12V/2A
output. With this low dropout regulator, the input can go
as low as 12.5V and still produce a regulated output.
Resistors R2 and R3 set the output voltage level.
85
80
75
70
65
60
0.001
1
0.01
0.1
OUTPUT CURRENT (A)
10
AN54 • F29B
Figure 29B. LTC1148HV: (16V to 12V/2A) High Voltage
Buck Converter Measured Efficiency
VIN
12.5V
TO 18V
+
+
C1
1µF
C2
0.1µF
3
VIN
10
PDRIVE
R1
1k
C4
3300pF
X7R
C1
C7
Q1
Q2
D1
R2
L1
4
C5
150pF
NPO
Q1
Si9430DY
SHUTDOWN
SENSE –
ITH
VFB
CT
NDRIVE
SGND
11
R2
0.05Ω
47µH
LTC1148HV
SENSE +
6
1
C3
22µF x 2
35V
12V
2A
8
7
C6
0.01µF
432k
1%
9
14
Q2
Si9410DY
PGND
12
D1
MBRS140T3
49.9k
1%
+
C7
150µF × 3
16V
100pF
(Ta)
SANYO (OS-CON) 16SA150M
SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC
SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC
MOTOROLA SCHOTTKY VBR = 40V
KRL SL-1-C1-0R050J Pd = 1W
COILTRONICS CTX47-5P
AN54 • F29A
Figure 29A. LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter
AN54-31
AN54-32
C2, C3, C6, C7, C9
C11, C12
C20, C21
L1
0V = 12V OFF
>3V = 12V ON
(6V MAX)
DO NOT FLOAT
12V ENABLE
–VIN
C16
390pF
50V
SHUTDOWN
(TTL INPUT)
SHUTDOWN
(TTL INPUT)
+VIN
6.5V TO 14V
C17
200pF
50V
R8
510Ω
C4
3300pF
C15
1µF
50V
24
17
3
2
1
Q1
VN7002
R5
18k
C19
1000pF
7
6
4
5
NC7
NC6
NC4
8
VIN
GND
3
ADJ
VOUT
LT1121CS8
SHDN
R1
100Ω
4
Q2
Si9430DY
R2
100Ω
Q3
Si9410DY
C18
2200pF
2
1
+
7
4
C10
20pF
C20
220µF
10V
R10
0.040Ω
8
3
9
2
D2
MBRS140
+
10
T1
1
R4
294k
1%
+
5
C9
22µF
25V
+
+
–
12V/150mA
C8
22µF
35V
+
2
1
+
C11
100µF
10V
+
C12
100µF
10V
C3
22µF
25V
–
5V/2A
+
L1
33µH
2A
CTX33-4
R9
0.050Ω
3
4
D1
MBRS140
C2
22µF
25V
SHUTDOWN PINS 2 AND 16 MUST ACTIVELY BE DRIVEN
EITHER HIGH OR LOW AND NOT ALLOWED TO FLOAT.
+
C21
220µF
10V
C5
0.1µF
6
30µH, 2A
LPE-6562-A026
1.8T
R6
22
C7
22µF
25V
D3
MBRS140
C13
1000pF
C6
22µF
25V
R3
649k
1%
+
Q5
Si9410DY
Q4
Si9430DY
Figure 30A. LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A) Triple Output Buck Converter
R9 IRC LR2512-R050
R10 IRC LR2512-R040
T1
DALE, LPE-6562-AO26
3
VIN3
23
PDRIVE3
7
NC
6
NDRIVE3
1
SENSE+3
28
SENSE –3
9
PDRIVE5
21
LTC1142
NC
20
NDRIVE5
16
15
+
SHUTDOWN5
SENSE 5
11
CT5
13
14
ITH5
SENSE – 5
12
INTV CC5
5
8
NC
NC
4
18
PGND3
PGND5
22
19
NC
NC
SGND3
SGND5
AVX (Ta) TPSD226M025R0200
AVX (Ta) TPSD107K010R0100
AVX (Ta) TPSE227M010R0100
COILTRONICS CTX33-4
R7
510Ω
C1
3300pF
10
VIN5
2
SHUTDOWN3
25
CT3
27
ITH3
26
INT VCC3
C14
1µF
50V
–
3.3V/2A
+
AN54 • F30A
+
Application Note 54
Application Note 54
100
LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A)
Triple Output Buck Converter
LTC1142-5
VIN = 8V
90
EFFICIENCY (%)
LTC1142 is a dual output synchronous switching regulator controller. Two independent controller blocks
(LTC1148-based) simultaneously provide 3.3V and 5V
outputs. The circuit in Figure 30A shows an application of
this IC; it generates triple output voltages with 12V for
flash memory programming in addition to the usual logic
power levels. The 3.3V section is a regular buck converter
circuit, the 5V section contains an off-the-shelf transformer T1 in place of the inductor. The secondary winding
is used to boost the output level which is rectified and
regulated by an LT1121 to provide a clean and stable 12V
output. A turns ratio of 1:1.8 is used to ensure that the
input voltage to the LT1121 is high enough to keep the
regulator out of dropout. With LTC1142 synchronous
switching, the auxiliary 12V output may be loaded without
regard to the 5V primary output load as long as the loop
remains in continuous operation mode. Continuous operation is ensured by R5 which inhibits Burst Mode
whenever the 12V output is enabled (enable line goes
high). Make sure that the enable lines are not floating and
are driven by TTL level signals. A circuit board has been
laid out for this circuit and has subsequently been thoroughly tested under full operating conditions and optimized for mass production requirements. A Gerber file for
the board is available upon request.
95
85
LTC1142-3.3
VIN = 8V
80
75
70
65
60
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
2.5
AN54 • F30B
Figure 30B. LTC1142:(6.5V-14V to 3.3V/2A, 5V/2A,
12V/0.15A) Triple Output Buck Converter
Measured Efficiency
AN54-33
Application Note 54
LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A)
High Voltage Triple Output Buck Converter
100
Figure 31A shows the same configuration as Figure 30A
using the high voltage LTC1142HV. Circuit operation is
identical, but now it can accept up to 18V at the input.
90
LTC1142-5
VIN = 8V
EFFICIENCY (%)
95
LTC1142-3.3
VIN = 8V
85
80
75
70
65
60
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
2.5
AN54 • F30B
Figure 31B. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A,
12V/0.15A) Measured Efficiency
VIN
6.5V TO
18V
C1
22µF
25V
×2
+
+
VOUT3
3.3V/2A
23
L1
33µH
RSENSE3
0.05Ω
1
C3
100µF
10V
×2
10
VIN5
SHUTDOWN 5
PDRIVE5
PDRIVE3
SENSE + 3
SENSE + 5
Q2
Si9430DY
6
Q5
Si9410DY
SENSE –
4
1.8T
30µH
RSENSE5
0.04Ω
R2
100Ω
1000pF
3
SENSE 5
R1
100Ω
NDRIVE5
SGND3 CT3
3
25
ITH3
ITH5
27
CT5
13
510Ω
SGND5
PGND5
17
18
11
VOUT5
5V/2A
15
–
NDRIVE3
PGND3
T1
9
LTC1142HV
28
+
16
SHUTDOWN 3
2000pF
D1
MBRS140
1µF
2
24
VIN3
Q4
Si9430DY
C2
22µF
25V
×2
+
+
0V = NORMAL
>1.5V = SHUTDOWN
1µF
14
D2
MBRS140
20
Q3
Si9410DY
Q1
VN7002
510Ω
R5
18k
C4
220µF
10V
×2
+
CT3
3300pF 3300pF CT5
390pF
200pF
12V ENABLE
0V = 12V OFF
>3V = 12V ON
(6V MAX)
+
12V/150mA
C1, C2
C3, C4
L1
RSENSE3
RSENSE5
T1
AVX (Ta) TPS226K035R0300
AVX (Ta) TPSD227K010R0100
COILTRONICS CTX33-4
KRL SL-C1-1/2-0R050J
KRL SL-C1-1/2-0R040J
DALE LPE-6562-A026
PRIMARY: SECONDARY = 1:1.8
22µF
25V
+
20pF
R3
660k
VOUT
SHUTDOWN
ADJ
R4
300k
D3
MBRS140
1000pF
LT1121
VIN
GND
Figure 31A. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter
AN54-34
22µF
35V
22Ω
AN54•F31A
Application Note 54
LTC1148: High Efficiency Charger Circuit
The LTC1148 regulator can be used as a highly efficient
battery charging device. Figure 32 shows a circuit that is
programmable for 1.3A fast charge or 100mA trickle
charge mode. During the fast charge interval, the resistor
divider network (R4 and R5) forces the LTC1148 feedback
pin below 1.25V causing the regulator to operate at the
maximum output current. Sense resistor R3 controls the
current at approximately 1.3A. When the batteries are
disconnected, the error amplifier sets the output voltage to
be 8.1V (for proper operation this voltage should exceed
VIN
8V TO
15V
+
C1
1µF
0V = NORMAL
> 1.5A = SHUTDOWN
C2
0.1µF
10
6
Q3
VN2222LL
R2
1k
C4
3300pF
X7R
4
C5
200pF
NPO
C3
22µF × 2
35V
3
PDRIVE
1
SENSE –
VFB
CT
NDRIVE
SGND
11
L1
50µH
4
LTC1148
ITH
1
Q1
Si9430DY
SHUTDOWN
SENSE +
“1”
TRICKLE
CHARGE
Dual rate charging is controlled by Q3 which selects
between fast and trickle charge. When the transistor turns
on, R1 limits error amplifier output so that the current
limiter starts operating at 100mA. If the trickle charge
current needs to be altered, adjust R1. With 1.3A output
current, this charger is capable of efficiency in excess of
90% which minimizes power dissipated in surface mount
components.
+
VIN
R1
51Ω
maximum possible voltage across the battery pack). Diode D2 prevents the batteries from discharging through
the divider network when the charger is shut down.
PGND
12
2
3
D2
R3
MBRS340T3
0.1Ω VOUT
8
7
C6
0.01µF
VBAT
4 CELLS
R4
274k
1%
9
14
Q2
Si9410DY
D1
MBRS140T3
R5
49.9k
1%
+
C8
220µF
10V
C7
100pF
C1 (Ta)
C3 AVX (Ta) TPSD226K025R0100 ESR = 0.100 I RMS = 0.775A
C8 AVX (Ta) TPSE227M010R0100 ESR = 0.100I RMS = 1.149A
Q1 SILICONIX PMOS BV DSS = 20V RDSON = 0.125Ω CRSS = 400pF Qg = 25nC θJA = 50°C/W
Q2 SILICONIX NMOS BV DSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 50nC θJA = 50°C/W
D1, D2 MOTOROLA SCHOTTKY VBR = 40V
R3 KRL SP-1/2-A1-0R100J Pd = 0.75V
L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M µ CORE
VOUT = 1.25V • (1 + R4/R5) = 8.1V
FAST CHARGE = 130mV/R3 = 1.3A
TRICKLE CHARGE = 100mA
EFFICIENCY > 90%
AN54 • F32
ALL OTHER CAPACITORS ARE CERAMIC
Figure 32. LTC1148: High Efficiency Charger Circuit
AN54-35
Application Note 54
LTC1148: High Voltage Charger Circuit
Figure 33 is a variation of Figure 32. It is designed to
charge 6 cells and uses the LTC1148HV for higher input
voltages. R4 value has been changed to provide 12.3V
output when the battery is not connected.
VIN
12V TO
18V
+
+
C1
1µF
C2
0.1µF
3
VIN
0V = NORMAL
> 1.5A = SHUTDOWN
10
PDRIVE
R1
51Ω
“1”
TRICKLE
CHARGE
Q3
VN2222LL
R2
1k
C4
3300pF
X7R
4
C5
200pF
NPO
1
SENSE –
VFB
CT
NDRIVE
SGND
11
PGND
12
2
3
D2
R3
MBRS340T3
0.1Ω VOUT
8
7
C6
0.01µF
VBAT
6 CELLS
R4
442k
1%
9
14
Q2
Si9410DY
D1
MBRS140T3
+
R5
49.9k
1%
C8
100µF
16V
×2
C7
100pF
C1 (Ta)
C3 AVX (Ta) TPSD226K035R0200 ESR = 0.200 I RMS = 0.663A
C8 AVX (Ta) TPSE107M016R0100 ESR = 0.100I RMS = 1.149A
Q1 SILICONIX PMOS BV DSS = 20V RDSON = 0.125Ω CRSS = 400pF Qg = 25nC θJA = 50°C/W
Q2 SILICONIX NMOS BV DSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 50nC θJA = 50°C/W
D1, D2 MOTOROLA SCHOTTKY VBR = 40V
R3 KRL SP-1/2-A1-0R100J Pd = 0.75V
L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M µ CORE
VOUT = 1.25V • (1 + R4/R5) = 12.3V
FAST CHARGE = 120mV/R3 = 1.3A
TRICKLE CHARGE = 100mA
EFFICIENCY > 90%
ALL OTHER CAPACITORS ARE CERAMIC
Figure 33. LTC1148: High Voltage Charger Circuit
AN54-36
L1
50µH
4
LTC1148HV
ITH
1
Q1
Si9430DY
SHUTDOWN
SENSE +
6
C3
22µF × 2
35V
AN54 • F33
Application Note 54
3.3V/2A in a regular buck configuration. The other section
is configured in the same way as the battery charger from
Figure 32. It is powered from a wall adapter and provides
the battery with fast or trickle charging rate. When the
adapter is not connected, D3 prevents the battery from
discharging through the R2/R1 divider network.
LTC1142A: High Efficiency Power Supply Providing
3.3V/2A with Built-In Battery Charger
Figure 34 implements a high efficiency step-down converter with a built-in battery charger using a single IC. One
section of the dual LTC1142A is used to convert 4-cells to
VIN
8V TO 18V
FROM WALL ADAPTER
+
D3
MBRS340T3
RSENSE1
0.1Ω
0V = CHARGE ON
>1.5V = CHARGE OFF
+
CIN1
22µF
35V
×2
0.22µF
P-CH
Si9430DY
23
L1
50µH
24
VIN1
17
3
SHUTDOWN 1
PDRIVE2
PDRIVE1
SENSE + 2
SENSE + 1
R2
274k
1%
R1
49.9k
1%
2
6
N-CH
Si9410DY
LTC1142A
SENSE – 1
VFB2
NDRIVE1
NDRIVE2
PGND1 SGND1 CT1
5
4
25
100pF
COILTRONICS CTX50-4
COILTRONICS CTX25-4
KRL SL-C1-1/2-1R100J
KRL SL-C1-1/2-1R050J
SENSE – 2
VFB1
ITH1
27
CT1
200pF
“1” FOR TRICKLE CHARGE
ITH2
13
CT2
SGND2 PGND2
11
RC1
1k
RC2
1k
CC1
3300pF
CT2
CC2
3300pF 330pF
VN2222LL
L1
L2
RSENSE1
RSENSE2
L2
25µH
9
RSENSE2
0.05Ω
VOUT2
3.3V/2A
15
1000pF
28
D1
MBRS140T3
VBATT
4 CELLS
NiCAD
P-CH
Si9433DY
10
VIN2
SHUTDOWN 2
1000pF
+
CIN2
22µF
25V
×2
0.22µF
1
COUT1
220µF
10V
0V = OUTPUT ON
>1.5V = 3.3V OUTPUT OFF
RX
51Ω
18
19
14
16
+
20
N-CH
Si9410DY
D2
MBRS140T3
R4
84.5k
1%
COUT2
220µF
10V
×2
R3
51k
1%
100pF
FAST CHARGE = 130mV/RSENSE1 = 1.3A
TRICKLE CHARGE = 130mV/RSENSE1 = 100mA
AN54 • F34
Figure 34. LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger
AN54-37
Application Note 54
LTC1149: Dual Output Buck Converter
at the 3.3V output. The transformer used in this example
is a standard product (see the parts list). A circuit board
has been laid out for this circuit and has subsequently
been thoroughly tested under full operating conditions
and optimized for mass production requirements. A Gerber file for the board is available upon request.
The circuit shown in Figure 35A implements the most
elegant approach for dual output regulators that provide
3.3V and 5V outputs. It uses a single LTC1149. The
synchronous rectification feature of this chip is used to
provide excellent efficiency, as well as good cross regulation between the two outputs. Maximum output power of
the converter is 17W, which may be drawn in any combination between 3.3V and 5V outputs.
100
98
96
VIN
6V TO
24V
VIN = 6V
94
EFFICIENCY (%)
A regular buck regulator is used for producing 3.3V output
with T1’s primary in place of the buck inductor. The
secondary of T1 forms a boost winding for 5V output. The
transformer is wound with a simple trifilar winding to
ensure that the primary is closely coupled to the secondary. Superior cross regulation is achieved by the close
primary-to-secondary coupling and by splitting voltage
feedback paths (resistors R1 and R2 provide feedback
signals from both 3.3V and 5V outputs). Diodes D1, D2
and capacitor C7 comprise a soft-start circuit that causes
the output voltage to increase slowly when the power is
first applied to the circuit. This circuit prevents overshoot
92
VIN = 12V
90
88
VIN = 20V
86
84
82
80
0
2
4
6
8 10 12 14
TOTAL POWER OUTPUT
16
18
AN54 • F35B
Figure 35B. LTC1149: Dual Output Buck Converter
Measured Efficiency
BOLD LINES INDICATE HIGH CURRENT PATHS (SHORT LEADS)
+ C5
+ C6
22µF
+ C17
22µF
+ C18
22µF
22µF
C19
0.1µF
D3
BAS16
QP1
Si9435DY
4
QP2
Si9435DY
2
10
15
6
PDRIVE
CT
R5
24.9k
1%
R4
1k
1
TP1
4
C12
56pF
12
14
4
3
220µF
+ C4
D5
MBRS140
4
R3
0.02Ω
220µF
QN2
Si9410DY
3.3V
OUT
R8
33k
QN1
Si9410DY
+ C15
+ C1
D6
BAS16
D1
BAS16
C7
10µF
+ C3
•
6
C20
1µF
11
11 T
•2
11 T
R6
100Ω
C14
R7
1000pF 100Ω
5V
OUT
5
•
11 T
C9
0.047µF
S/D2
C8
0.068µF
C13
2.2µF
C11
1000pF
PGATE
13
ITH LTC1149 NGATE
9
3
VO(REG)
SENSE +
8
5
VI(REG)
SENSE –
16
CAP
PGND RGND SGND
7
C10
2200pF
1
VIN
S/D1/VFB
T1
HL-8700
220µF
D4
MBRS140
+ C2
220µF
220µF
+ C16
220µF
R1
102k
1%
D2
BAS16
R2
124k
1%
+
– VOUT
–VIN
AN54 • F35A
C3, C4, C15, C16
C5, C6, C8, C17
R3
T1
AVX (Ta) TPSE227M010R 49BCPA
AVX (Ta) TPSE226M035R 49BCPA
IRC LR512-01-R020F
HURRICANE, HL-8700
Figure 35A. Single LTC1149: Dual Output Buck Converter
AN54-38
Application Note 54
100
LTC1148: Constant Frequency Buck Converters
95
Finally, Figures 36A and 37A show circuits that completely
satisfy the demand in ultra-high efficiency converters
operating synchronously with an external clock. The rising
edge of the clock saturates Q3 pulling pin 4 below the
internal comparator threshold. The internal logic assumes
the end of the off-time, and turns Q1 on. Now the LTC1148
operates as a conventional constant frequency current
mode controller and therefore requires slope compensation. Q2 generates an artificial ramp signal that is superimposed on the inductor current waveform sensed by the
shunt R7. This is a standard technique to eliminate
subharmonic oscillation, a phenomenon that occurs under simultaneous conditions of fixed frequency and fixed
amplitude of inductor current when the duty cycle exceeds
50%. Subharmonic oscillations are not related to the
closed-loop transfer function.
VIN = 8V
EFFICIENCY (%)
90
85
VIN = 15V
80
75
70
65
1
OUTPUT CURRENT (A)
0.1
10
AN54 • F36B
Figure 36B. LTC1148: (8V-15V to 5V/2A)
Constant Frequency Buck Converter
Measured Efficiency
VIN
8V TO 15V
+
C2
0.1µF
C3
1µF
+
U1
R10
510k
3
10
> 1.5V = SHUTDOWN
6
R6
1k
4
C6
200pF
C5
6800pF
11
PDRIVE
VIN
SHUTDOWN
LTC1148-5
SENSE +
ITH
SENSE –
CT
NDRIVE
SGND
PGND
1
Q1
Si9430DY
8
7
C8
1000pF
C4
51pF
OSC IN
200kHz
R4
100Ω
R5
750Ω
Q3
2N2222
Q4
Si9410DY
AVX (Ta) TPSD226K025R0200
AVX (Ta) TPSE227K010R0080
COILTRONICS CTX15-4
KRL SL-1-C1-0R040J PD = 1W
L1
15µH
R7
0.04Ω
D3
MBR130T3
R9
100Ω
+
VOUT
5V
2A
C9
220µF
10V
12
OPERATION BEYOND SPECIFIED INPUT VOLTAGE CAN CAUSE
INSTABILITY. EXTERNAL OSCILLATOR INPUT: TTL LEVEL.
FOR APPLICATIONS WITH VIN > 2VOUT SLOPE COMPENSATION
CAN BE DELETED.
C7
C9
L1
R7
R8
100Ω
14
D2
1N4148
R3
220Ω
C7
22µF
25V
×2
D4
1N4148
Q2
2N2222
D1
1N4148
R2
5.1k
R1
30k
C1
100pF
SLOPE COMPENSATION
AN54 • F36A
Figure 36A. LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter
AN54-39
Application Note 54
100
If the input voltage always exceeds twice the output (duty
cycle in this case would be less than 50%) the circuit inside
the dashed box can be omitted. Resistor R11 is added to
the circuit of disable Burst Mode operation ensuring true
in-sync operation over the full range of output current. The
circuitry is designed to be synchronized by a 200kHz
clock to accommodate other external frequencies; nothing
more than component value changes is required. If the
input voltage goes beyond specified range, the controller
will lose synchronization (it will still regulate, however).
R10 increases input voltage pull-in range and can be
omitted if it is not required. Values above 430k ensure
proper start-up.
4.5V TO 3.3V/2A
95
EFFICIENCY (%)
90
85
6.5V TO 3.3V/2A
80
75
70
65
1
OUTPUT CURRENT (A)
0.1
10
AN54 • F37B
Figure 37B. LTC1148: (4.5V-6.5V to 3.3V/2A)
Constant Frequency Buck Converter
Measured Efficiency
VIN
4.5V TO 6.5V
+
C2
0.1µF
C3
1µF
+
U1
R10
470k
3
10
> 1.5V = SHUTDOWN
6
R6
100Ω
4
C6
150pF
C5
3300pF
11
PDRIVE
VIN
SHUTDOWN
SENSE +
ITH
LTC1148-3.3
SENSE –
CT
NDRIVE
SGND
PGND
1
Q1
Si9430DY
8
7
OSC IN
200kHz
R4
100Ω
R5
750Ω
Q3
2N2222
R7
0.04Ω
14
Q4
Si9410DY
D3
MBR130T3
R9
100Ω
C9
220µF
10V
D4
1N4148
OPERATION BEYOND SPECIFIED INPUT VOLTAGE CAN CAUSE
INSTABILITY. EXTERNAL OSCILLATOR INPUT: TTL LEVEL.
C7 AVX (Ta) TPSD226K025R0200
C9 AVX (Ta) TPSE227K010R0080
L1 COILTRONICS CTX15-4
R7 KRL SL-1-C1-R040J PD = 1W
Q2
2N2222
R11
18k
R1
20k
D1
1N4148
R2
2.2k
C1
100pF
SLOPE COMPENSATION
Figure 37A. LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter
AN54-40
+
VOUT
3.3V
2A
12
D2
1N4148
C4
50pF
R8
100Ω
L1
15µH
C8
1000pF
C7
22µF
25V
×2
AN54 • F37A
Application Note 54
APPENDIX A
TOPICS OF COMMON INTEREST
Defeating Bust Mode Operation
Sometimes applications require Burst Mode operation to
be defeated. It might be useful in a high output current
circuit which never operates at light loads. Ensuring
continuous operation in this case usually improves the
circuit noise immunity and helps to eliminate audible noise
from certain types of inductors when they are lighter
loaded. The Burst Mode operation should be disabled if an
overwinding is used to provide boosted voltage, additional
to the main output (for example, see Figure 30A). This
allows to draw power from the secondary with improved
cross-regulation, even if the primary output is not loaded.
Defeating of Burst Mode operation should also be considered when the fixed frequency circuits from Figures 36A
and 37A are used. With continuous operation these circuits always operate fully synchronized to the external
clock.
Whatever the reason, Burst Mode operation can be suppressed with a simple external network which cancels the
25mV minimum current comparator threshold. An external offset is put in series with the SENSE – pin to subtract
from the built-in 25mV offset. An example of this technique is shown in Figure A1.
L
33µH
LTC1148
FAMILY
SENSE
+
RSENSE
0.05Ω
VOUT
5V
2A
R2
100Ω
100pF
SENSE –
R1
R3 100Ω
20k
AN54 • FA01
Figure A1. Defeating Burst Mode
Two 100Ω resistors are inserted in series with the leads
from the sense resistor. With the addition of R3, a current
is generated through R1 causing an offset of:
 R1 
VOFFSET = VOUT × 

 R1 + R3 
If VOFFSET exceeds 25mV the minimum threshold will be
cancelled and Burst Mode operation is prevented from
occurring. Since the offset voltage is constant, the maximum load current is also decreased. Thus to get back to
the same output current, the sense resistor must be lower:
RSENSE =
75mV
IMAX
Soft-Start Circuits
Right after the power-on, the regulator operates in a shortcircuit condition while charging output capacitors. With
earlier voltage mode converters, this led to enormous
current transient at start-up. Soft-start circuits were usually added to fix this problem. The LTC1148 series
implements current mode technique which inherently
provides current limiting and does not require any special
soft-start circuits. Start-up current is limited to the shortcircuit current value of 150mV/RSENSE.
Some applications might, however, require softer start. It
helps to avoid output overshoot when the power is first
applied to the circuit, and it also prevents the input
supply’s overcurrent protection from latching, when the
input voltage increases slowly. Figures A2 and A3 provide
possible solutions for soft-start. Capacitor C1 in Figure A2
holds down ITH pin limiting the output current. C1 is
charged via R1, when the voltage across its terminals
exceeds DC level of ITH pin, D2 becomes reverse-biased
and the capacitor no longer has an effect on the circuit
operation. D1 provides discharge path for C1 when the
input voltage is removed. The soft-start time constant is
defined by R1 and C1.
In Figure A3, capacitor C1 holds down the SENSE – pin
providing additional offset to the current comparator. C1
charges through D1 and R2, slowly increasing maximum
operating current. When C1 is fully charged D1 is reversebiased and the capacitor no longer affects the operation.
AN54-41
Application Note 54
D2 provides a discharge path for C1 when the output
voltage disappears. The soft-start time constant is defined
by R2 and C1.
VIN
VIN
D1
1N4148
R1
22k
LTC1148
FAMILY
D2
MBR0520L
ITH
C1
4.7µF
16V
+
R2
1k
C2
3300pF
AN54 • FA02
Figure A2. Soft-Start Circuit with ITH Pin Clamping
L
33µH
LTC1148
FAMILY
SENSE
+
SENSE
–
RSENSE
0.05Ω
R1
100Ω
+
C2
1000pF
R2
100Ω
D1
1N4148
D2
1N4148
C1
10µF
10V
The simplest approach uses load step transient by switching in an additional load resistor and simultaneously
monitoring the output. Switching regulators take several
cycles to respond to a step in resistive load current. When
a load step occurs, output voltage shifts by an amount
equal to ∆ILOAD × ESR, where ESR is the output capacitor
effective series resistance. Load current change also begins to charge or discharge output capacitor until the
regulator loop adapts to the current change and returns
VOUT to its steady state value. If during this recovery time
VOUT has ringing, it indicates a stability problem, and the
capacitor at ITH pin should be increased.
A simple dynamic load circuit is shown in Figure A4 where
the MOSFET Q1, driven by an external generator, switches
a load resistor R2 in and out. The generator should provide
10V gate drive (not a TTL level). The drive signal frequency
is not critical. A good starting point is 500Hz and the load
change from 50% to the full load.
VOUT
5V
2A
LTC1148
FAMILY
AN54 • FA03
+
COUT
R1
GENERATOR
IN (10VP-P)
R2
Q1
IRFZ44
100k
(HEAD SINK MAY
BE REQUIRED)
Figure A3. Soft-Start Circuit with Sense Pin Clamping
AN54 • FA04
Figure A4. Simple Dynamic Load
Frequency Compensation
The LTC1148 family of regulators contains both voltage
and current loops, which, together with external capacitors and inductors, require a pretty complex mathematical
approach to frequency compensation. Operating point
changes with input voltage and output current variations
add complications and suggest a more practical empirical
method.
AN54-42
The LTC1148 series regulators provide a very stable
operation. The compensation values used in the circuits in
this note have been tested over the wide range of operating
conditions and proved to provide an adequate compensation for most applications. Usually no stability testing, as
described above, is required.
Application Note 54
APPENDIX B
SUGGESTED MANUFACTURERS
Linear Technology provides this list of manufacturers to
get you started in your component selection process. We
make no claims about any of these companies except that
they provide components necessary in switching power
supplies. There are many more companies to choose
from; for a more complete list refer to the PCIM Buyer’s
Philips Components
1440 W. Indian Town Rd.
Jupiter, FL 33458
(407) 744-4200
Cer., Chip Capacitors
Batteries
Duracell
OEM Sales & Marketing
Berkshire Industrial Park
Bethel, CT 06801
(800) 431-2656
Murata Erie North America
1900 W. College Ave.
State College, PA 16801
(814) 237-1431
Eveready Battery Co.
Checkerboard Square
St. Louis, MO 63164
(314) 982-2000
Nichicon (America) Corporation
927 East State Parkway
Schaumburg, IL 60173
(708) 843-7500
Aluminum Electrolytic
Bipolar Transistors
Motorola Inc.
3102 North 56th St.
MS 56-126
Phoenix, AZ 85018
(800) 521-6274
Full Line
Zetex
87 Modular Ave.
Commack, NY 11725
(516) 543-7100
High Gain Bipolar Switching Transistors
including Surface Mount Devices
Capacitors
AVX Corporation
P.O. Box 867
Myrtle Beach, SC 29578
(803) 946-0690
Tant., Cer., Surface Mount
Elpac
1567 Reynolds Ave.
Irvine, CA 92714
Film Capacitors
(714) 476-6070
Film Capacitors
Intertechnical Group
2269 Saw Mill River Rd., Bldg. 4C
P.O. Box 217
Elmsford, NY 10523
(914) 347-2474
Polycarbonate Film
Guide. PCIM (Power Conversion & Intelligent Motion) is
published by Intertec International Inc., 2472 Eastman
Ave., Bldg. 33-34, Ventura, California 93003-5774, (805)
650-7070. PCIM is free to qualified applicants. Back
issues, such as the Buyer’s Guide can be purchased.
Sanyo Video Components (USA) Corp.
2001 Sanyo Ave.
San Diego, CA 92173
(619) 661-6835
Low ESR Filter Capacitors-Solid Aluminum
Electrolytic Capacitors (OS-CON)
Sprague
678 Main St.
P.O. Box 231
Sanford, ME 04073
(207) 324-4140
Tantalum Capacitors
Current Sense Resistors
Dale Electronics
1122 23rd St.
P.O.Box 609
Columbus, NE 68602
(402) 564-3131
Resistors, Inductors, Xformers
Diodes
Fuji/Collmer
14368 Proton Rd.
Dallas, TX 75244
(214) 233-1589
Low Current Schottkys
General Instruments
10 Melville Park Rd.
Melville, NY 11747
(516) 847-3222
Motorola Inc.
5005 E. McDowell Rd.
P.O. Box 2953
Phoenix, AZ 85062
(602) 244-5768
Diodes
Philips Components Disc. Prod. Div.
100 Providence Pike
Slatersville, RI 02876
(401) 762-3800
Discrete Semi Group
Ferrite Beads
Fair-Rite Products Corp.
1 Commerial Row
P.O. Box J
Wallkill, NY 12589
(914) 895-2055
Toshiba America Elec. Components
9775 Toledo Way
Irvine, CA 92718
(714) 455-2000
IRC
4222 South Staples St.
Corpus Christi, TX 78411
(512) 992-7900
Heat Sinks
Aavid Engineering, Inc.
One Kool Path Box 400
Laconia, NH 03247
(603) 528-3400
KRL
160 Bouchard St.
Manchester, NH 03103
(603) 668-3210
Int’l Electronic Research Group
135 W. Magnolia Blvd.
Burbank, CA 91502
(213) 849-2481
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
AN54-43
Application Note 54
Thermalloy
2021 W. Valley View Lane
Dallas, TX 75234
(214) 243-4321
Toko America Incorporated
1250 Feehanville Dr.
Mount Propsect, IL 60056
(708) 635-3200
Inductors and Transformers
Beckman Industrial Corp.
4200 Bonita Place
Fullerton, CA 92635
(714) 447-2345
Inductors, Xformers including SMT
Magnetic Materials
Fair-Rite Products Corp.
1 Commercial Row
P. O. Box J
Wallkill, NY 12589
(914) 895-2055
Ferrite
Caddell-Burns
258 East Second St.
Mineola, NY 11501
(516) 746-2310
Micrometals, Inc.
1190 N. Hawk Circle
Anaheim, CA 92807
(800) 356-5977
Powdered Iron
Coilcraft
1102 Silver Lake Rd.
Cary, IL 60013
(800) 322-2645
Coiltronics
6000 Park of Commerce Blvd.
Boca Raton, FL 33487
(407) 241-7876
Full Line including Surface Mount Inductors
Dale Electronics
E. Highway 50
P. O. Box 180
Yankton, SD 57078
(605) 665-9301
Inductors, Xformers including SMT
Gowanda Electronics Corp.
1 Industrial Place
Gowanda, NY 14070
(716) 532-2234
Hurricane Electronics Lab
P.O. Box 1280
Hurricane, UT 84737
(801) 635-2003
Murata Erie North America
2200 Lake Park Drive
Smyrna, GA 30080
(404) 436-1300
Renco
60 E. Jefryn Blvd.
Deerpark, NY 11729
(516) 586-5566
Sumida Electronic
5999 New Wilke Rd., Ste. 110
Rolling Meadows, IL 60008
(708) 956-0666
TDK Corp. of America
1600 Feehanville Dr.
Mount Prospect, IL 60056
(708) 803-6100
AN54-44
Magnetics Div. Spang & Co
P.O. Box 391
Butler, PA 16003-0391
(412) 282-8282
Molypermalloy, Kool Mµ, Ferrite
Philips Components Disc. Prod. Div.
Materials Group
1033 King Highway
Saugerties, NY 12477
(914) 246-2811
Ferrite
Pyroferric International, Inc.
200 Madison St.
Toledo, IL 62468
(217) 849-3300
Powdered Iron
Siemens Components, Inc.
186 Wood Ave. South
Iselin, NJ 08830
(908) 906-4300
Ferrite
TDK Corp. of America
1600 Feehanville Dr.
Mount Prospect, IL 60056
(708) 803-6100
Ferrite
Mounting Hardware
Bergquist
5300 Edina Industrial Blvd.
Minneapolis, MN 55439
(612) 835-2322
Thermally Conductive Insulators
Thermalloy
2021 W. Valley View Lane
Dallas, TX 75234
(214) 243-4321
Power Sockets, Thermal Compounds,
and Adhesives Thermally Conductive
Insulators, Mounting Kits
Power MOSFETs
International Rectifier Corp.
233 Kansas St.
El Segundo, CA 90245
(310) 322-3331
Motorola Inc.
5005 E. McDowell Rd.
Phoenix, AZ 85008
(602) 244-3576
Siliconix
2201 Laurelwood Rd.
Santa Clara, CA 96056
(800) 554-5565
Resistors
Micro-Ohm Corp.
1088 Hamilton Rd.
Duarte, CA 91010
(818) 357-5377
Thermo Disc
1981 Port City Blvd.
Muskegon, MI 49443
(616) 777-2602
RCD Components, Inc.
520 East Industrial Park Dr.
Manchester, NH 03109
(603) 669-0054
Caddock Electronics
1717 Chicago Ave.
Riverside, CA 92507-2364
(909) 788-1700
Wire
Belden Wire & Cable
P.O. BOX 1980
Richmond, IN 47375
(317) 983-5200
Stockwell Rubber
4749 Tolbut St.
Philadelphia, PA 19136
(800) 523-0123
Thermally Conductive Insulators
Linear Technology Corporation
LT/GP 1094 5K REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1993