XR79206
40V, 6A Synchronous Step-Down
COT Power Module
Description
FEATURES
■■ 6A step-down power module
5V to 40V wide single input voltage
≥0.6V adjustable output voltage
■■ Controller, drivers, inductor, passive
components and MOSFETs integrated in
one package
■■ Proprietary constant on-time control
No loop compensation required
Stable with ceramic output capacitors
Programmable 100ns to 1µs on-time
Constant 400kHz to 800kHz frequency
Selectable CCM or DCM/CCM
operation
■■ Precision enable and power-good flag
■■ Programmable soft-start
■■ 10mm x 10mm x 4mm QFN package
The XR79206 is part of a family of 40V synchronous step-down
power modules combining the controller, drivers, inductor, passive
components and MOSFETs in a single package for point-of-load
supplies. This module requires very few external components leading
to ease of design and fast time to market. The XR79206 has load
current rating of 6A. A wide 5V to 40V input voltage range allows for
single supply operation from industry standard 24V ±10%, 18V to 36V
and rectified 18VAC and 24VAC rails.
With a proprietary emulated current mode Constant On-Time (COT)
control scheme, the XR79206 provides extremely fast line and load
transient response using ceramic output capacitors. It requires no
loop compensation, simplifying circuit implementation and reducing
overall component count. The control loop also provides 0.2% load
and 0.1% line regulation and maintains constant operating frequency.
A selectable power saving mode, allows the user to operate in
Discontinuous Current Mode (DCM) at light current loads significantly
increasing the converter efficiency.
APPLICATIONS
■■ Drones and remote vehicles
■■ Automotive displays
■■ FPGA/DSP/processor supplies
■■ Industrial control and automation
■■ Telecommunications and infrastructure
equipment
■■ Distributed power architecture
A host of protection features, including overcurrent, over temperature,
short-circuit and UVLO, help achieve safe operation under abnormal
operating conditions.
The XR79206 is available in a RoHS-compliant, green/halogen-free
space-saving 10mm x 10mm x 4mm QFN package.
Typical Application
100
VIN
VIN
PVIN
EN/MODE
90
PGOOD
Efficiency (%)
VOUT
POWER GOOD
VOUT
CFF
CIN
VCC
RPGOOD
XR79206
SS
TON
CVCC
CSS
RON
700kHz
95
ENABLE/MODE
SW
ILIM
AGND
PGND
RLIM
RFF
RFB1
COUT
FB
RFB2
85
80
70
12.0V
5.0V
3.3V
1.8V
65
60
Figure 1. Typical Application
500kHz
75
0
1
2
3
IOUT (A)
4
5
6
Figure 2. Efficiency, 24VIN
REV1B
1/19
XR79206
Absolute Maximum Ratings
Operating Conditions
These are stress ratings only and functional operation
of the device at these ratings or any other above those
indicated in the operation sections of the specifications
below is not implied. Stresses beyond those listed under
absolute maximum ratings may cause permanent damage
to the device. Exposure to any absolute maximum rating
condition for extended periods may affect device reliability
and lifetime.
PVIN, VIN................................................................5V to 40V
Package power dissipation max at 25°C...................... 5.5W
PVIN, VIN.......................................................................... -0.3V to 43V
Package thermal resistance θJA............................ 18.1°C/W
VCC...................................................................................-0.3V to 6.0V
NOTES:
1. No external voltage applied.
2. SW pin’s DC range is -1V, transient is -5V for less than 50ns.
3. Recommended frequency for optimum performance.
BST.................................................................-0.3V to 48V(1)
SW, ILIM ........................................................ -1V to 40V(1)(2)
PGOOD, VCC, TON, SS, EN, FB.................... -0.3V to 5.5V
Switching frequency................................. 400kHz-800kHz(3)
Junction temperature range (TJ).................. -40°C to 125°C
BST-SW.............................................................. -0.3V to 6V
SW, ILIM......................................................... -1V to 43V(1)(2)
All other pins.......................................... -0.3V to VCC + 0.3V
Storage temperature..................................... -65°C to 150°C
Junction temperature.................................................. 150°C
Power dissipation....................................... Internally limited
Lead temperature (soldering, 10 seconds)................. 300°C
ESD rating (HBM – human body model)........................ 2kV
ESD rating (CDM – charged device model)................... 2kV
Electrical Characteristics
TJ = 25°C, VIN = 24V, BST = VCC, SW = AGND = PGND = 0V, CVCC = 4.7μF, unless otherwise specified. Limits applying
over the full operating temperature range are denoted by a •.
Symbol
Parameter
Conditions
•
Min
VCC regulating
•
5
Not switching, VIN = 24V, VFB = 0.7V
•
Typ
Max
Units
40
V
2
mA
Power Supply Characteristics
VIN
Input voltage range
IVIN
VIN supply current
IOFF
Shutdown current
0.7
f = 500kHz, RON = 124kΩ, VFB = 0.58V
10
mA
Enable = 0V, PVIN = VIN = 24V
1
µA
Enable and Undervoltage Lock-Out (UVLO)
VIH_EN_1
EN pin rising threshold
VEN_HYS_1
EN pin hysteresis
VIH_EN_2
EN pin rising threshold for DCM/
CCM
VEN_HYS_2
EN pin hysteresis
VCC UVLO start threshold
•
1.8
1.9
2.0
70
•
2.8
3.0
mV
3.1
110
Rising edge
•
VCC UVLO hysteresis
•
REV1B
4.00
4.25
195
V
V
mV
4.40
V
mV
2/19
XR79206
Electrical Characteristics (Continued)
TJ = 25°C, VIN = 24V, BST = VCC, SW = AGND = PGND = 0V, CVCC = 4.7μF, unless otherwise specified. Limits applying
over the full operating temperature range are denoted by a •.
Symbol
Parameter
Conditions
•
Min
Typ
Max
Units
0.596
0.600
0.604
V
0.594
0.600
0.606
V
Reference Voltage
VREF
Reference voltage
DC load regulation
DC line regulation
VIN = 5V to 40V, VCC regulating
•
CCM operation, closed loop, applies to
any COUT
±0.2
%
±0.1
%
120
ns
Programmable Constant On-Time
TON(MIN)
Minimum programmable on-time
RON = 14kΩ, VIN = 40V
TON1
On-time 1
RON = 14kΩ, VIN = 24V
•
180
200
220
ns
TON2
On-time 2
RON = 35.7kΩ, VIN = 24V
•
420
470
520
ns
On-time 2 frequency
RON = 35.7kΩ, VIN = 24V, VOUT = 5.0V, IOUT = 6A
425
470
525
kHz
250
350
ns
TOFF(MIN)
Minimum off-time
•
Diode Emulation Mode
Zero crossing threshold
DC value measured during test
-2
mV
Soft-Start
SS charge current
SS discharge current
•
-14
-10
-6
µA
Fault present
•
1
VIN = 6V to 40V, ILOAD = 0 to 30mA
•
4.8
5.0
VIN = 5V, ILOAD = 0 to 20mA
•
4.51
4.8
-10
-7
-5
%
1.5
4
%
mA
VCC Linear Regulator
VCC output voltage
5.2
V
Power Good Output
Power good threshold
Power good hysteresis
Power good sink current
1
REV1B
mA
3/19
XR79206
Electrical Characteristics (Continued)
TJ = 25°C, VIN = 24V, BST = VCC, SW = AGND = PGND = 0V, CVCC = 4.7μF, unless otherwise specified. Limits applying
over the full operating temperature range are denoted by a •.
Symbol
Parameter
Conditions
•
Min
Typ
Max
Units
Protection: OCP, OTP, Short-Circuit
Hiccup timeout
110
ILIM/RDS
2.40
ILIM current temperature
coefficient
2.85
ms
3.20
0.4
ILIM comparator offset
•
-8
0
µA/mΩ
%/°C
8
mV
Current limit blanking
GL rising >1V
100
ns
Thermal shutdown threshold
Rising temperature
150
°C
15
°C
Thermal hysteresis
Feedback pin short-circuit
threshold
Percent of VREF, short circuit is active.
After PGOOD is asserted
•
50
60
70
%
41
59
mΩ
17.6
21.5
mΩ
Output Power Stage
RDSON
High-side MOSFET RDSON
Low-side MOSFET RDSON
IOUT
Maximum output current
L
Output inductance
CIN
Input capacitance
CBST
Bootstrap capacitance
IDS = 2A
•
6
1.8
REV1B
A
2.2
2.6
μH
1
μF
0.1
μF
4/19
XR79206
1
2
FB
3
AGND
AGND
AGND
ILIM
BST
BST
PVIN
PVIN
PVIN
PVIN
PVIN
PVIN
PVIN
PVIN
NC
PGND
PGND
PGND
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
EN/MODE
71
SS
PGOOD
70
TON
72
Pin Configuration
PGND
52
PGND
51
PGND
4
50
VOUT
AGND
5
49
VOUT
VIN
6
48
VOUT
VCC
7
47
VOUT
PGND
8
46
VOUT
SW
9
45
VOUT
44
VOUT
43
VOUT
SW 12
42
VOUT
PGND 13
41
VOUT
PGND 14
40
VOUT
39
VOUT
PGND 16
38
VOUT
PGND 17
37
VOUT
PGND
PAD 2
SW
PAD
SW 10
VOUT
PAD
SW 11
VOUT 35
VOUT 34
VOUT 33
VOUT 32
VOUT 31
SW 30
SW 29
SW 28
SW 27
SW 26
SW 25
SW 24
PGND 23
PGND 22
PGND 21
PGND 19
PGND 18
PGND 20
PGND
PAD 1
PGND 15
VOUT 36
53
PVIN
PAD
BST
PAD
AGND
PAD
Pin Functions
Pin Number
Pin Name
Type
Description
1
SS
A
2
PGOOD
OD, O
3
FB
A
Feedback input to feedback comparator. Connect with a set of resistors to VOUT and AGND in order to
program VOUT.
4, 5, 69, 70,
AGND Pad
AGND
A
Analog ground. Control circuitry of the IC is referenced to this pin. Connect to PGND.
6
VIN
PWR
IC supply input. Provides power to internal LDO. Connect to PVIN pins.
7
VCC
PWR
The output of LDO. Bypass with a 4.7μF capacitor to AGND.
8
PGND
PWR
Controller low-side driver ground. Connect with a short trace to closest PGND pins or PGND pad.
13-23, 51-56,
PGND Pads
PGND
PWR
Ground of the power stage. Should be connected to the system’s power ground plane.
9-12, 24-30,
SW Pad
SW
PWR
Switching node. It internally connects the source of the high-side FET, the drain of the low-side FET,
the inductor and bootstrap capacitor. Use thermal vias and/or sufficient PCB land area in order to heatsink
the low-side FET and the inductor.
31-50,
VOUT Pad
VOUT
PWR
Output of the power stage. Place the output filter capacitors as close as possible to these pins.
58-65,
PVIN Pad
PVIN
PWR
Power stage input voltage. Place the input filter capacitors as close as possible to these pins.
66, 67,
BST Pad
BST
A
Controller high-side driver supply pin. It is internally connected to SW via a 0.1μF bootstrap capacitor.
Leave these pins floating.
68
ILIM
A
Overcurrent protection programming. Connect with a short trace to SW pins.
71
EN/MODE
I
Precision enable pin. Pulling this pin above 1.9V will turn the IC on and it will operate in Forced CCM. If the
voltage is raised above 3.0V, then the IC will operate in DCM or CCM depending on load.
72
TON
A
Constant on-time programming pin. Connect with a resistor to AGND.
Soft-start pin. Connect an external capacitor between SS and AGND to program the soft-start rate based
on the 10μA internal source current.
Power-good output. This open-drain output is pulled low when VOUT is outside the regulation.
NOTE:
A = Analog, I = Input, O = Output, OD = Open Drain, PWR = Power.
REV1B
5/19
Typical Performance Characteristics
3.350
3.350
3.340
3.340
3.330
3.330
3.320
3.320
3.310
3.310
VOUT (V)
VOUT (V)
TA = 25°C, VIN = 24V, VOUT = 3.3V, IOUT = 6A, f = 500kHz, unless otherwise specified. Schematic shown in Figure 27.
3.300
3.290
3.300
3.290
3.280
3.280
3.270
3.270
3.260
3.260
3.250
0
1
2
3
4
5
3.250
6
5
10
15
20
Figure 3. Load Regulation
800
40
35
40
Calculated
Typical
700
700
600
600
500
tON (ns)
tON (ns)
35
800
Calculated
Typical
900
500
400
300
400
300
200
200
100
0
10
20
30
40
RON (kΩ)
50
60
100
70
5
Figure 5. tON vs. RON
700
700
600
600
500
500
f (kHz)
800
400
300
200
200
100
100
1.0
2.0
3.0
IOUT (A)
4.0
15
20
25
VIN (V)
30
400
300
0.0
10
Figure 6. tON vs. VIN, RON = 14kΩ
800
0
30
Figure 4. Line Regulation
1,000
0
25
VIN (V)
IOUT (A)
f (kHz)
)
XR79206
5.0
0
6.0
5
10
15
20
25
30
35
40
VIN (V)
Figure 7. Switching Frequency vs. IOUT
Figure 8. Switching Frequency vs. VIN
REV1B
6/19
XR79206
Typical Performance Characteristics (Continued)
TA = 25°C, VIN = 24V, VOUT = 3.3V, IOUT = 6A, f = 500kHz, unless otherwise specified. Schematic shown in Figure 27.
610
10
9
8
605
7
VREF (mV)
IOCP (A)
6
5
4
3
2
595
Calculated worst case
Typical
1
0
2
2.5
3
3.5
600
590
-40
4
-20
0
20
40
TJ (°C)
RLIM (kΩ)
Figure 9. IOCP vs. RLIM
80
100
120
Figure 10. VREF vs. Temperature
280
4.0
260
3.5
240
3.0
Inductance (μH)
220
tON (ns)
60
200
180
160
2.5
2.0
1.5
140
1.0
120
0.5
0.0
100
-40
-20
0
20
40
TJ (°C)
60
80
100
120
0
Figure 11. tON vs. Temperature, RON = 14kΩ
1
2
3
4
5
6
7
Current (A)
8
9
10
11
12
Figure 12. Inductance vs. Current
4.0
Inductor Current Ripple ∆IL(A)
3.5
500kHz
3.0
600kHz
2.5
700kHz
2.0
1.5
1.0
0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
VOUT (V)
3.5
4.0
4.5
5.0
Figure 13. Inductor Current Ripple vs. VOUT
REV1B
7/19
XR79206
Typical Performance Characteristics (Continued)
TA = 25°C, VIN = 24V, VOUT = 3.3V, IOUT = 6A, f = 500kHz, unless otherwise specified. Schematic shown in Figure 27.
SW
SW
VOUT
AC coupled 20MHz
VOUT
25mVp-p
AC coupled 20MHz
63mVp-p
IOUT
IOUT
Figure 14. Steady State CCM, IOUT = 6A
Figure 15. Steady State DCM, IOUT = 0A
VIN
VIN
EN
EN
VOUT
VOUT
IOUT
IOUT
4ms/div
4ms/div
Figure 16. Power Up, IOUT = 6A
Figure 17. Power Up, IOUT = 0A
SW
SW
VOUT
AC coupled 20MHz
VOUT
AC coupled 20MHz
148mV
100mV
156mV
Di/Dt = 2.5A/us
IOUT
148mV
Di/Dt = 2.5A/us
IOUT
20 us/div
40 us/div
Figure 18. Load Step, CCM, 0A-3A-0A
Figure 19. Load Step, DCM/CCM, 0.05A-3A-0.05A
REV1B
8/19
XR79206
Typical Performance Characteristics (Continued)
Efficiency and Package Thermal Derating
TA = 25°C, No airflow, f = 500kHz, unless otherwise specified. Schematic shown in Figure 27.
100
95
85
TAMBIENT (ºC)
Efficiency (%)
90
80
75
70
5.0V DCM
3.3V DCM
1.8V DCM
65
60
0.1
5.0V CCM
3.3V CCM
1.8V CCM
120
115
110
105
100
95
90
85
80
75
70
65
60
1.0
IOUT (A)
5.0V CCM
3.3V CCM
1.8V CCM
1.0
700kHz
85
TAMBIENT (ºC)
Efficiency (%)
90
80
75
12.0V DCM
5.0V DCM
3.3V DCM
1.8V DCM
65
60
0.1
4.0
5.0
6.0
Figure 21. Maximum TAMBIENT vs. IOUT,
VIN = 12V
100
70
3.0
IOUT (A)
Figure 20. Efficiency, VIN = 12V
95
2.0
12.0V CCM
5.0V CCM
3.3V CCM
1.8V CCM
1.0
IOUT (A)
120
115
110
105
100
95
90
85
80
75
70
65
60
700kHz
12.0V CCM
5.0V CCM
3.3V CCM
1.8V CCM
1.0
2.0
3.0
4.0
5.0
6.0
IOUT (A)
Figure 22. Efficiency, VIN = 24V
Figure 23. Maximum TAMBIENT vs. IOUT,
VIN = 24V
REV1B
9/19
XR79206
Functional Block Diagram
VCC
TON
VCC UVLO
Enable LDO
VIN
LDO
CIN
1µF
VCC
OTP
TJ
FB
0.6V
PGND
150 C
PGOOD
10µA
PVIN
Switching
Enabled
4.25V
VCC
BST
Current
Emulation &
DC Correction
VIN
On Time
SS
Switching
Enabled
FB
CBST
0.1µF
Feedback
Comparator
0.6V
R Q
S Q
PGOOD Comparator
tON
Short-Circuit Detection
0.36V
Switching
Enabled
GH
L
Dead
Time
Control
Minimum
On Time
0.555V
Zero Cross Detect
VOUT
GL
R Q
S Q
Hiccup
Mode
If Four
Consecutive OCP
1.9V
CCM or CCM/DCM
3V
VCC
Enable
Hiccup
Enable LDO
Enable LDO
EN/
MODE
SW
If 8 Consecutive
ZCD Then DCM
If 1 Non-ZCD
Then Exit DCM
OCP
Comparator
50µA
XR79206
SW
-2mV
AGND
ILIM
PGND
Figure 24. Functional Block Diagram
REV1B
10/19
XR79206
Applications Information
Functional Description
XR79206 is a synchronous step-down proprietary
emulated current-mode Constant On-Time (COT) module.
The on-time, which is programmed via RON,
is inversely proportional to VIN and maintains a nearly
constant frequency. The emulated current-mode control is
stable with ceramic output capacitors.
Each switching cycle begins with GH signal turning on
the high-side (switching) FET for a preprogrammed time.
At the end of the on-time, the high-side FET is turned off
and the low-side (synchronous) FET is turned on for a
preset minimum time (250ns nominal). This parameter is
termed minimum off-time. After the minimum off-time, the
voltage at the feedback pin FB is compared to an internal
voltage ramp at the feedback comparator. When VFB drops
below the ramp voltage, the high-side FET is turned on
and the cycle repeats. This voltage ramp constitutes an
emulated current ramp and makes possible the use of
ceramic capacitors, in addition to other capacitor types,
for output filtering.
Selecting the DCM/CCM Mode
In order to set the module operation to DCM/CCM, a voltage
between 3.1V and 5.5V must be applied to EN/MODE pin.
If an external control signal is available, it can be directly
connected to EN/MODE. In applications where an external
control is not available, EN/MODE input can be derived
from VIN. If VIN is well regulated, use a resistor divider
and set the voltage to 4V. If VIN varies over a wide range,
the circuit shown in Figure 26 can be used to generate the
required voltage for DCM/CCM operation.
Enable/Mode Input (EN/MODE)
EN/MODE pin accepts a tri-level signal that is used to control
turn on/off. It also selects between two modes of operation:
forced CCM and DCM/CCM. If EN is pulled below 1.8V,
the module shuts down. A voltage between 2.0V and 2.8V
selects the forced CCM mode which will run the module in
continuous conduction at all times. A voltage higher than
3.1V selects the DCM/CCM mode which will run the module
in discontinuous conduction at light loads.
Selecting the Forced CCM Mode
In order to set the module to operate in forced CCM, a voltage
between 2.0V and 2.8V must be applied to EN/MODE.
This can be achieved with an external control signal
that meets the above voltage requirement. Where an
external control is not available, the EN/MODE can be
derived from VIN. If VIN is well regulated, use a resistor
divider and set the voltage to 2.5V. If VIN varies over a
wide range, the circuit shown in Figure 25 can be used
to generate the required voltage. Note that at VIN of
5.0V and 40V the nominal Zener voltage is 4.0V and
5.0V respectively. Therefore for VIN in the range of 5.0V
to 40V, the circuit shown in Figure 25 will generate VEN
required for forced CCM.
VIN
RZ
10k
R1
30.1k, 1%
Zener
MMSZ4685T1G or
Equivalent
EN/MODE
R2
35.7k, 1%
Forced CCM, wide VIN range
Figure 25. Selecting Forced CCM by
Deriving EN/MODE from VIN
VIN
RZ
10k
VEN
Zener
MMSZ4685T1G or
Equivalent
EN/MODE
DCM/CCM, wide VIN range
Figure 26. Selecting DCM/CCM by
Deriving EN/MODE from VIN
REV1B
11/19
RON =
Applications Information (Continued)
Programming the On-Time
The on-time tON is programmed via resistor RON according
to following equation:
RON =
VIN × [tON – (2.5 × 10-8)]
2.95 x 10-10
A graph of tON vs. RON, using the above equation,
is compared to typical test data in Figure 5. The graph
shows that calculated dataVOUT
matches typical test data
tON =VIN × [tON – (2.5 × 10-8)]
within 3%.
RON = VIN × 1.06 x f × Eff.
x 10-10
The t
corresponding to2.95
a particular
set of operating
RLIM =
conditions can be calculated based on empirical data from:
VOUT (V)
12.0
5.0
3.3
1.8
90
1
500
fLC = 87
1 500
CFF = 2 x π x √ L x COUT
2 × π × RFB1 x 5 x fLC
80
500
10µA
CSS = tSS ×
0.6V
RON (kΩ)
56.3
33.5
2.95 x 10-10
(IOCP + (0.5 × ∆IL))
+ 0.16kΩ
ILIM
RDS
Where:
■■ RLIM
■■ IOCP
■■ ΔIL
is resistor value in kΩ
for programming IOCP
VOUT
–1
RFB1 = RFB2 ×
0.6V
is the overcurrent value to be programmed
is the peak-to-peak inductor current ripple
■■ ILIM/RDS
= 2.4µA/mΩ is the minimum value of the
parameter specified in the tabulated
data
10µA
CSS = tSS ×
0.6V
■■ 0.16kΩ accounts for OCP comparator
offset
The above equation is for worst-case analysis and
safeguards against premature OCP. Typical value of IOCP,
for a given RLIM, will be higher than that predicted by
1
the above equation.
CFF =Graph of calculated IOCP vs. RLIM is
2
×
π
×
R
x 5 x fLC
FB1 9.
compared to typical IOCP in Figure
10µA
CSS = tSSin×Vterms
Now RON can Rbe calculated
OUT
0.6V–of1 operating conditions
FB1 = RFB2+×(0.50.6V
∆
IL))equation. At VIN = 24V,
×
VIN, VOUT, f and Eff.(Iusing
the
above
OCP
= = 6A and
f = 500kHz,RLIM
IOUT
using
the+ efficiency
numbers
0.16kΩ
ILIM
from Figure 22 we get the Rfollowing
R
:
ON
DS
1
CFF =
10µA5 x f
2
×
π
×
R
LC
Eff.
CSS(%)
= tSS × FB1f x(kHZ)
0.6V
VOUT
–1
RFB1 = R94
FB2 × 0.6V 700
XR79206
Overcurrent Protection (OCP)
If the load current exceeds the
VOUTprogrammed overcurrent
threshold IOCP for
tON =four consecutive switching cycles,
VIN ×hiccup
1.06 x f ×mode
Eff.
the module enters the
of operation.
In hiccup mode the MOSFET gates are turned off for 110ms
(hiccup timeout). Following the hiccup timeout a soft-start
is attempted. If OCPV persists, hiccup timeout will repeat.
OUT
-8
– [(2.5
× 10until
) × Vload
The module will remain
hiccup
mode
IN] current is
1.06 x f in
× Eff.
RON =the programmed IOCP
reduced below
.
In
order
to program
× 10-10) equation:
overcurrent protection use (2.95
the following
ON
VOUT
– [(2.5 × 10-8) × VIN]
1.06 x f × Eff. VOUT
RON = tON =
× 10
V (2.95
× 1.06
x f-10
×) Eff.
VIN IN
× [tON – (2.5 × 10-8)]
RON =
2.95 x 10-10
Where:
(IOCP + (0.5
× ∆IL))
■■ f
is the desired
frequency at
VOUT switching
-8
RLIM
=
–
[(2.5
×
10
) × VIN]
+
0.16kΩ
I
nominal
IOUT
LIM
1.06 x f × Eff.
R
R
=
DS
■■ Eff. is ON
the converter efficiency
to
(2.95VOUT
× 10-10corresponding
)
nominal IOUTtON = V × 1.06 x f × Eff.
IN
Substituting for tON in the first equation we get:
(I
+ (0.5VOUT
× ∆IL))
R
= ROCP
FB2 × 0.6V – 1+ 0.16kΩ
RLIMFB1
=
I
VOUT LIM
RDS – [(2.5 × 10-8) × VIN]
1.06 x f × Eff.
RON =
(2.95 × 10-10)
VIN × [tON – (2.5 × 10-8)]
Short-Circuit Protection (SCP)
If the output voltage drops below 60% of its programmed
value, the Module will enter hiccup
1 mode. Hiccup will persist
f =
until short-circuit LC
is removed. SCP circuit becomes active
2 x π x √ L x COUT
after PGOOD asserts high.
Over Temperature Protection (OTP)
OTP triggers at a nominal controller temperature of 150°C.
1
The gate of switching
RFF = FET and synchronous FET are
π
x
f x CFF
2
x
turned off. When controller temperature
cools down to
135°C, soft-start is initiated and operation resumes.
22.2
12.4
11
fLCR=FF = 2 x π x f x CFF
2 x π x √ L x COUT
1
CFF =
2 × π × RFB1 x 5 x fLC
RFF =
fLC =
1
2 x π x f x CFF
1
2 x π x √ L x COUT
REV1B
12/19
-8
VVIN × [tON – (2.5 × 10-8 )]
– [(2.5 × 10 -8) × VIN]
RON = OUT
1.06 VxIN
f ××Eff.
[t2.95
–x 10
(2.5-10× 10 )]
ONVOUT
RON =RON
tON
==
-10
(2.95
×
VIN ×2.95
1.06x 10
x10f-10
× )Eff.
CFF =
1
2 × π × RFB1 x 5 x fLC
XR79206
Applications Information
∆(Continued)
IL))
(IOCP + (0.5V×OUT
tON V=
OUT
V–OUT
-8
RLIMthe
= Output
VINILIM
×Voltage
1.06
x f ×× Eff.
+ 0.16kΩ
[(2.5
10
) × VIN]
Programming
t1.06
ON =x f × Eff.
R
VIN divider
×DS1.06 x as
f × Eff.
RON = voltage
Use an external
shown in Figure 27
(2.95 × 10-10)
to program the output voltage VOUT.
VOUT
– [(2.5 × 10-8) × VIN]
1.06
x
f
×
Eff.
V
V
∆IL))–×110-8) × V ]
+ (0.5 ×
RON R=FB1 =(IOCP
ROUT
–OUT
[(2.5
FB2 ×(2.950.6V
× 10-10) + 0.16kΩIN
RLIM =1.06 x f × Eff.
I
LIM
RON =
-10
R(2.95
DS × 10 )
Where RFB2 has a nominal value of 2kΩ.
(IOCP + (0.5 × ∆IL))
Programming
RLIMthe
= Soft-Start
IL)) + 0.16kΩ
(IOCP + I(0.5
10µA
LIM × ∆
= tRSS ×VOUT
Place a capacitor CCSS
between
the
SS and AGND pins to
SS
0.6V
R RFB1
= = RFB2 ×ILIM
DS
– 1+ 0.16kΩ
program the LIM
soft-start.
In order0.6V
to program
a soft-start time
RDS capacitance C
of t , calculate the required
from the
SS
following equation:
SS
VOUT
RFB1 = RFB2 ×
1 –1
CFF =
V0.6V
10µA
OUT
2
×
π
×
R
x–51x fLC
FB1
RFB1 =CRSS
=×
tSS ×0.6V
FB2
0.6V
Feed-Forward Resistor
(RFF) 1
fLC =
RFF, in conjunction with
similar to a
2 x π xC√FFL, x Cfunctions
OUT
high frequency pole and adds gain margin to the
frequency response. Calculate RFF from:
RFF =
1
2 x π x f x CFF
Where f is the switching frequency.
If RFF >0.02 x R1 then calculate RFF value from
RFF = 0.02 x R1.
Maximum Allowable Voltage Ripple at FB Pin
Note that the steady-state voltage ripple at feedback pin FB
(VFB,RIPPLE) must not exceed 50mV in order for the module
to function correctly. If VFB,RIPPLE is larger than 50mV then
COUT should be increased as necessary in order to keep
the VFB,RIPPLE below 50mV.
Feed-Forward Capacitor (CFF) 10µA
CSS = tSS
× 1is used to set the necessary
The feed-forwardfLC
capacitor
CFF
=
0.6V
110µA
phase margin when
using
CFFC=SS 2=xtSS
π
x×√ceramic
L x COUT output capacitors.
× π × RFB1
x 5 x fLC
0.6V
Calculate CFF from the 2following
equation:
1
CFF =
1 x5xf
RFF 2=× π × R1FB1
LC
1
fCLC
FF== 2 ×2πx ×π Rx f x CxFF5 x f
FB1
2 x π x √ L x COUT LC
Where fLC, the output filter double-pole frequency is
calculated from:
1
fLC =
1
fLC R= =2 x π x √1L x COUT
FF 2 x π x f x C
2 x π x √ L x CFF
OUT
You must use manufacturer’s DC derating curves to
1
determine the effective
capacitance
corresponding to VOUT.
RFF =
π
x
CFF
2
x
A load step test and/or a loop
response test
1f xfrequency
R =
should be performedFF
and 2if xnecessary
π x f x CFF CFF can be adjusted
in order to get a critically damped transient load response.
In certain conditions an alternate compensation scheme
may need to be employed using ripple injection from
the inductor. An application note is being developed to
provide more information about this compensation scheme.
REV1B
13/19
XR79206
Applications Information (Continued)
Typical Application Circuit
D1
MMSZ4685-TP
RZ
10k
VIN
3
2
1
0.1µF
CIN
0.1µF
VCC
CVCC
4.7µF
10µF
72
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
SS
PGOOD
FB
AGND
AGND
VIN
VCC
PGND
SW
SW
SW
SW
PGND
PGND
PGND
PGND
PGND
TON
ENMODE
AGND
AGND
ILIM
BST2
BST1
PVIN
PVIN
PVIN
PVIN
PVIN
PVIN
PVIN
PVIN
NC
PGND
PGND
PGND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
AGND
BST
PVIN
PGND
LX
VOUT
PGND
PGND
PGND
PGND
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
PGND
PGND
PGND
PGND
PGND
PGND
SW
SW
SW
SW
SW
SW
SW
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
RPGOOD
10k
VIN
10µF
RON
22.1k
CSS
47nF
FB
10µF
RLIM
3.48k
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
PGOOD
VIN
VIN = 24V Nominal
SW
R2
35.7k
1 - 2 = CCM
VCC
EN
C1
0.22µF
2 - 3 = DCM/CCM
J1
R1
30.1k
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
VOUT
500kHz, 3.3V, 6A
0.1µF
0.1µF
47µF
47µF
CFF
330pF
RFB1
9.09k
RFF
0.18k
FB
RFB2
2k
XR79206
Figure 27. Application Circuit
REV1B
14/19
XR79206
Package Description
BOTTOM VIEW
TOP VIEW
SIDE VIEW
DETAIL A
REV1B
15/19
XR79206
Package Description (Continued)
TERMINAL AND PAD EDGE DETAILS
REV1B
16/19
XR79206
Package Description (Continued)
RECOMMENDED STENCIL DESIGN
NOTE: Dashed line refers to solder stencil opening.
REV1B
17/19
XR79206
Package Description (Continued)
RECOMMENDED LAND PATTERN
NOTE: Dashed line refers to land pattern.
REV1B
18/19
XR79206
Ordering Information
Part Number
Operating
Temperature Range
Environmental
Rating
Package
Packaging
Quantity
Marking
XR79206EL-F
-40°C ≤ TJ ≤ 125°C
RoHS
10mm x 10mm x 4mm
QFN package
Tray
XR79206EL
YYWWF
XXXXXXXX
XR79206EVB
XR79206 evaluation board
NOTE:
YY = Year, WW = Work Week, F = Lead Free and Halogen Free, XXXXXXXX = Lot Number.
www.exar.com
48760 Kato Road
Fremont, CA 94538
USA
Tel.: +1 (510) 668-7000
Fax: +1 (510) 668-7001
Email: powertechsupport@exar.com
Exar Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. Exar Corporation conveys
no license under any patent or other right and makes no representation that the circuits are free of patent infringement. While the information in this publication has been
carefully checked, no responsibility, however, is assumed for inaccuracies.
Exar Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected
to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless Exar Corporation
receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of
Exar Corporation is adequately protected under the circumstances.
Reproduction, in part or whole, without the prior written consent of Exar Corporation is prohibited. Exar, XR and the XR logo are registered trademarks of Exar Corporation.
All other trademarks are the property of their respective owners.
©2016 Exar Corporation
XR79206_DS_030416
REV1B
19/19