AX5511
1.2MHz, High Voltage, Boost Converter
 GENERAL DESCRIPTION
The AX5511 is a current mode step up converter intended for small, low power
applications. The converter input voltage ranging from 2.6V to 5.5V. The Output voltage can
be set up to 27V. The frequency is 1.2MHz allows the use of small external inductors and
capacitors and provides fast transient response. Internal soft start results in small inrush
current and extends battery life. Internal power MOSFET with very low RDS (ON) provides
high efficiency. The AX5511 automatically transits from PWM to PFM during light load
condition further increasing efficiency. The converter also provides protection functions such
as under-voltage lockout, current limit and thermal shutdown. The AX5511 is available in
5-pin TSOT-23 package.
 FEATURES
-
2.6V to 5.5 V operating input voltage range
Adjustable output voltage range up to 27V
1.2MHz Fixed Switching Frequency
Internal soft-start function
Current limit and Thermal shutdown protection
Under voltage Lockout
≤ 1µA Shutdown Current
Available in the 5-pin TSOT-23 Package
 BLOCK DIAGRAM
EN
VCC
UVLO
Soft
Start
Enable/
Disable
Thermal
Shutdown
Summing
Comparator
Vref
1.238V
FB
Error
Amplifier
SW
Control and
Driver Logic
N-MOS
Oscillator
1.2MHz
Slope
Compensation
Current
Sense
GND
1/9
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Rev.1.2 Oct.27, 2011
AX5511
 PIN ASSIGNMENT
The package of AX5511 is TSOT-23-5L; the pin assignment is given by:
Name
Description
Input Supply Pin.
VCC
Must be locally bypassed.
Regulator On/Off Control Input.
A high input at EN turns on the
converter, and a low input turns it
(Top View)
EN off.
When not used, connect EN to the
input source for automatic startup.
5 VCC
SW 1
The EN pin cannot be left floating.
GND 2
Feedback Input.
FB
FB voltage is 1.238V.
4 EN
FB 3
Connect a resistor divider to FB.
GND Ground.
Power Switch Output.
TSOT-23-5L
SW is the drain of the internal
MOSFET switch.
SW Connect the power inductor and
output rectifier to SW.
SW can swing between GND and
27V.
 ORDER/MARKING INFORMATION
Order Information
AX5511 XX X
Package Type
Packing
BT: TSOT-23-5L Blank : Tube
A: Taping
Top Marking
BA Y WX
AX5511
ID code: internal
WW: 01~26(A~Z)
27~52(a~z)
Year: A=2010
1=2011
 ABSOLUTE MAXIMUM RATINGS (at TA=25°C)
Characteristics
Symbol
Rating
Unit
VCC Pin Voltage
VCC
GND - 0.3 to GND + 6.5
V
EN,FB Pin Voltage
GND - 0.3 to VCC + 0.3
V
SW Pin Voltage
VSW
30
V
Power Dissipation
PD
( TJ-TA ) / θJA
mW
Storage Temperature Range
TST
-40 to +150
°C
Operating Junction Temperature Range
TOP
-40 to +125
°C
110
Thermal Resistance from Junction to case
θJC
°C/W
250
Thermal Resistance from Junction to ambient
θJA
°C/W
Note: θJA is measured with the PCB copper area of approximately 1 in2(Multi-layer).
2/9
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Rev.1.2 Oct.27, 2011
AX5511
 ELECTRICAL CHARACTERISTICS
(VCC = 5V, VOUT=12V, TA = 25°C, unless otherwise noted)
Characteristics
Symbol
Conditions
Input Voltage range
VCC
Under Voltage Lockout
UVLO
Rising
UVLO Hysteresis
Min
Typ
2.6
-
Max Units
5.5
V
-
2.35 2.60
V
-
-130
-
mV
3
-
27
V
Step-Up Voltage Adjust Range
VOUT
Operating quiescent current
ICCQ
IOUT= 0mA, VFB =1.5V
-
150
250
μA
Shutdown current
ISD
VEN=0V
-
0.1
1
μA
Feedback Voltage
VFB
FB Input Leakage Current
Line Regulation
Load Regulation
Switching frequency
Maximum Duty
N-channel MOSFET
current limit
MOSFET on-resistance
(Note 1)
IFB-LKG VFB = 1.3V
VIN = 2.5 to 5.5V
IOUT = 20mA
VIN = 5V
IOUT = 1mA to 400mA
FOSC
DMAX
ILIM
RDS(on)
1.213 1.238 1.263
V
-100 0.01 +100
nA
-
0.2
-
%
-
0.2
-
%
900 1200 1500 KHz
82
87
-
%
Duty=50%
-
1.9
-
A
VCC=3V, ISW=1A
-
650
-
VCC=5V, ISW=1A
-
500
-
VSW = 27V, VFB =1.5V
-
-
1
µA
mΩ
SW Leakage Current
ISWL
EN high-level input voltage
VIH
1.0
-
-
V
EN low-level input voltage
VIL
-
-
0.4
V
EN Hysteresis
hys
-
200
-
mV
-
0.01
0.1
μA
EN input leakage current
IEN-LKG VEN=GND or VCC
Thermal Shutdown
TDS
-
150
-
Thermal Shutdown Hysteresis
TSH
-
35
-
°C
Note1: Guaranteed by design.
3/9
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Rev.1.2 Oct.27, 2011
AX5511
 APPLICATION CIRCUIT
VIN=5V
R4
1M
ON
C1
10uF
D1
B240A
L1
4.7uH
AX5511
U1
5 VCC
4
EN
SW
FB
C3
R2
470K
1
3
GND
2
OFF
VOUT=12V
C2
R3
R1
54K
4.7uF
1nF
R2
VOUT = 1.238V X (1 + ------- )
R1
R2 Suggest 390K~820K
VIN
2.6~3.6V
2.6~5.3V
2.6~5.5V
VOUT
5V
7V
7.5~27V
R3
120KΩ
82KΩ
0Ω
 APPLICATION INFORMATION
Setting the Output Voltage
Application circuit item shows the basic application circuit with AX5511 adjustable
output version. The external resistor sets the output voltage according to the following
equation:
R2
VOUT = 1.238V × (1+
)
R1
For most applications, R2 is a suggested a value by 390K~820KΩ. Place the
resistor-divider as close to the IC as possible to reduce the noise sensitivity.
Under Voltage Lockout (UVLO)
To avoid mis-operation of the device at low input voltages an under voltage lockout is
included that disables the device, if the input voltage falls below (2.35V-130mV).
4/9
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AX5511
Input Capacitor Selection
The input capacitor reduces the surge current drawn from the input and switching
noise from the device. The input capacitor impedance at the switching frequency shall be
less than input source impedance to prevent high frequency switching current passing to the
input. A low ESR input capacitor sized for maximum RMS current must be used. Ceramic
capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR
and small temperature coefficients. A 10µF ceramic capacitor for most applications is
sufficient. For a lower output power requirement application, this value can be decreased.
Output Capacitor Selection
The output capacitor is required to keep the output voltage ripple small and to ensure
regulation loop stability. The output capacitor must have low impedance at the switching
frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their
low ESR and high ripple current. A 4.7uF ceramic capacitors works for most of the
applications. Higher capacitor values can be used to improve the load transient response.
Layout Guide
VCC
C1's ground must be as
closer to IC's GND pin as
possible
R4
EN
5
4
C3
AX5511
R1
C1
VIN
L1
1
2
3
SW
GND
FB
SW should be connected to Inductor by
wide and short trace, keep sensitive
components away from this trace
C2's ground must be as
closer to IC's GND pin as
possible
R3
R2
C2
VOUT
D1
5/9
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Rev.1.2 Oct.27, 2011
AX5511
 TYPICAL CHARACTERISTICS
VIN V.S Frequency
VIN V.S ICCQ
2
250
1.8
1.6
Frequency (MHz)
300
ICCQ (uA)
200
150
100
1.4
1.2
1
0.8
0.6
0.4
0.2
50
VFB=1.5V
0
0
2.5
3
3.5
4
4.5
5
2.5
5.5
3
3.5
4
4.5
5
5.5
VIN (V)
VIN (V)
VIN V.S Feedback Voltage
IOUT V.S Feedback Voltage
1.28
1.27
1.27
1.26
1.25
1.25
VFB (V)
VFB (V)
1.26
1.24
1.23
VIN=5V
1.24
VIN=3.3V
1.23
1.22
1.22
1.21
VOUT=12V
1.2
1.21
2.5
3
3.5
4
4.5
5
5.5
0
50 100 150 200 250 300 350 400 450
VIN (V)
IOUT (mA)
Temperature V.S Frequency
Temperature V.S Feedback Voltage
1.28
2
1.27
1.8
1.6
Frequency (MHz)
VFB (V)
1.26
1.25
1.24
1.23
1.22
1.4
1.2
1
0.8
0.6
0.4
VIN=5V, VOUT=12V
IOUT=10mA
1.21
1.2
0.2
VIN=5V
0
-40℃ -20℃
0℃
25℃
50℃
Temperature
75℃ 100℃ 125℃
-40℃ -20℃
0℃
25℃
50℃
75℃ 100℃ 125℃
Temperature
6/9
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Rev.1.2 Oct.27, 2011
AX5511
 TYPICAL CHARACTERISTICS (CONTINUOUS)
Temperature V.S Maximum Duty
90
1.8
89
1.6
88
Maximum Duty (%)
EN Threshold Voltage (V)
Temperature V.S EN Threshold Voltage
2
1.4
1.2
ENH
1
0.8
0.6
ENL
0.4
0.2
87
86
85
84
83
82
81
VIN=5V
VIN=5V
80
0
-40℃ -20℃
0℃
25℃
50℃
-40℃ -20℃
75℃ 100℃ 125℃
0℃
25℃
75℃ 100℃ 125℃
Duty V.S Current Limit
Temperature V.S UVLO
3
3
2.8
2.5
VIN=5V
2.6
2
Rising
Current Limit (A)
UVLO (V)
50℃
Temperature
Temperature
2.4
2.2
2
Falling
VIN=3.3V
1.5
1
0.5
1.8
0
1.6
-40℃ -20℃
0℃
25℃
50℃
30%
75℃ 100℃ 125℃
40%
50%
70%
Efficiency Test
Efficiency Test
100
100
90
90
80
70
80
Efficiency (%)
Efficiency (%)
60%
Duty
Temperature
60
50
40
VIN=5V
VIN=3.3V
70
60
50
40
30
30
20
20
VIN=3.3V
VOUT=5V
10
10
VOUT=12V
0
0
0
100
200
300
400
IOUT (mA)
500
600
700
0
100
200
300
400
500
IOUT (mA)
7/9
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Rev.1.2 Oct.27, 2011
AX5511
 TYPICAL CHARACTERISTICS (CONTINUOUS)
Load Transient
Load Transient
Power ON
Enable ON
Power ON
Enable ON
8/9
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AX5511
 PACKAGE OUTLINES
θ
D
L
E1
E
L1
R
b
e
y
A1
A
A2
e1
C
L2
Dimensions in Millimeters
Min.
Nom.
Max.
A
1.1
A1
0
0.1
A2
0.7
0.9
1
b
0.3
0.4
0.5
C
0.08
0.14
0.2
D
2.8
2.9
3
E
2.6
2.8
3
E1
1.5
1.6
1.7
e
0.95 BSC.
e1
1.90 BSC.
L
0.3
0.45
0.6
L1
0.60 REF.
L2
0.25 BSC.
y
0.1
R
0.1
o
θ
0
8o
JECED outline: MO-193 AB
Symbol
Dimensions in Inches
Min.
Nom.
Max.
0.043
0
0.004
0.028
0.035
0.039
0.012
0.016
0.02
0.003
0.006
0.008
0.11
0.114
0.118
0.102
0.11
0.118
0.059
0.063
0.067
0.037 BSC.
0.075 BSC.
0.012
0.018
0.024
0.024 REF.
0.010 BSC.
0.004
0.004
o
0
8o
9/9
Axelite Confidential Materials, do not copy or distribute without written consent.
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