AX3161

52KHz, 2A PWM Buck DC/DC Converter

 GENERAL DESCRIPTION

The AX3161 series are monolithic IC designed for a step-down DC/DC converter, and
own the ability of driving a 2A load without additional transistor. It saves board space. The
external shutdown function can be controlled by logic level and then come into standby
mode. The internal compensation makes feedback control having good line and load
regulation without external design. Regarding protected function, thermal shutdown is to
prevent over temperature operating from damage, and current limit is against over current
operating of the output switch. If current limit function occurs and VFB is down below 0.5V,
the switching frequency will be reduced. An external compensation is easily to system
stable; the low ESR output capacitor can be used.
The AX3161 series operates at a switching frequency of 52KHz thus allow smaller
sized filter components than what would be needed with lower frequency switching
regulators. The output version included fixed 5V, 12V, and an adjustable type. The chips
are available in standard TO263-5L, TO220-5L and TO220-5LR packages.

 FEATURES

- Output voltage: 5V and adjustable output version.

- Adjustable version output voltage range, 1.23V to 57V.
- 52KHz fixed switching frequency.
- Voltage mode non-synchronous PWM control.
- Thermal-shutdown and current-limit protection.
- ON/OFF shutdown control input.
- Short Circuit Protect (SCP).
- Operating voltage can be up to 60V.
- Output load current: 2A.
- TO263-5L, TO220-5L and TO220-5LR Pb-Free packages.
- Low power standby mode.
- Built-in switching transistor on chip.

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 AX3161

 BLOCK DIAGRAM
EN
200mV
V CC

220mV
CURRENT 1.235V 2.5V START
SOURCE REGULATOR UP
REFERENCE
BIAS

+
COMP.
_
Current
limit
52kHz _
COMP.
OSC.
FB +

R2
+
AMP + CONTROL 2A
_ COMP. + SWITCH
_ DRIVER
COMP.
R1
SW
Thermal
Shutdown Vss
ADJ : R2=0Ω , R1=OPEN

 PIN ASSIGNMENT
The packages of AX3161 are TO263-5L, TO220-5L and TO220-5LR the pin assignment is
given by:

TO263-5L ( Side View ) TO220-5L ( Side View )

5 EN 5 EN
Metal 4 FB Metal 4 FB
Tab 3 VSS Tab 3 VSS
GND 2 SW GND 2 SW
1 VCC
1 VCC
( Top View ) ( Top View )

TO220-5LR ( Side View )

Name Description
VCC Operating voltage input
SW Switching output
5 EN
Metal 4 FB VSS GND pin
Tab 3 VSS
GND 2 SW FB Output voltage feedback control
1 VCC
EN ON/OFF Shutdown
( Top View )

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 AX3161

 ORDER INFORMATION
Order Information
AX3161- XX XXX X

Output Voltage Package Type Packing

50: 5.0V M5: TO263-5L Blank : Tube
Blank:ADJ T5: TO220-5L A : Taping
T5R: TO220-5LR

Top Marking
ADJ FIX

Logo
AXY Y3 WW
1 61
X
Part number
ID code:internal
Logo
AX 3 1- 56 01 Part number
Output voltage
Y YWW X ID code:internal
WW:01~52
WW:01~52
Year: 10=2010 Year: 10=2010
11=2011 11=2011

 ABSOLUTE MAXIMUM RATINGS

Characteristics Symbol Rating Unit
Maximum Supply Voltage VCC +63 V
ON/OFF Pin Input Voltage VEN -0.3 to 35 V
Feedback Pin Voltage VFB -0.3 to 35 V
Output Voltage to Ground VOUT -0.8 V
Power Dissipation Internally limited PD ( TJ-TA ) / θJA W
Storage Temperature Range TST -65 to +150 °C
Operating Junction Temperature Range TJ -40 to +125 °C
Operating Supply Voltage VOP +4.5 to +60 V
TO263
Thermal Resistance from Junction to case θJC 3.5 °C/W
TO220
TO263
Thermal Resistance from Junction to ambient θJA 25 °C/W
TO220
Note 1: θJA is measured with the PCB copper area (need connect to VSS pins) of approximately 3 in2 (Multi-layer).

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 ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, TA=25°C, VCC=12V. ILOAD = 0.2A)
Characteristics Symbol Conditions Min Typ Max Units
Quiescent Current IQ V FB=1.5V for Adjustable
- 4 8 mA
version force driver off
Feedback bias current IFB V FB=1.3V
- -10 -50 nA
(Adjustable version only)
ISD EN pin=5V
Shutdown supply Current - 100 200 uA
VCC=60V
Oscillator frequency FOSC 40 52 65 KHz

Oscillator frequency of short (Adjustable) When VFB<0.5V - 15 - KHz

FSCP
circuit protect (Fixed)When < VOUT*40% - 15 - KHz
Max. Duty Cycle (ON) VFB=0V force driver on - 100 -
DC VFB=1.5V for Adjustable %
Min. Duty Cycle (OFF) - 0 -
version force driver off
Pear current, No outside circuit 2.3
Current limit ICL - - A
V FB=0V force driver on

Load Regulation( △ VOUT/VOUT ) △ VOUT IOUT = 0.2 to 2A - 0.6 1.2 %

VSA T IVOUT=0V
=2A, No outside circuit
Saturation voltage - 1.2 1.4 V
FB force driver on
SW Pin=0V No outside circuit - - -200 uA
SW pin leakage VFB=1.5V for Adjustable
ISW L
current version force driver off
SW Pin=-0.8V VCC=60V force driver off - -5 - mA

VIL Low (regulator ON) - 0.6

EN pin logic input threshold 1.3 V
voltage
VIH High (regulator OFF) 2.0 -

EN pin logic input current IH VEN=2.5V (OFF) - -0.1 -10 uA

EN pin input current IL VEN=0.5V (ON) - -0.01 -1 uA

Thermal shutdown Temp TSD - 150 - °C

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 ELECTRICAL CHARACTERISTICS (CONTINUED)

Version Characteristics Symbol Conditions Min Typ Max Units
Output Feedback ILOAD =0.2A VOUT
VFB 1.193 1.23 1.267 V
AX3161-ADJ voltage programmed for 3.3V
Efficiency η VCC = 12V, ILOAD=2A - 79 - %
Output voltage VOUT ILOAD =0.2A 4.85 5.00 5.15 V
AX3161-5.0V
Efficiency η VCC = 12V, ILOAD=2A - 83 - %

 APPLICATION CIRCUIT
(1) Fixed Output Voltage Versions

VIN=12V L1 Vout=5.0V/2A
1 2
U1 120uH
1
Vcc
2
SW 3 D1
Vss
C1 C2 4 B340A C3 C6
470uF 0.1uF FB 470uF 0.1uF
5
EN
AX3161-50

(2) Adjustable Output Voltage Version with Delayed Startup

VIN=12V L1 Vout=5V/2A
1 2
U1 120uH R1
1 4.7k C5
Vcc Option
2
SW 3 D1
C1 C2 4 Vss B340A C3 C6
470uF 0.1uF FB 470uF 0.1uF R2
5 1.5k
EN
R3 ON/OFF AX3161
100k

R1
VOUT = VFB  (1 + ), VFB = 1.23V, R2 = 0.47K ~ 3K
R2
Table 1 Resistor select for output voltage setting
VOUT R2 R1
3.3V 1.5K 2.5K
5V 1.5K 4.7K
12V 1.5K 13K

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L1 recommend value (IOUT=2A,)

VOUT 3.3V 5V 12V
VIN=12V 100uH 120uH NA
VIN=24V 120uH 150uH 200uH
VIN=32~48V 120uH 150uH 300uH

 FUNCTION DESCRIPTION
Pin Functions
VCC

This is the positive input supply for the IC switching regulator. A suitable input bypass
capacitor must be presented at this pin to minimize voltage transients and to supply the
switching currents needed by the regulator.

VSS
Circuit ground.

SW

Internal switch. The voltage at this pin switches between (+VCC – VSAT) and
approximately – 0.5V, with a duty cycle of approximately VOUT / VCC. To minimize coupling
to sensitive circuitry, the PC board copper area connected to this pin should be minimized.

Feedback

Senses the regulated output voltage to complete the feedback loop.

EN

Allows the switching regulator circuit to be shutdown using logic level signals thus
dropping the total input supply current to approximately 100uA. Pulling this pin below a
threshold voltage of approximately 1.3V turns the regulator on, and pulling this pin above
1.3V (up to a maximum of VCC) shuts the regulator down. If this shutdown feature is not
needed, the EN pin can be wired to the ground pin.

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Output Capacitor Selection

The output capacitor is required to filter the output and provide regulator loop stability.
The important capacitor parameters are; the 100 KHz Equivalent Series Resistance (ESR),
the RMS ripples current rating, voltage rating, and capacitance value. For the output
capacitor, the ESR value is the most important parameter. The ESR can be calculated from
the following formula.

V RIPPLE
  I L  ESR = 0.4A x 80mΩ= 32mV

An aluminum electrolytic capacitor's ESR value is related to the capacitance and its
voltage rating. In most case, higher voltage electrolytic capacitors have lower ESR values.
Most of the time, capacitors with much higher voltage ratings may be needed to provide the
low ESR values required for low output ripple voltage. It is recommended to replace this
low ESR capacitor by using a 470µF low ESR values < 80mΩ.

Thermal Considerations
The data for these curves was taken with the AX3161 operating as a buck-switching
regulator in an ambient temperature of 25°C (still air). These temperature increments are
all approximate and are affected by many factors. Higher ambient temperatures require
more heat sinker.
For the best thermal performance, wide copper traces and generous amounts of
printed circuit board copper (need connect to the VSS pins) should be used in the board
layout, (One exception is the SW(switch) pin, which should not have large areas of copper.)
Large areas of copper provide the best transfer of heat (lower thermal resistance) to the
surrounding air, and moving air lowers the thermal resistance even further.
Package thermal resistance and junction temperature increments are all approximate.
The increments are affected by a lot of factors. Some of these factors include board size,
shape, thickness, position, location, and even board temperature. Other factors are, trace
width, total printed circuit copper area, copper thickness, single or double-sided, multi-layer
board and the amount of solder on the board.
The effectiveness of the PC board to dissipate heat also depends on the size,
quantity and spacing of other components on the board, as well as whether the
surrounding air is still or moving. Furthermore, some of these components such as the
catch diode will add heat to the PC board and the heat can vary as the input voltage
changes. For the inductor, depending on the physical size, type of core material and the
DC resistance, it could either act as a heat sink taking heat away from the board, or it could
add heat to the board.

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PCB Layout Recommendations

GND
AX3161
TO263-5L

1 2 3 4 5 R2 R1
C1 C2
C5
VIN
GND
D1
C3 C6

VOUT
L1

1. Connect the C1 and C2 VIN bypass capacitor next to the VCC pin with a short return to the
VSS pin.
2. Keep the SW traces as short as is practically possible as these carry high peak currents to
decrease the EMI issue.
3. Carefully connect the noise sensitive signals such as FB as close to the IC as practically
possible.

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 TYPICAL CHARACTERISTICS
Efficiency (VOUT=3.3V) Efficiency (VOUT=5.0V)
Efficiency Test (VOUT=3.3V) Efficiency Test (VOUT=5V)
90 100
VIN=12V VIN=24V
80 90
70 80
VIN=5V 70 VIN=12V
60
Efficiency (%)

Efficiency (%)
60
50
50
40
40
30 30
20 20
10 10
0 0
0 0.5 1 1.5 2 0 0.5 1 1.5 2
IOUT (A) IOUT (A)

Power on test wave EN on test wave

(VIN=12V, VOUT=3.3V, IOUT=2A ) (VIN=12V, VOUT=5V, IOUT=2A )

Load Transient Response

(VIN=12V, VOUT=3.3V, IOUT=0.2~2A)

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 PACKAGE OUTLINES

(1) TO263-5L
E
10.9

L2

9.2
D

15.8
L

3.0
e b
1.0 1.71
Land Pattern Recommendation
(Unit: mm)

A
C2
C

L1

Dimensions in Millimeters Dimensions in Inches

Symbol
Min. Nom. Max. Min. Nom. Max.
A 4.06 4.45 4.83 0.16 0.175 0.19
b 0.51 0.76 0.99 0.02 0.03 0.039
C 0.38 0.56 0.74 0.015 0.022 0.029
C2 1.14 1.4 1.65 0.045 0.055 0.065
D 8.38 9.02 9.65 0.33 0.355 0.38
E 9,65 10.2 10.7 0.38 0.4 0.42
e 1.70 BSC 0.067 BSC
L 14.6 15.2 15.9 0.575 0.6 0.625
L1 1.78 2.29 2.79 0.07 0.09 0.11
L2 - - 1.68 - - 0.066
Mold flash shall not exceed 0.005inch per side
JEDEC outline: TO-263 BA

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 AX3161

(2) TO220-5L

E
θP A
F

Q
H1
D
L

b C
e J1
e1

Dimensions in Millimeters Dimensions in Inches

Symbol
Min. Nom. Max. Min. Nom. Max.
A 4.07 4.45 4.82 0.16 0.175 0.19
b 0.76 0.89 1.02 0.03 0.035 0.04
C 0.36 0.5 0.64 0.014 0.02 0.025
D 14.22 14.86 15.5 0.56 0.585 0.61
E 9.78 10.16 10.54 0.385 0.4 0.415
e 1.57 1.71 1.85 0.062 0.067 0.073
e1 6.68 6.81 6.93 0.263 0.268 0.273
F 1.14 1.3 1.45 0.045 0.051 0.057
H1 5.46 6.16 6.86 0.215 0.243 0.27
J1 2.29 2.74 3.18 0.09 0.108 0.125
L 13.21 13.97 14.73 0.52 0.55 0.58
θP 3.68 3.81 3.96 0.145 0.15 0.156
Q 2.54 2.73 2.92 0.1 0.107 0.115
Mold flash shall not exceed 0.005inch per side
JEDEC outline: NA

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(3) TO220-5LR

A
E
F
Q
H1

D
H2
d1

H3

d2

b J1
e
J2

J2
J1 A

Dimensions in Millimeters Dimensions in Inches

Symbol
Min. Nom. Max. Min. Nom. Max.
A 4.4 4.6 4.7 0.175 0.180 0.185
b 0.7 0.8 0.9 0.027 0.032 0.037
D 8.4 8.7 8.9 0.330 0.340 0.350
d1 1.0 0.039
d2 6.3 0.248
E 9.91 10.16 10.41 0.390 0.400 0.410
e 1.6 1.7 1.8 0.062 0.067 0.072
F 1.2 1.25 1.3 0.048 0.050 0.052
H1 6.4 0.250
H2 20.8 21.6 22.4 0.820 0.850 0.880
H3 23.9 24.7 25.5 0.942 0.972 1.002
J1 3.7 4.5 5.3 0.147 0.177 0.207
J2 8.4 0.331
Q 2.5 2.8 3.0 0.100 0.110 0.120

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