Liteon Semiconductor Corporation
LSP3131
PWM Control 3A Step-Down Converter
Rev1.0
1/7
PIN ASSIGNMENT
(Top View)
PIN DESCRIPTION
Pin Number Pin Name Pin Description
1 FB
Feedback Pin
2 EN
Enable Input Pin
H: Normal operation(Step-down operation)
L: Step-down operation stopped(All circuits deactivated)
3 OCSET Add an external resistor to set max output current
4 VCC IC power supply pin
5,6 OUTPUT Switch pin. Connect external inductor/diode here. Minimize trace area at this pin to
reduce EMI.
7,8 VSS GND pin
TYPICAL APPLICATION
Cellular Phones
PC Motherboard
LCD Monitor
Graphic Card
DVD-Video Player
Telecom Equipment
ADSL Modem
Printer and other Peripheral Equipment
Microprocessor core supply
Networking power supply
VCC
VSS
VSS
OUTPUT
OUTPUT
8
7
6
5
1
2
3
4
FB
EN
OCSET
GENERAL DESCRIPTION
LSP3131 consists of step-down switching regulator
with PWM control. These devices include a
reference voltage source, oscillation circuit, error
amplifier and internal PMOS.
LSP3131 provides low-ripple power, high efficiency,
and excellent transient characteristics. The PWM
control circuit is able to vary the duty ratio linearly
from 0 up to 100%. This converter also contains an
error amplifier circuit as well as a soft-start circuir
that prevents overshoot at startup. An enable
function, an over current protect function and a
short circuit protect function are built inside, and
when OCP or SCP happens, the operation
frequency will be reduced from 300KHz to 50KHz.
Also, an internal compensation block is built in to
minimum external component count.
With the addition of an internal P-channel Power
MOS, a coil, capacitors, and a diode connected
externally, these ICs can function as step-down
switching regulators. They serve as ideal power
supply units for portable devices when coupled with
the SOP8L mini-package, providing such
outstanding features as low current consumption.
Since this converter can accommodate an input
voltage up to 23V, it is also suitable for the operation
via an AC adapter.
FEATURES
Input voltage: 3.6V to 23V.
Output voltage: 0.8V to VCC.
Duty ratio: 0% to 100% PWM control
Oscillation frequency: 300KHz typ.
Soft-start, Current limit, Enable function
Thermal Shutdown function
Built-in internal SW P-channel MOSFET
SOP8L Package.
Liteon Semiconductor Corporation
LSP3131
PWM Control 3A Step-Down Converter
Rev1.0
2/7
ABSOLUTE MAXIMUM RATINGS(NOTE)
Parameter Value Unit
VCC Pin Voltage, VCC V
SS-0.3 to VSS+25 V
Feedback Pin Voltage, VFB VSS-0.3 to VCC V
EN Pin Voltage, VEN VSS-0.3 to VIN + 0.3 V
Switch Pin Voltage, VOUTPUT V
SS-0.3 to VIN + 0.3 V
Power Dissipation, PD Internally limited mW
Operating Temperature Range, TOPR -20 to +125 °C
Storage Temperature Range, TSTG -40 to +150 °C
Note: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions
for long periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TA= 25°C, unless otherwise specified.)
Parameter Symbol Test Conditions Min. Typ. Max. Unit
Input Voltage VIN 3.6 23 V
Feedback Voltage VFB IIOUT= 0.1A 0.784 0.8 0.816 V
Feedback Bias Current IFB IIOUT= 0.1A 0.1 0.5 µA
Switch Current ISW 3.5 A
Current Consumption During
Power Off ISSS VEN = 0 10 µA
Line Regulation ΔVOUT /VOUT VIN =5V~23V, IIOUT= 0.2A 1 2 %
Load Regulation ΔVOUT /VOUT IIOUT= 0.1A~3A 0.2 0.5 %
Oscillation Frequency fosc Measure waveform at SW pin 240 300 360 KHz
Frequency of Current Limit or
Short Circuit Protect fosc1 Measure waveform at SW pin 30 50 70 KHz
VSH Evaluate oscillation at SW pin 2.0
Enable Pin Input Voltage VSL Evaluate oscillation stop at
SW pin 0.8
V
ISH 20
Enable Pin Input Leakage
Current ISL -10 µA
OCSET Pin Bias Current IOCSET 75 90 105 µA
Soft-Start Time TSS 0.3 2 5 ms
VIN =5V, VFB = 0 80 90
Internal MOSFET Rdson Rdson VIN =12V, VFB = 0 50 65 mΩ
Efficiency EFFI VIN =12V, VOUT =5V,
IIOUT= 3A 91 %
Thermal Resistance
Junction to Ambient θJA 65 °C/W
Thermal Resistance
Junction to Case θJC 20 °C/W
Over temperature shutdown TSD 150 °C
Over temperature shutdown
Hysteresis THYS 25 °C
Liteon Semiconductor Corporation
LSP3131
PWM Control 3A Step-Down Converter
Rev1.0
3/7
FUNCTIONAL BLOCK DIAGRAM
FUNCTIONAL DESCROPTION
PWM Control
The LSP3131 consists of DC/DC converters that employ a pulse-width modulation (PWM) system. In converters of
the LSP3131, the pulse width varies in a range from 0 to 100%, according to the load current. The ripple voltage
produced by the switching can easily be removed through a filter because the switching frequency remains constant.
Therefore, these converters provide a low-ripple power over broad ranges of input voltage and load current.
Under Voltage Lockout
The under voltage lockout circuit of the LSP3131 assures that the high-side MOSFET driver outputs remain in the off
state whenever the supply voltage drops below 3.3V. Normal operation resumes once VCC rises above 3.5V.
RDS(ON) Current Limiting
The current limit threshold is setting by the external resistor connecting from VCC supply to OCSET. The internal
100uA sink current crossing the resistor sets the voltage at the pin of OCSET. When the PWM voltage is less than
the voltage at OCSET, an over-current condition is triggered.
I PEAK ×R DS(ON) =I OCSET × R OCSET
See above formula for setting the current limit value
Liteon Semiconductor Corporation
LSP3131
PWM Control 3A Step-Down Converter
Rev1.0
4/7
TYPICAL APPLICATION CIRCUIT
Note1:CIN/COUT can be Electro capacitor or Tan capacitor; The typical CIN Electro capacitor is 470uF/35V,the typical
CIN Tan capacitor is 100uF/35V; The typical COUT Electro capacitor is 470uF/16V,the typical COUT Tan capacitor is
22uF/16V;
Note2: VOUT=VFB*(1+RA/RB)
RB=0.7KΩ~5KΩ VIN=12V, IMAX=3A
VOUT 2.5V 3.3V 5V
L1 Value 15uH 18uH 22uH
TEST CIRCUITS
1) Enable Function Test 2) Feedback Function Test
3) Operation Function Test
Liteon Semiconductor Corporation
LSP3131
PWM Control 3A Step-Down Converter
Rev1.0
5/7
TYPICAL CHARACTERISTICS
Liteon Semiconductor Corporation
LSP3131
PWM Control 3A Step-Down Converter
Rev1.0
6/7
TYPICAL CHARACTERISTICS (CONTINUED)
ORDERING INFORMATION
MARKING INFORMATION
Liteon Semiconductor Corporation
LSP3131
PWM Control 3A Step-Down Converter
Rev1.0
7/7
PACKAGE INFORMATION
Dimensions In Millimeters Dimensions In Inches
Symbol Min. Nom. Max. Min. Nom. Max.
A 1.40 1.60 1.75 0.055 0.063 0.069
A1 0.10 0.25 0..004 0.010
A2 1.30 1.45 1.50 0.051 0.057 0.059
B 0.33 0.41 0.51 0.013 0.016 0.020
C 0.19 0.20 0.25 0.0075 0.008 0.010
D 4.80 5.05 5.30 0.189 0.199 0.209
E 3.70 3.90 4.10 0.146 0.154 0.161
e 1.27TYP. 0.050TYP.
H 5.80 5.99 6.20 0.228 0.236 0.244
L 0.38 0.71 1.27 0.015 0.028 0.050
θ 0
ο 8
ο 0ο 8
ο
E
H
L
θ
VIEW “A”
e
B
D
A2
A
A1
7
ο
(4х)
0.015 х45
ο
C
VIEW “A”
7
ο
(4х)
