Liteon Semiconductor Corporation
LSP3133
PWM Control 2A Step-Down Converter
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.
GENERAL DESCRIPTION
LSP3133 consists of step-down switching regulator
with PWM control. These devices include a
reference voltage source, oscillation circuit, error
amplifier and internal PMOS.
LSP3133 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 circuit
that prevents overshooting 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.
TYPICAL APPLICATION
PC Motherboard
LCD Monitor
Graphic Card
DVD-Video Player
Telecom Equipment
ADSL Modem
Printer and other Peripheral Equipment
Microprocessor core supply
Networking power supply
PIN ASSIGNMENT
(Top View)
FB 1
EN 2
OCSET 3
VCC 4
8 VSS
7 VSS
6
OUTPUT
5 OUTPUT
PIN DESCRIPTION
Pin Number Pin Name
1
2
3
4
5,6
7,8
FB
EN
OCSET
VCC
OUTPUT
VSS
Feedback Pin
Enable Input Pin
H: Normal operation(Step-down operation)
L: Step-down operation stopped(All circuits deactivated)
Add an external resistor to set max output current
IC power supply pin
Switch pin. Connect external inductor/diode here. Minimize trace area at this pin to
reduce EMI.
GND pin
Pin Description
1/7
Rev1.0
Liteon Semiconductor Corporation
LSP3133
PWM Control 2A Step-Down Converter
ABSOLUTE MAXIMUM RATINGS(NOTE)
Parameter
VCC Pin Voltage, V
CC
Feedback Pin Voltage, V
FB
EN Pin Voltage, V
EN
Switch Pin Voltage, V
OUTPUT
Power Dissipation, P
D
Operating Temperature Range, T
OPR
Storage Temperature Range, T
STG
Value
V
SS
-0.3 to V
SS
+25
V
SS
-0.3 to V
CC
V
SS
-0.3 to V
IN
+ 0.3
V
SS
-0.3 to V
IN
+ 0.3
Internally limited
-20 to +125
-40 to +150
Unit
V
V
V
V
mW
°C
°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
(V
IN
= 12V, T
A
= 25°C, unless otherwise specified.)
Parameter
Symbol
Input Voltage
Feedback Voltage
Feedback Bias Current
Switch Current
Current Consumption During
Power Off
Line Regulation
Load Regulation
Oscillation Frequency
Frequency of Current Limit or
Short Circuit Protect
Enable Pin Input Voltage
Enable Pin Input Leakage
Current
OCSET Pin Bias Current
Soft-Start Time
Internal MOSFET Rdson
Efficiency
Thermal Resistance
Junction to Ambient
Thermal Resistance
Junction to Case
Over temperature shutdown
Over temperature shutdown
Hysteresis
V
IN
V
FB
I
FB
I
SW
I
SSS
I
IOUT
= 0.1A
I
IOUT
= 0.1A
V
EN
= 0
Test Conditions
Min.
3.6
0.784
2.5
10
1
0.2
300
50
2
0.5
360
70
0.8
0.1
Typ.
Max.
23
0.816
0.5
Unit
V
V
µA
A
µA
%
%
KHz
KHz
V
µA
105
2
150
100
µA
ms
mΩ
%
°C/W
°C/W
°C
°C
V
IN
=5V~23V
ΔV
OUT
/V
OUT
I
IOUT
= 0.1A~2A
ΔV
OUT
/V
OUT
Measure waveform at SW pin
fosc
fosc1
V
SH
V
SL
I
SH
I
SL
I
OCSET
T
SS
R
dson
EFFI
θ
JA
θ
JC
T
SD
T
HYS
V
IN
=5V, V
FB
= 0
V
IN
=12V, V
FB
= 0
V
IN
=12V, V
OUT
=5V,
I
IOUT
= 2A
Measure waveform at SW pin
Evaluate oscillation at SW pin
Evaluate oscillation stop at
SW pin
240
30
2.0
0.8
20
-10
90
1
110
70
92
150
60
150
25
75
0.3
2/7
Rev1.0
Liteon Semiconductor Corporation
LSP3133
PWM Control 2A Step-Down Converter
FUNCTIONAL BLOCK DIAGRAM
FUNCTIONAL DESCROPTION
PWM Control
The LSP3133 consists of DC/DC converters that employ a pulse-width modulation (PWM) system. In converters of
the LSP3133, 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 LSP3133 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.
R
DS(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
3/7
Rev1.0
Liteon Semiconductor Corporation
LSP3133
PWM Control 2A Step-Down Converter
TYPICAL APPLICATION CIRCUIT
Note1:C
IN/
C
OUT
can be Electro capacitor or Tan capacitor; The typical C
IN
Electro capacitor is 470uF/35V,the typical
C
IN
Tan capacitor is 100uF/35V; The typical C
OUT
Electro capacitor is 470uF/16V,the typical C
OUT
Tan capacitor is
22uF/16V;
Note2: V
OUT
=V
FB
*(1+R
A
/R
B
)
R
B
=0.7KΩ~5KΩ
V
IN
=12V, I
MAX
=2A
V
OUT
L1 Value
2.5V
22uH
3.3V
27uH
5V
33uH
TEST CIRCUITS
1) Enable Function Test
2) Feedback Function Test
3) Operation Function Test
4/7
Rev1.0
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