Liteon Semiconductor Corporation
LSP3125A
150KHZ 2A PWM Buck DC/DC Converter
FEATURES
Output voltage: 3.3V, 5V, 12V and adjustable
output version
Adjustable version output voltage range, 1.23V
to 37V ± 4%
150KHz ±15% fixed switching frequency
Voltage mode non-synchronous PWM control
Thermal-shutdown and current-limit protection
ON/OFF shutdown control input
Operating voltage can be up to 40V
Output load current: 2A
SOP8L packages
Low power standby mode
Built-in switching transistor on chip
GENERAL DESCRIPTION
T
he LSP3125A series are monolithic IC designed for
TYPICAL APPLICATION
Simple High-efficiency step-down regulator
On-card switching regulators
Positive to negative converter
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 FB is down below 0.5V, the
switching frequency will be reduced. The LSP3125A
series operates at a switching frequency of 150KHz
thus allow smaller sized filter components than what
would be needed with lower frequency switching
regulators. Other features include a guaranteed ± 4%
tolerance on output voltage under specified input
voltage and output load conditions, and ± 15% on the
oscillator frequency. The output version included fixed
3.3V, 5V, 12V, and an adjustable type. The chips are
available in a standard SOP8L package.
PIN ASSIGNMENT
(Top View)
PIN DESCRIPTION
Name
VIN
OUTPUT
FB
SD
GND
GND
GND
GND
No.
1
2
3
4
5
6
7
8
Description
Operating Voltage Input
Switching Output
Output Voltage Feedback Control
On/Off Shutdown
Ground
Ground
Ground
Ground
1/9
Rev1.4
Liteon Semiconductor Corporation
LSP3125A
150KHZ 2A PWM Buck DC/DC Converter
ABSOLUTE MAXIMUM RATINGS
Parameter
Supply Voltage
On/Off Pin Input Voltage
Feedback Pin Voltage
Output Voltage to Ground
Power Dissipation
Storage Temperature
Operating Temperature
Operating Voltage
Value
+45
-0.3 to +25
-0.3 to +25
-1
Internally Limited
-65 to +150
-40 to +125
+4.5 to +40
Unit
V
V
V
V
W
℃
℃
V
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, V
IN
=12V for 3.3V, 5V and adjustable version and V
IN
=18V for the 12V version. I
LOAD
=
0.5A)
Parameter
Feedback Bias Current
Oscillator Frequency
Short Circuit Oscillator
Frequency
Saturation Voltage
Maximum Duty Cycle(On)
Minimum Duty Cycle(Off)
Current Limit
Output
Leakage
Current
Output=-1
Quiescent Current
Output=0
Standby Quiescent Current
ON/OFF Pin Logic Input
Threshold Voltage
ON/OFF Pin Input Current
ON/OFF Pin Logic Input
Current
Thermal Resistance
Thermal Resistance with
Copper Area of Approximately
3 in
2
Symbol
I
FB
F
osc
F
CSP
V
SAT
DC
When Current Limit Occur and
V
FB
＜
0.5V, T
A
=25°C
I
OUT
= 2A, No Outside Circuit ,
V
FB
= 0V force drive on
V
FB
= 0V force drive on
V
FB
=12V force drive off
Peak Current
No Outside Circuit ,
V
FB
= 0V force drive on
No Outside Circuit ,
V
FB
= 12V force drive off
V
IN
= 40V
V
FB
= 12V force drive off
ON/OFF Pin=5V,V
IN
= 40V
Low (Regulator ON)
High (Regulator OFF)
V
LOGIC
=0.5V(ON)
V
LOGIC
=2.5V(OFF)
SOP8L
SOP8L
Junction to Case
Junction to
Ambient
15
70
℃/W
2.0
Test Conditions
V
FB
= 1.3V
(Adjustable Version Only)
Min.
Typ.
-10
127
110
10
150
30
1.25
0
3.6
3.4
6.9
7.5
-50
5
70
1.3
-30
10
200
250
0.6
-5
-15
µA
µA
mA
mA
µA
V
Max.
-50
-100
173
173
50
1.4
1.5
100
Unit
nA
kHz
kHz
V
%
A
I
CL
I
L
I
Q
I
STBY
V
IL
V
IH
I
L
I
H
θ
JC
θ
JA
2/9
Rev1.4
Liteon Semiconductor Corporation
LSP3125A
150KHZ 2A PWM Buck DC/DC Converter
ELECTRICAL CHARACTERISTICS(CONTINUED)
(Unless otherwise specified, V
IN
=12V for 3.3V, 5V and adjustable version and V
IN
=18V for the 12V version. I
LOAD
=
0.5A)
Parameter
Output
Feedback
Efficiency
Output
Feedback
Efficiency
Output
Feedback
Efficiency
Output
Feedback
LSP3125A-3.3
V
LSP3125A-5.0
V
LSP3125A-12
V
LSP3125A-AD
J
Symbol
V
FB
η
V
OUT
η
V
OUT
η
V
OUT
Test Conditions
4.5V
≤V
IN
≤40V
0.2A
≤I
LOAD
≤2A
V
OUT
Programmed for 3V
V
IN
=12V, I
LOAD
= 2A
4.5V
≤V
IN
≤40V
0.2A
≤I
LOAD
≤2A
V
IN
=12V, I
LOAD
= 2A
7V
≤V
IN
≤40V
0.2A
≤I
LOAD
≤2A
V
IN
=12V, I
LOAD
= 2A
15V
≤V
IN
≤40V
0.2A
≤I
LOAD
≤2A
Min.
1.193
1.18
75
3.168
3.135
78
4.8
4.75
83
11.52
5
5.2
5.25
12.48
3.3
3.432
3.465
Typ.
1.23
Max.
1.267
1.28
Unit
V
%
V
%
V
%
V
12
11.4
12.6
Efficiency
η
V
IN
=15V, I
LOAD
= 2A
90
Specifications with boldface are for full operating temperature range, the other type are for T
J
=25°C
%
FUNCTIONAL BLOCK DIAGRAM
3/9
Rev1.4
Liteon Semiconductor Corporation
LSP3125A
150KHZ 2A PWM Buck DC/DC Converter
FUNCTION DESCRIPTION
Pin Description
+VIN
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.
Ground
Circuit Ground
Output
Internal Switch. The voltage at this pin switches between (+V
IN
-V
SAT
) and approximately -0.5V, with a duty cycle of
approximately V
OUT
/V
IN
. To minimize coupling to sensitive circuitry, the PC board copper area connected to this pin
should be minimized.
Feedback
Sense the regulated output voltage to complete the feedback loop.
SD
Allows the switching regulator circuit to be shutdown using logic level signals thus dropping the total input supply
current to approximately 150uA. 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 18V) shuts the regulator down. If this shutdown feature is
not needed, the SD pin can be wired to the ground pin.
Thermal Considerations
T
he SOP8L package needs a heat sink under most conditions. The size of the heatsink depends on the input
voltage, the output voltage, the load current and the ambient temperature. The LSP3125A junction temperature
rises above ambient temperature for a 2A load and different input and output voltages. The data for these curves
was taken with the LSP3125A(SOP8L package) operating as a buck-switching regulator in an ambient temperature
25℃ (still air). These temperature increments are all approximate and are affected by many factors. Higher ambient
temperatures requires more heat sinker.
For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper should
be used in the board layout. (One exception is the output (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.
4/9
Rev1.4
Liteon Semiconductor Corporation
LSP3125A
150KHZ 2A PWM Buck DC/DC Converter
TYPICAL APPLICATION CIRCUIT
(1) Fixed Output Version Circuit
(2) Adjustable Version Circuit
Vout=V
FB
*(1+R1/R2); V
FB
=1.23V; R2=1K typical
Remark:
For input-output voltages greater than approximately 35V(ex:Vin=40V,Vout<=5V), the additional capacitor
CFF 10nF is recommended between FB and Vout. The capacitor type can be ceramic, plastic, etc.
5/9
Rev1.4
PCB设计
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