LSP7502
20V/3A High Power LED Driver
GENERAL DESCRIPTION
LSP7502 consists of step-down switching
regulator with PWM control. The device is suitable for
the high power LED driver with traditional DC/DC
buck solution. The device includes a reference
voltage source, oscillation circuit, error amplifier,
internal PMOS and etc.
LSP7502 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 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 600KHz to 60KHz. 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
20V, it is also suitable for the operation via an AC
adapter.
The feedback voltage is as low as 200mV that
much reduces power loss and improves efficiency.
FEATURES
Input voltage: 3.6V to 20V.
0.2V Low feedback Voltage
Duty ratio: 0% to 100% PWM control
Oscillation frequency: 500KHz typ.
Soft-start, Current limit, Enable function
Thermal Shutdown function
Built-in internal SW P-channel MOSFET
Exposed paddle SOP8L Package.
TYPICAL APPLICATIONS
High Power LED driver
Backlight system
Lighting power
PIN ASSIGNMENT
FB 1
EN 2
OCSET 3
VCC 4
8 VSS
7 VSS
6
OUTPUT
5 OUTPUT
PIN DESCRIPTION
Pin Number
1
2
3
4
5,6
7,8
Pin Name
FB
EN
OCSET
VCC
OUTPUT
VSS
Pin Description
Feedback Pin, Connect a resistor between FB to GND and determine the I
LED
Power-off 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
LSP7502 Preliminary
2009/7/31
Liteon Semiconductor Corp.
*This is Preliminary Version. All the parameters may change.
1/1
LSP7502
20V/3A High Power LED Driver
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
+23
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
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
Over temperature shutdown
Over temperature shutdown
Hysteresis
Symbol
V
IN
V
FB
I
FB
I
SW
I
SSS
ΔV
OUT
/V
OUT
ΔV
OUT
/V
OUT
fosc
fosc1
V
SH
V
SL
I
SH
I
SL
I
OCSET
T
SS
R
dson
T
SD
T
HYS
V
IN
=5V, V
FB
= 0V
V
IN
=12V, V
FB
= 0V
75
0.3
V
EN
= 0
V
IN
=5V~20V
I
IOUT
= 0.1A~2A
Measure waveform at SW pin
Measure waveform at SW pin
Evaluate oscillation at SW pin
Evaluate oscillation stop at SW pin
2.0
0.8
20
-10
90
2
80
50
150
25
105
5
90
70
400
I
IOUT
= 0.1A
I
IOUT
= 0.1A
3.5
10
1
0.2
500
100
2
0.5
600
Test Conditions
Min.
3.6
0.192
0.2
0.1
Typ.
Max.
20
0.208
0.5
Unit
V
V
µA
A
µA
%
%
KHz
KHz
V
µA
µA
ms
mΩ
°C
°C
LSP7502 Preliminary
2009/7/31
Liteon Semiconductor Corp.
*This is Preliminary Version. All the parameters may change.
2/2
LSP7502
20V/3A High Power LED Driver
THERMAL IMPEDIENCE
Thermal Resistance
Junction to Ambient
Thermal Resistance
Junction to Case
θ
JA
θ
JC
80
20
°C/W
°C/W
FUNCTIONAL BLOCK DIAGRAM
Figure 1. Function Block Diagram
FUNCTIONAL DESCRIPTION
PWM Control
The LSP7502 consists of DC/DC converters that employ a pulse-width modulation (PWM) system. In
converters of the LSP7502, 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 LSP7502 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
LSP7502 Preliminary
2009/7/31
Liteon Semiconductor Corp.
*This is Preliminary Version. All the parameters may change.
3/3
LSP7502
20V/3A High Power LED Driver
The formula above can set the current limit value.
I
LED
calculating
Connect a resistor between FB to GND and determine the I
LED
, I
LED
=V
FB
/R
FB
=200/R
FB
(mΩ)
The power dissipation of the R
FB
: Pd=I
LED
*V
FB
Dimming
The LSP7502 could adjust the LED light intensity through dimming function. There are 2 ways of dimming
function.
One is the analog dimming. The analog dimming function could be accomplished by using a DC voltage to
control the feedback voltage, as shown in Figure 2. As the DC voltage increases, current starts flowing down R1,
R2 and R3. The loop will continue to regulate the feedback voltage to 200mV. Thus the current through LED
would be decreased by the same amount of current as is being injected from the DC voltage source. With a
V
DC
from 0.2V to 5.0V, the resistor values shown for R2 and R3 can control the LED current from I
LEDmax
to I
LEDmin
.
I
LED
=((R2+R3)*V
FB
-R2*V
DC
)/(R3*R1);
R3=( V
DC
max
–V
FB)*
R2
/(
V
FB
*(1-I
LEDmin
/I
LEDmax
));
V
DC
= V
FB*
R3*(1+ R2/R3- I
LEDmin
/I
LEDmax
)/R2;
Example: V
DC
=5V, R2=5KOhm, R3=120KOhm
I
LEDmin
=17.5mA, when V
DC
=5V
I
LEDmax
=350mA, when V
DC
= V
FB
=200mV
The second dimming function is by PWM signal applied to FB pin. The PWM is the better way than analog
since the light color would not change but the intensity. Figure 3 shows the filtered PWM dimming circuit, which
replaces the DC source in figure 1. The PWM dimming circuit is suitable for high frequency PWM control signal.
LSP7502 Preliminary
2009/7/31
Liteon Semiconductor Corp.
*This is Preliminary Version. All the parameters may change.
4/4
LSP7502
20V/3A High Power LED Driver
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
+ n*Vf，in here, n is the LED numbers and Vf is the forward voltage of LED.
V
OUT
L1 Value
V
IN
=12V, I
MAX
=3A
3.5V
7.0V
33uH
47uH
10.5V
68uH
TEST CIRCUITS
1) Enable Function Test
2) Feedback Function Test
3) Operation Function Test
LSP7502 Preliminary
2009/7/31
Liteon Semiconductor Corp.
*This is Preliminary Version. All the parameters may change.
5/5
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