Sept25-07 Rev D

SP7601 29V High Voltage LED Driver

© 2007 Exar Corporation

Page 3

PIN DESCRIPTION

PIN #

PIN

NAME

DESCRIPTION

1

VIN

Input power supply for the controller. Place the input decoupling capacitor as

close as possible to this pin.

2

GATE

Connect to the gate terminal of the external P-channel MOSFET.

3

VDR

Power supply for the internal driver. This voltage is internally regulated to

close as possible to the IC.

4

FB

Regulator feedback input. A feedback resistor is connected between this pin

and the LED cathode. A current setting resistor is connected between the

cathode and ground of the LED. This pin can be also used for dimming control

and/or Power Sequencing.

5

GND

Ground pin.

6

LX

This pin is used as a current limit input for the internal current limit comparator.

Connect to the drain pin of the external MOSFET through an optional resistor.

Internal threshold is pre-set to 350mV nominal and can be decreased by

changing the external resistor based on the following formula:

BLOCK DIAGRAM

FAULT

Register

Set Dominant

POR

ENBL

4-Bit counter

VDR

VIN

GATE

5V Internal LDO

VIN - 0.35V

Overcurrent

Comparator

LX

VDR

33uA

GND

5V

+

-

+

-

VREF

FAULT

FB

Oscillator

VIN

S

R

I = k x VIN

Error Amplifier

PWM Comparator

PWM Latch

Reset Dominant

Vin - 5V LDO

FAULT

+

-

1V

FAULT

50ms delay

UVLO

S

R

R