3

DS8577-00 November 2011

www.richtek.com

RT8577

Functional Pin Description

Pin No.

Pin Name

Pin Function

1

LED2

Channel 2 LED Current Sink, Leave this pin unconnected if it is not used.

2

LED1

Channel 1 LED Current Sink, Leave this pin unconnected if it is not used.

3, 17, 18,

21 (Exposed pad)

GND

Ground. The exposed pad must be soldered to a large PCB and connected to

GND for maximum power dissipation.

4

OVP/UVP

Over Voltage and Under Voltage Protection. PWM boost converter turns off

5

RISET

LED Current Set Pin. A resistor or a current from DAC on this pin programs the

full LED current.

6

PWM

Dimming Control Input.

7

STATUS

Boost Converter Operation Status Output.

8

RT

Switching Frequency Set. Connect a resistor between RT and GND to set the

boost converter switching frequency.

9

VC

PWM Boost Converter Loop Compensation Node.

10

SS

Soft-Start Pin. Place a capacitor of at least 10nF from this pin to GND to set the

soft-start time period.

11

EN

Chip Enable. When EN is pulled low, the chip will be shut down.

12

SEN

Current Sense Input. During normal operation, this pin senses the voltage

across the external inductor current sensing resistor for peak current mode

control and also to limit the inductor current during every switching cycle.

13

PGND

Boost Converter Power Ground.

14

DRV

Boost Converter Power Switch Gate Output. This pin drives the external power

N-MOSFET device.

15

CREG

1

μF capacitor should be placed on this pin to stabilize the 5V output of the

internal regulator. This regulator is for chip internal use only.

16

VCC

Power Supply of the Chip. For good bypass, a low ESR capacitor close to the

pin is required.

19, 20

LED4, LED3 Channel 4 and 3 LED Current Sinks. Leave the pins unconnected if not used.