RT9232

3

DS9232-06 March 2007

www.richtek.com

Function Block Diagram

Operation

Startup

The Power-On Reset (POR) function continually monitors input supply voltages and enable voltage. POR function

monitors IC power via VCC pin and external MOSFET power via SENSE pin. Voltage on SENSE pin is a fixed voltage

start operation. POR inhibits driver operation while EN pin pulls low. Transitioning EN pin high after input supply voltages

ready initializes soft-start operation.

Soft-Start

After POR function releases soft-start operation, an internal 10uA current source charges an external capacitor on SS

pin (Css) to 5V. Soft-start function clamps both COMP & FB pins to SS pin voltage & a fixed voltage drop less than SS

pin voltage respectively. Thus upper MOSFET turns on at a limited duty and output current overshoot can be reduced.

This method provides a rapid and controlled output voltage rise.

Under Voltage Protection

The under voltage protection function protects the converter from an shorted output by detecting the voltage on FB pin

to monitor the output voltage. The UVP function cycles soft-start function in a hiccup mode. When output voltage lower

than 75% of designated voltage, UVP function initializes soft-start cycles. The soft-start function discharges Css with

10uA current sink and disable PWM operation. Then soft-start function recharges Css and PWM operation resumes.

shutdown permanently after 3 times hiccup and only restarting supply voltages can enable the converter.

Power-On

Reset (POR)

Soft Start

and

Fault Logic

Oscillator

Driver Logic

EA

PWM

10uA

Reference

SS

GND

FB

SENSE

PHASE

PVCC

LGATE

PGND

UGATE

BOOT

VCC

COMP

RT

POR

V

IN

POR

-

+

+

-

-

+

+

-

0.6V

UV

0.8V

EN

INHIBIT

1.5V

+

+