RT9232BGS datasheet(3/14 Pages) RICHTEK

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RT9232B

DS9232B-03

March 2007

www.richtek.com

Function Block Diagram

Operation

Startup

RT9232B initializes automatically after receiving both VCC

and VIN power. Special power-on sequence is not

necessary. 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 OCSET pin. Voltage on

OCSET pin is a fixed voltage drop less than VIN. When

voltages on VCC, OCSET, and EN pins exceed their

thresholds, POR function initializes soft-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.

OCP

The OCP function monitors output current by using upper

MOSFET RDS(ON). The OCP function cycles soft-start

function in a hiccup mode. Overcurrent triggering level

can be arbitrarily set by adjusting ROCSET. An Internal 200

μA

current sink makes a voltage drop across ROCSET from

VIN. When VPHASE is lower than VOCSET, OCP function

initializes soft-start cycles. The soft-start function

discharges CSS with 10

μA current sink and disable PWM

function. Then soft-start function recharges Css and PWM

operation resumes. The soft-start hiccup restarts after

SS voltage fully charges to 4V if the output short event

still remains. The converter is shutdown permanently after

3 times hiccup and only restarting supply voltages can

enable the converter. The OCP funcion will be triggered

as inductor current reach :

OCSET

L(MAX)

DS(ON)

Power-On

Reset (POR)

Soft Start

and

Fault Logic

Oscillator

Driver Logic

PWM

10uA

Reference

GND

OCSET

PHASE

PVCC

LGATE

PGND

UGATE

BOOT

VCC

COMP

POR

0.6V

0.8V

INHIBIT

200uA

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