RT7263B

3

DS7263B-01

September 2012

www.richtek.com

©

Copyright

2012 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

Function Block Diagram

Operation

The RT7263B is a constant frequency, current mode

synchronous step-down converter. In normal operation,

the high side N-MOSFET is turned on when the S-R latch

is set by the oscillator and is turned off when the current

comparator resets the S-R latch. While the high side

N-MOSFET is turned off, the low side N-MOSFET is turned

on to conduct the inductor current until next cycle begins.

Error Amplifier

The error amplifier adjusts its output voltage by comparing

the load current increases, it causes a drop in the feedback

voltage relative to the reference, the error amplifier's output

voltage then rises to allow higher inductor current to match

the load current.

Oscillator

The internal oscillator runs at fixed frequency 500kHz. In

short circuit condition, the frequency is reduced to 150kHz

for low power consumption.

Internal Regulator

The regulator provides low voltage power to supply the

internal control circuits and the bootstrap power for high

side gate driver.

Enable

The converter is turned on when the EN pin is higher than

2V. When the EN pin is lower than 0.4V, the converter will

enter shutdown mode and reduce the supply current to

be less than 1

μA.

Soft-Start (SS)

An internal current source charges an internal capacitor

to build a soft-start ramp voltage. The FB voltage will track

the internal ramp voltage during soft-start interval. The

typical soft-start time is 4ms.

UV Comparator

Comparator will go high to turn off the high side MOSFET.

The output under voltage protection is designed to operate

in Hiccup mode. When the UV condition is removed, the

converter will resume switching.

Thermal Shutdown

The over temperature protection function will shut down

the switching operation when the junction temperature

exceeds 150

°C. Once the junction temperature cools

down by approximately 30

°C, the converter will

automatically resume switching.

S

Q

R

Driver

-

+

Current Sense

Amplifier

PWM

Comparator

Oscillator

Ramp

Generator

Regulator

Reference

+

-

Error

Amplifier

SW

BOOT

FB

EN

VIN

GND

+

-

+

10µA

SS

VCC

400k

30pF

1pF

OC Limit

Clamp

SYNC