RT9270PF 데이터 시트보기 (PDF) - Richtek Technology

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RT9270PF

High Performance, Low Noise Boost Converter

Richtek Technology 

RT9270

Function Block Diagram

Preliminary

EN

COMP

FB

FREQ

1.24V

LX

VIN

VFB

1.24

Protection

Error

Amplifier

-

+

Summing

Comparator

-

+

Clock

Enable

Control

and

Driver

Logic

Oscillator

5uA

Slope

Compen-

sation

Current

Sense

4uA

Soft-

Start

N

VIN

SS

LX

GND

Operation

The RT9270 is a high efficiency step-up Boost converter

with a fixed-frequency, current-mode PWM architecture.

It performs fast transient response and low noise operation

with appropriate component selection. The output voltage

is regulated through a feedback control consisting of an

error amplifier, a summing comparator, and several control

signal generators (as shown in function block diagram).

The feedback reference voltage is 1.24V. The error

amplifier varies the COMP voltage by sensing the FB pin.

The slope compensation signal summed with the current

-sense signal will be compared with the COMP voltage

through the summing comparator to determine the current

trip point and duty cycle. When driving light loads, the

RT9270 will perform the pulse-skipping mode to prevent

overcharging the output voltage. In this mode, the

switching frequency will be reduced to perform a higher

efficiency.

Soft-Start

The RT9270 provides soft-start function. When the EN pin

is connected to high, a 4uA constant current is sourced to

charge an external capacitor. The voltage rate of rise on

the COMP pin is limited during the charging period, and

so is the peak inductor current. When the EN pin is

connected to GND, the external capacitor will be

discharged to ground for the next time soft-start.

Current Limitation

The switch current is monitored to limit the value not to

exceed 1.9A typically. When the switch current reaches

1.9A, the output voltage will be pulled down to limit the

total output power to protect the power switch and external

components.

Shutdown

Connect the EN to GND to turn the RT9270 off and reduce

the supply current to 0.1uA. In this operation, the output

voltage is the value of VIN to subtract the forward voltage

of catch diode.

Frequency Selection

The switching frequency of RT9270 can be selected to

operate at either 670kHz or 1.3MHz. When the FREQ

pin is connected to GND for 670kHz operation, and

connected to VIN for 1.3MHz operation. FREQ is preset

to 670kHz operation for allowing the FREQ pin

unconnected.

www.richtek.com

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DS9270-09 March 2007

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