RT9277APF datasheet(4/12 Pages) RICHTEK

4 / 12 page

RT9277A/B

Preliminary

DS9277A/B-02 March 2007

www.richtek.com

Functional Pin Description

Pin No.

RT9277A

RT9277B

Pin Name

Pin Function

COMP

Compensation Pin for Error Amplifier. Connect a compensation network

ground.

See

the

Component

Selection

Table

for

the

loop

compensation.

Feedback Pin. Connect an external resistor-divider tap to FB. The typical

reference voltage is 1.24V.

Shutdown Control Input. Connect EN to GND to turn off the RT9277A/B.

GND

Ground

Switch Pin. Connect the inductor and catch diode to LX pin. Widen and

shorten the connected trace to minimize EMI.

VIN

Supply Pin. Place at least a 1

μF ceramic capacitor close to RT9277A/B

for bypassing noise.

FREQ

Frequency Select Pin. Oscillator frequency is 640kHz as FREQ

connected to GND, and 1.2MHz as FREQ connected to VIN. A 5

μA

pull-down current is sinking on this pin.

Soft-Start Control Pin. Connect a soft-start capacitor (CSS) to this pin. A

μA constant current charges the soft-start capacitor. When EN

connected to GND, the soft-start capacitor is discharged. When EN

connected to VIN high, the soft-start capacitor is charged to VIN. Leave

floating for not using soft-start.

No Connection

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