RT9277A/B

Preliminary

4

DS9277A/B-02 March 2007

www.richtek.com

Functional Pin Description

Pin No.

RT9277A

RT9277B

Pin Name

Pin Function

1

1

COMP

Compensation Pin for Error Amplifier. Connect a compensation network

to

ground.

See

the

Component

Selection

Table

for

the

loop

compensation.

2

2

FB

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

reference voltage is 1.24V.

3

3

EN

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

4

4

GND

Ground

5

5

LX

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

shorten the connected trace to minimize EMI.

6

6

VIN

Supply Pin. Place at least a 1

μF ceramic capacitor close to RT9277A/B

for bypassing noise.

7

7

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.

--

8

SS

4

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.

8

--

NC

No Connection