RT9270 datasheet(3/13 Pages) RICHTEK

3 / 13 page

RT9270

Preliminary

DS9270-09 March 2007

www.richtek.com

Pin Description

COMP (Pin 1)

Compensation Pin for Error Amplifier. Connect a

compensation network to ground. See the Component

Selection Table for the loop compensation.

FB (Pin 2)

Feedback Pin. Connect an external resistor-divider tap to

FB. The reference voltage is 1.24V and set VOUT according

to: VOUT = 1.24V (1 + R1 / R2). See Figure 1.

EN (Pin 3)

Shutdown Control Input. Connect EN to GND to turn off

the RT9270.

GND (Pin 4)

Ground.

LX (Pin 5)

Switch Pin. Connect the inductor and catch diode to LX

pin. Widen and shorten the connected trace to minimize

EMI.

VIN (Pin 6)

Supply Pin. Place at least a 1uF ceramic capacitor close

to RT9270 for bypassing noise.

FREQ (Pin 7)

Frequency Select Pin. Oscillator frequency is 670kHz as

FREQ connected to GND, and 1.3MHz as FREQ

connected to VIN. A 5uA pull-down current is sinking on

this pin.

SS (Pin 8)

Soft-Start Control Pin. Connect a soft-start capacitor (CSS)

to this pin. A 4uA 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.

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