RT8289

2

DS8289-01 March 2011

www.richtek.com

Functional Pin Description

Function Block Diagram

Pin No.

Pin Name

Pin Function

1

BOOT

High Side Gate Drive Bootstrap Input. BOOT supplies the drive for the high side

N-MOSFET switch. Connect a 10nF or greater capacitor from SW to BOOT to

power the high side switch.

2, 3

NC

No Internal Connection.

4

FB

Feedback Input. FB senses the output voltage to regulate said voltage. Drive FB

with a resistive voltage divider from the output voltage. The value of the divider

resistors also sets loop bandwidth. The feedback threshold is 1.222V.

5

EN

Chip Enable (Active High). EN is a digital input that turns the regulator on or off.

Drive EN higher than 1.4V to turn on the regulator, lower than 0.4V to turn it off.

For automatic startup, leave EN unconnected.

6,

9 (Exposed Pad)

GND

Ground. The exposed pad must be soldered to a large PCB and connected to

GND for maximum power dissipation.

7

VIN

Power Input. VIN supplies the power to the IC, as well as the step-down

GND with a suitably large capacitor to eliminate noise on the input to the IC.

8

SW

Power Switching Output. SW is the switching node that supplies power to the

output. Connect the output LC filter from SW to the output load. Note that a

capacitor is required from SW to BOOT to power the high side switch.

S

Q

R

Driver

Bootstrap

Control

-

+

Current Sense

Amplifier

PWM

Comparator

Oscillator

500kHz

Ramp

Generator

Regulator

Reference

+

-

12k

Error

Amplifier

30pF

400k

13pF

SW

BOOT

FB

EN

VIN

GND

+

-

OC Limit

Clamp