3

FR9765-1.0-MAR-2012

FR9765

85T

fitipower integrated technology lnc.

Functional Pin Description

Pin Name

Pin No.

Pin Function

BS

1

High Side Gate Drive Boost Input.

A 10nF or greater capacitor must be connected from this pin to SW.

It can boost the gate drive to fully turn on the internal high side NMOS.

VIN

2

Power Supply Input Pin.

Drive 4.75V to 24V voltage to this pin to power on this chip.

Connect two

22μF ceramic bypass capacitors between VIN and GND to eliminate noise.

SW

3

Power Switching Output.

It is the output pin of internal high side NMOS which is the switch to supply

power.

GND

4

Ground Pin.

Connect this pin to exposed pad.

FB

5

Voltage Feedback Input Pin.

Connect FB and VOUT with a resistive voltage divider.

This IC senses

feedback voltage via FB and regulates it at 0.925V.

COMP

6

Compensation Pin.

This pin is used to compensate the regulation control loop.

Connect a series RC

network from COMP pin to GND.

EN

7

Enable Input Pin.

This pin provides a digital control to turn the converter on or off.

For automatic

startup, leave EN unconnected.

SS

8

Soft-Start Input Pin.

This pin controls the soft-start period.

Connect a capacitor from SS to GND to

set the soft start period.

Block Diagram

Oscillator

180KHZ / 1.4MHZ

REGULATOR

FB

COMP

EN

VIN

BS

SW

GND

VIN UVLO

6μA

OTP

CLK

0.5V

+

Error

Amplifier

0.925V

Current Sense

Amplifier

+

SS

Current

Comparator

2.5V

1μA

1.4V

S

R

Q

Q

SET

CLR

6.5V

High-Side

MOSFET

Low-Side

MOSFET

Figure 5. Block Diagram of FR9765