1

1.25A High Efficiency Switching Regulator

CS3972

Description

Block Diagram

Features

s

Switch

s

3V to 60V Input Voltage

Range

s

6mA Input Supply

Current

s

1.24V Precision Reference

s

40kHz Switching

Frequency

s

Variable Current Limit

with External Voltage

Clamp

s

Under-Voltage Protection

s

Over-Temperature

Protection

s

External Synchronization

Package Options

5L TO-220

Tab (Gnd)

8L PDIP

1

Gnd

NC

1

3 Gnd

16L SO Wide

1

Gnd

NC

NC

NC

NC

NC

NC

NC

NC

NC

December, 2001 - Rev. 9

ON Semiconductor

2000 South County Trail, East Greenwich, RI 02818

Tel: (401)885–3600 Fax: (401)885–5786

N. American Technical Support: 800-282-9855

Web Site: www.cherry–semi.com

The CS3972 is a 1.25A, 60V, current

mode, high efficiency, switching

regulator circuit. It can be config-

ured in buck, boost, forward, iso-

lated and non-isolated topologies,

using a single-ended switch.

The IC contains a 1.25A high effi-

ciency output switch, precision

bandgap reference, voltage regula-

tor, error amplifier, oscillator, con-

trol, and protection circuitry.

Output transistor efficiency is

achieved by keeping the switch in

quasi-saturation when it is on. This

minimizes the switch turn-off

delay time and power dissipation,

an important consideration for

applications with wide ranging

loads.

The precision reference is internally

trimmed to 1.24V, while the oscilla-

tor frequency is internally trimmed

to 40kHz. The on board 2.3V regu-

lator powers the internal circuitry.

By keeping the voltage regulator at

2.3V, the IC is able to operate down

to 3V and maintain a constant input

supply current of 6mA(typ).

Synchronization mode is achieved

of less than 0.2V with a duration of

ing frequency can be adjusted from

50kHz to 70kHz. The IC's synchro-

nization mode is set externally.

Protection circuitry includes a vari-

able current limit with external

voltage clamp, under-voltage and

over-temperature protection.

Output

Protection

Driver

2.3V

Reg

Logic

40kHz

OSC

Error

Amp

-

+

1.24V

Ref

Current

Amp

-

+

VSW

VC

VIN

VFB

0.22

Ω

0.22

Ω

COMP

E1*

E2*

Gnd

*Always connect E1 to Ground Pin on DIP package. Both emitters are tied to ground on TO-220 Package.

1.25A,

75V

Switch

-

+