UC2578

UC3578

05/99

FEATURES

• Provides Simple Single Inductor Buck

PWM Step-Down Voltage Regulation

• Drives External High Side NMOS

Switch

• 14V to 72V Input Voltage Operating

Range

• Contains 100kHz Internal Oscillator,

2V Reference and UVLO

• Soft Start on Power Up

• Overcurrent Shutdown Followed by

Soft Start

Buck Pulse Width Modulator Stepdown Voltage Regulator

14

16

11

15

10

7

6

2

3

13

12

5

4

EAINV

EAOUT

GND

GND

SRC

OUT

SS

CS

VCC

GND GND

DIODE

VGG

UC3578

C

SS

2200pF

100k

220pF

50k

R1

1k

5k

C

GG

1

µF

15

C

CC

1

µF

47

µF

10

1N4148

C

S

1000pF

R

S

1k

R

SENSE

0.12

IRFZ34

15-40 V

IN

1

µF

C

OUT

220

µF

L

OUT

40

µH

RECTIFIER

MBR 3100

V

OUT

TYPICAL APPLICATION DIAGRAM

UDG-99064

DESCRIPTION

The UC3578 is a PWM controller with an integrated high side floating gate

driver. It is used in buck step down converters and regulates a positive

output voltage. Intended to be used in a distributed power system, the IC

allows operation from 14V to 72V input voltage which range includes the

prevalent telecomm bus voltages. The output duty cycle of the UC3578

can vary between 0% and 90% for operation over the wide input voltage

and load conditions.

The UC3578 simplifies the design of the single switch PWM buck converter

by incorporating a floating high side driver for an external N-channel

MOSFET switch. It also features a 100kHz fixed frequency oscillator, an

internal 2V precision reference, an error amplifier configured for voltage

mode operation, and a PWM comparator with latching logic.

Comple-

menting the traditional voltage mode control block, the UC3578 incorpo-

rates an overcurrent shutdown circuit with full cycle soft re-start to limit the

input current to a user defined maximum value during overload operation.

Additional functions include an under voltage lockout circuit to insure that

sufficient input supply voltage is present before any switching activity can

occur.

The UC2578 and the UC3578 are both available in surface mount and

thru-hole power packages.

TEMPERATURE RANGE

PACKAGE

UC2578DP

–40°C to +85°C

Power SOIC

UC2578N

Power PDIP

UC3578DP

0°C to +70°C

Power SOIC

UC3578N

Power PDIP

ORDERING INFORMATION

application

INFO

available