Philips Semiconductors Linear Products

Product specification

UC3842

Current-mode PWM controller

1100

August 31, 1994

853-0614 13721

DESCRIPTION

The UC3842 is available in an 8-Pin mini-DIP the necessary

features to implement off-line, fixed-frequency current-mode control

schemes with a minimal external parts count. This technique results

in improved line regulation, enhanced load response characteristics,

and a simpler, easier to design control loop. Topological advantages

include inherent pulse-by-pulse current limiting.

Protection circuitry includes built-in undervoltage lock-out and

current limiting. Other features include fully-latched operation, a 1%

trimmed bandgap reference, and start-up current less than 1mA.

These devices feature a totem-pole output designed to source and

sink high peak current from a capacitive load, such as the gate of a

power MOSFET. Consistent with N-channel power devices, the

output is low in the OFF-state.

FEATURES

PIN CONFIGURATIONS

N Package

D Package

1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

8

14

13

12

11

10

9

COMP

NC

COMP

VFB

ISENSE

RT/CT

VFB

ISENSE

RT/CT

NC

NC

VREF

VCC

OUTPUT

GROUND

NC

VREF

VCC

OUTPUT

GROUND

VC

POWER GROUND

TOP VIEW

TOP VIEW

APPLICATIONS

BLOCK DIAGRAM

NOTE:

Pin numbers in parentheses refer to the D package.

(12)7

(9)5

(7)4

(3)2

(1)1

(5)3

7(11)

8(14)

6(10)

5(8)

GND

COMP

CURRENT

SENSE

CURRENT

SENSE

COMPARATOR

PWM

LATCH

INTERNAL

BIAS

5V

REF

UVLO

34V

16V

OSC

ERROR

AMP

+

–

2R

R

1V

2.5V

5.0V

50mA

OUTPUT

6V

VREF

VCC

VFB

S/R

RT/CT

S

R