1

LT1241 Series

The LT

current mode, pulse width modulators. They are improved

plug compatible versions of the industry standard UC1842

series. These devices have both improved speed and

lower quiescent current. The LT1241 series is optimized

for off-line and DC/DC converter applications. They con-

tain a temperature-compensated reference, high gain er-

ror amplifier, current sensing comparator and a high

current totem pole output stage ideally suited to driving

power MOSFETs. Start-up current has been reduced to

less than 250

µA. Cross-conduction current spikes in

the output stage have been eliminated, making 500kHz

operation practical. Several new features have been incor-

porated. Leading edge blanking has been added to the

current sense comparator. Trims have been added to the

oscillator circuit for both frequency and sink current, and

both of these parameters are tightly specified. The output

on state. The output and the reference output are actively

pulled low during undervoltage lockout.

High Speed Current Mode

Pulse Width Modulators

s

Low Start-Up Current: < 250

µA

s

50ns Current Sense Delay

s

Current Mode Operation: To 500kHz

s

Pin Compatible with UC1842 Series

s

Undervoltage Lockout with Hysteresis

s

No Cross-Conduction Current

s

Trimmed Bandgap Reference

s

1A Totem Pole Output

s

Trimmed Oscillator Frequency and Sink Current

s

Active Pull-Down on Reference and Output During

Undervoltage Lockout

s

High Level Output Clamp: 18V

s

Current Sense Leading Edge Blanking

DESCRIPTIO

S

FEATURE

S

APPLICATI

s

Off-Line Converters

s

DC/DC Converters

, LTC and LT are registered trademarks of Linear Technology Corporation.

+

–

+

–

1

2

FB

COMP

2.5V

2R

R

1V

1.5V

–

+

3

BLANKING

1mA

5.6V

4

OSCILLATOR

R

S

18V

5

GND

6

OUTPUT

8

5V REF

MAIN BIAS

REFERENCE PULL-DOWN

OUTPUT

PULL-DOWN

REFERENCE ENABLE

1241 BD01

T

UV

LOCKOUT

I

DAGRA

BLOCK