© Semiconductor Components Industries, LLC, 2004

September, 2004 − Rev. 3

1

Publication Order Number:

UC3844B/D

UC3844B, UC3845B,

UC2844B, UC2845B

High Performance

Current Mode Controllers

The UC3844B, UC3845B series are high performance fixed

frequency current mode controllers. They are specifically designed for

Off−Line and dc−dc converter applications offering the designer a

cost−effective solution with minimal external components. These

integrated circuits feature an oscillator, a temperature compensated

reference, high gain error amplifier, current sensing comparator, and a

high current totem pole output ideally suited for driving a power

MOSFET.

Also included are protective features consisting of input and

reference undervoltage lockouts each with hysteresis, cycle−by−cycle

current limiting, a latch for single pulse metering, and a flip−flop

which blanks the output off every other oscillator cycle, allowing

output deadtimes to be programmed from 50% to 70%.

These devices are available in an 8−pin dual−in−line and surface

mount (SOIC−8) plastic package as well as the 14−pin plastic surface

mount (SOIC−14). The SOIC−14 package has separate power and

ground pins for the totem pole output stage.

The UCX844B has UVLO thresholds of 16 V (on) and 10 V (off),

ideally suited for off−line converters. The UCX845B is tailored for

lower voltage applications having UVLO thresholds of 8.5 V (on) and

7.6 V (off).

Features

14

SOIC−14

D SUFFIX

CASE 751A

1

See detailed ordering and shipping information in the package

dimensions section on page 2 of this data sheet.

ORDERING INFORMATION

See general marking information in the device marking

section on page 16 of this data sheet.

DEVICE MARKING INFORMATION

1

8

PDIP−8

N SUFFIX

CASE 626

PIN CONNECTIONS

Compensation

NC

Voltage Feedback

NC

Current Sense

NC

Compensation

Voltage Feedback

Current Sense

NC

Output

GND

Power Ground

Output

GN

D

(Top View)

8

7

6

5

1

2

3

4

1

2

3

4

14

13

12

11

5

6

7

10

9

8

(Top View)

SOIC−8

D1 SUFFIX

CASE 751

1

8

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