© Semiconductor Components Industries, LLC, 2012

December, 2012 − Rev. 11

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 16V (on) and 10V (off), ideally

suited for off−line converters. The UCX845B is tailored for lower voltage

applications having UVLO thresholds of 8.5V (on) and 7.6V (off).

Features

Unique Site and Control Change Requirements; AEC−Q100

Qualified and PPAP Capable

Pin numbers in parenthesis are for the D suffix SOIC-14 package.

Output

Undervoltage

Lockout

GND

5.0V

Reference

Undervoltage

Lockout

Latching

PWM

Oscillator

Error

Amplifier

5(9)

3(5)

5(8)

6(10)

7(11)

Power

Ground

Current

Sense Input

1(1)

2(3)

4(7)

8(14)

Output/

Compensation

Voltage

Feedback

Input

7(12)

R

R

Figure 1. Simplified Block Diagram

14

SOIC−14

D SUFFIX

CASE 751A

1

See detailed ordering and shipping information in the package

dimensions section on page 15 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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