1

Features

Gnd

COMP

OSC

Sense

Undervoltage

Lockout

Internal

Bias

NOR

S

R

PWM

Latch

Current

Sensing

Comparator

R

2 R

1V

Error

Amplifier

-

+

2.50V

Set/

Reset

34V

16V/10V

(8.4V/7.6V)

R

R

Pwr Gnd

Oscillator

Toggle

Flip-Flop

5.0 Volt

Reference

( ) indicates CS-2845/3845

s

Optimized for Offline

Control

s

Temp. Compensated

Oscillator

s

50% Max Duty-cycle Clamp

s

Output Stage is Enabled

s

Low Start-up Current

s

Pulse-by-pulse Current

Limiting

s

Improved Undervoltage

Lockout

s

Double Pulse Suppression

s

1% Trimmed Bandgap Ref.

s

High Current Totem Pole

Output

Package Options

Current Mode PWM Control Circuit

with 50% Max Duty Cycle

CS2844/CS3844

CS2845/CS3845

Description

Block Diagram

Absolute Maximum Ratings

Supply Voltage (Low Impedance Source) .................................................................30V

Output Current..............................................................................................................±1A

Output Energy (Capacitive Load) ................................................................................5µJ

Error Amp Output Sink Current .............................................................................10mA

Lead Temperature Soldering

Wave Solder (through hole styles only) ...................10 sec. max, 260°C peak

Reflow (SMD styles only) ....................60 sec. max above 183°C, 230°C peak

1

COMP

2

3

4

Sense

OSC

Gnd

8

7

6

5

8 Lead PDIP & SO Narrow

10

7

14

13

12

8

1

2

3

4

5

6

11

9

COMP

NC

NC

Sense

NC

OSC

NC

Pwr Gnd

Gnd

14 Lead SO Narrow

The CS3844/45 provides all the neces-

sary features to implement off-line

fixed frequency current-mode control

with a minimum number of external

components.

The CS3844 family incorporates a new

precision temperature-controlled oscil-

lator to minimize variations in fre-

quency. An internal toggle flip-flop,

which blanks the output every other

clock cycle, limits the duty-cycle range

to less than 50%. An undervoltage

before the output stage is enabled. In

the CS2844/CS3844 turn on occurs at

16V and turn off at 10V. In the

CS2845/CS3845 turn on is at 8.4V and

turn off at 7.6V.

Other features include low start-up

current, pulse-by-pulse current limit-

ing, and a high-current totem pole out-

put for driving capacitive loads, such

as gate of a power MOSFET. The out-

put is low in the off state, consistent

with N-channel devices.

16

15

14

13

12

11

11

10

9

1

2

3

4

5

6

7

8

NC

NC

COMP

SENSE

OSC

NC

NC

NC

Gnd

Pwr Gnd

NC

16 Lead SO Wide

Cherry Semiconductor Corporation

2000 South County Trail, East Greenwich, RI 02818

Tel: (401)885-3600 Fax: (401)885-5786

Email: info@cherry-semi.com

Web Site: www.cherry-semi.com

A

Company

®

Rev. 3/17/99