1

ASTEC Semiconductor

AS384x

Current Mode Controller

Features

1.0% and temperature-compensated

to 105¡C

precision duty cycle clamp

cycle clamp

synchronization

hysteresis provide more predictable

start-up and shutdown

AC noise immunity

sense pulled below ground

Description

The AS3842 family of control ICs provide pin-for-pin replacement of the

industry standard UC3842 series of devices. The devices are

redesigned to provide significantly improved tolerances in power sup-

ply manufacturing. The 2.5 V reference has been trimmed to 1.0%

tolerance. The oscillator discharge current is trimmed to provide guar-

anteed duty cycle clamping rather than specified discharge current.

The circuit is more completely specified to guarantee all parameters

impacting power supply manufacturing tolerances.

In addition, the oscillator and flip-flop sections have been enhanced to

chronization input that can be easily driven from open collector/open

drain logic outputs. This sync input is a high impedance input and can

easily be used for externally clocked systems. The new flip-flop topol-

ogy allows the duty cycle on the AS3844/5 to be guaranteed between

49 and 50%. The AS3843/5 requires less than 0.5 mA of start-up cur-

rent over the full temperature range.

SEMICONDUCTOR

14L SOIC (D14)

8L SOIC (D8)

1

2

3

4

8

7

6

5

V

REG

V

CC

OUT

GND

COMP

V

FB

I

SENSE

R

V

REG

NC

V

CC

V

C

COMP

NC

V

FB

OUT

PWR G

GND

I

SENSE

NC

R

NC

PDIP (N)

V

REG

V

CC

OUT

GND

COMP

V

FB

I

SENSE

R

1

2

3

4

8

7

6

5

1

2

3

5

6

7

4

14

13

12

11

10

9

8

Circuit Type:

Current Mode Controller (See Table A)

Package Style

D8 =

D14 =

N =

8

14

8

Pin Plastic SOIC

Pin Plastic SOIC

Pin Plastic DIP

AS384X

D8

13

Packaging Option:

T

13

= Tube

= Tape and Reel (13" Reel Dia)

Ordering Information

Table A

Duty Cycle

Model

V

CC(min)

V

CC(on)

Typ.

I

CC

AS3842

10

16

97%

0.5 mA

AS3843

7.6

8.4

97%

0.3 mA

AS3844

10

16

49.5%

0.5 mA

AS3845

7.6

8.4

49.5%

0.3 mA