1

www.semtech.com

SC4809A/B/C

High Performance Current Mode

PWM Controller

POWER MANAGEMENT

Revision: September 21, 2005

Description

Features

Applications

Typical Application Circuit

Operation to 1MHz

Accurate programmable maximum duty cycle

Line voltage monitoring

External frequency synchronization

Bi-phase mode of operation for low ripple

Under 100µA start-up current

Accessible reference voltage

VDD undervoltage lockout

-40°C to 105°C operating temperature

10 lead MSOP package. Lead free package available.

Fully WEEE and RoHS compliant

The SC4809A/B/C is a 10 pin BICMOS primary side

current mode controller for use in Isolated DC-DC and

off-line switching power supplies. It is a highly integrated

solution, requiring few external components. It features

a high frequency of operation, accurately programmable

maximum duty cycle, current mode control, line voltage

monitoring, supply UVLO, low start-up current, and

programmable soft start with user accessible reference.

It operates in a fixed frequency, highly desirable for

Telecom applications. Features a separate sync pin which

simplifies synchronization to an external clock. Feeding

the oscillator of one device to the sync of another forces

biphase operation which reduces input ripple and filter

size.

The SC4809A/B/C have different threshold and VREF

to accommodate a wide variety of applications.

These devices are available in the MSOP–10 lead free

package.

Telecom equipment and power supplies

Networking power supplies

Power over LAN applications

Industrial power supplies

Isolated power supplies

C1

C5

C4

+48V

-- 48V

R6

C2

R7

R2

U4

SC4431

VCC

3

OUT

4

IN

1

EN

5

GND

2

U2

SC1301

Q2

R11

R10

T1

C6

U3

R9

R3

R1

R12

D1

C7

D2

C8

C9

R14

R13

Vout

DISABLE

VDD

1

LUVLO

2

SYNC

3

RCT

4

FB

7

GND

8

OUT

9

VREF

10

DMAX

5

SS

6

U1

SC4809

SYNC

Q1

R4

R5

R8

C3