Date: 5/25/04

SP6121 Low Voltage, Synchronous Step Down PWM Controller

© Copyright 2004 Sipex Corporation

1

SP6121

■ Optimized for Single Input Voltage - 3V to 5.5V

■ High Efficiency: Greater than 95% possible

■ Accurate, 500kHz Fixed Frequency Operation

■ Fast Transient Response

■ Internal, 0.4 V/ms, Soft Start Circuit

■ Precision 1% Reference

■ Resistor Programmable Output Voltage

■ Lossless Adjustable Current Limit with

■ 0% to 100% Duty Cycle Range

■ High Side PMOS Switch Negates Need for

■ External Charge Pump

■ Output Over Voltage Protection

■ Hiccup Mode Current Limit Protection

Low Voltage, Synchronous Step Down PWM Controller

Ideal for 2A to 10A, Small Footprint, DC-DC Power Converters

APPLICATIONS

■ Supply Bias for

- DSP

- Microprocessor Core

- I/O & Logic

■ Video Cards

■ Board Level Supply in

Distributed Power Systems

®

DESCRIPTION

The SP6121 is a fixed frequency, voltage mode, synchronous PWM controller designed to work

from a single 5V or 3.3V input supply, providing excellent AC and DC regulation for high efficiency

power conversion. The operating frequency is internally set at 500kHz, permitting the use of

small, surface mount inductors and capacitors. Requiring only few external components, the

SP6121 packaged in an 8-pin SOIC, is especially suited for low voltage applications where cost,

small size and high efficiency are critical. With its low voltage capability and inherent 100% duty

cycle operation, the SP6121 allows low dropout operation in the event of a low input supply

voltage condition.

Q1 = FAIRCHILD FDS6375

Q2 = FAIRCHILD FDS6690A

DS = STMICROELECTRONICS STPS2L25BU

L1 = PANASONIC ETQ-P6F1R6SFA

C

1

2

3

4

5

6

7

8

COMP

GND

PDRV

NDRV

SP6121

8 Pin SOIC

CB

3.3µF

47µF

Ceramic 6.3V

3.3V

PDRV

GND

COMP

SP6121

U1

®

®

NDRV

CP

50pF

RZ

10k

1.8µH

L1

470µF x 2

RSET

2.3k

1.9V 8A

Q1

CZ

3.7nF

Q2

5

DS

R1

5.2k

R2

10k

FEATURES

TYPICAL APPLICATION CIRCUIT

Now Available in Lead Free Packaging