AS80M1800/1801

EMI Reduction IC for Switching Power Supplies

Notice: The information in this document is subject to change without notice.

January 2003

®

Alliance Semiconductor

2575 Augustine Drvie • Santa Clara, CA 95054 • Tel: 408.855.4900 • Fax: 408.855.4999 • www.alsc.com

Overview

AS80M1800 and AS80M1801 are programmable spread

spectrum frequency modulators designed for Switched

Mode Power Supply (SMPS) applications. These devices

work as companion ICs to the pulse width modulation

(PWM) controller. As such, they can be used as a simple

drop-in solution between the PWM controller and

MOSFET to tackle most EMI problems in the SMPS.

The AS80M1800 and AS80M1801 reduce electro-

magnetic interference (EMI) by applying spread spectrum

modulation to the PWM gate drive signal at the gate of the

power MOSFET. Gate drive modulation significantly

reduces the conducted and radiated emissions usually

generated by di/dt and dv/dt switching in a SMPS.

These are the first general purpose EMI reduction ICs

specifically designed for use in SMPS systems. No other

manufacturer to date has a device that can frequency

modulate a PWM train and still maintain the input PWM

content. They can be used in popular DC/DC converter,

and AC/DC inverter and DC/AC inverters designs.

Besides providing EMI reduction functionality, the

AS80M1800 and AS80M1801 provide additional features

that extend the capabilities of the power system.

Simplified Application Diagram

PWM

Controller

AS80M1800

AS80M1801

SS Modulated

Gate Drive

Current Sense

PWM_in

Current Sense

Vout

I_peak

MOSFET

Sense

Resistor

From Regulated Output

Boost/Flyback configuration