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