ALSC AS80M1800

January 2003
EMI Reduction IC for Switching Power Supplies
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 electromagnetic 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
From Regulated Output
SS Modulated
Gate Drive
Current Sense
Current Sense
Boost/Flyback configuration
Alliance Semiconductor
2575 Augustine Drvie • Santa Clara, CA 95054 • Tel: 408.855.4900 • Fax: 408.855.4999 •
Notice: The information in this document is subject to change without notice.
January 2003
AS80M1800/1801 Product Brief
Key Features
Compatible with most PWM controllers
Works with both current mode and voltage mode
PWM controllers.
Input frequency ranges:
50 KHz to 400 KHz (AS80M1800)
400 KHz to 1 MHz (AS80M1801)
This is the input frequency range the device can
accommodate from the external PWM controller.
Wide input PWM duty cycle range of 10% to 90%
Supports an extremely wide range of line and load
regulation conditions.
Output drive current of 200 mA
Drives most popular power MOSFETs used in
SMPS designs.
Supply voltage range of 7 V to 20 V
Under voltage lockout
Spread spectrum modulation with adjustable spread
Output short circuit sense with adjustable level and
automatic recovery
No-load condition sense
Power savings feature
Frequency skip at no-load allows implementation
of Energy Star and other next generation power
savings modes
Loss of input detect
Protects SMPS from catastrophic failure by shutting off the output driver if the input PWM signal is
Under voltage lock-out
Protects SMPS from catastrophic failure by shutting off the output drive if the supply voltage drops
below input VCC range
Available in 8-pin SOIC package
Device Block Diagram
Modulation rate
Spread range
200 mA
Gate drive
Loss of
drive detect
Load monitor
AS80M1800: 50 KHz to 400 KHz
AS80M1801: 400 KHz to 1 MHz
Alliance Semiconductor
2003 (c) Copyright Alliance Semiconductor Corporation. All rights reserved.
Current sense
Current adjust