January 2003 AS80M1800/1801 ® EMI Reduction IC for Switching Power Supplies 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 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 Vout SS Modulated Gate Drive PWM Controller PWM_in AS80M1800 AS80M1801 MOSFET I_peak Current Sense Current Sense Sense Resistor Boost/Flyback configuration Alliance Semiconductor 2575 Augustine Drvie • Santa Clara, CA 95054 • Tel: 408.855.4900 • Fax: 408.855.4999 • www.alsc.com 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 lost 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 UVLO Spread range PWM_in 200 mA buffer Gate drive SS modulator Loss of drive detect Load monitor & recovery 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