AS80M1800 ALSC | Alldatasheet
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EMI Reduction IC for Switching Power Supplies Notice: The information in this document is subject to change without notice. January 2003 ® Alliance Semiconductor 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
AS80M1800/1801 Product Brief 2003 (c) Copyright Alliance Semiconductor Corporation. All rights reserved. January 2003 Key Features
- Compatible with mo st 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 modulatio n 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 shut- ting off the output driver if the input PWM signal is lost
- Under voltage lock-out Protects SMPS from catastrophic failure by shut- ting off the output drive if the supply voltage drops below input VCC range
- Available in 8-pin SOIC package Device Block Diagram AS80M1800: 50 KHz to 400 KHz AS80M1801: 400 KHz to 1 MHz UVLO SS modulator 200 mA buffer Loss of drive detect Load monitor recovery Gate drive Current sense Current adjust Modulation rate Spread range PWM_in