MIC4043 Low-Voltage, Secondary-Side Shunt Regulator General Description Features The MIC4043 is a shunt regulator optimized for secondaryside regulation in low-voltage power supplies. Featuring an output stage guaranteed to swing within 400mV of ground, the MIC4043 can be used in power supplies operating down to 1.8V, even with opto-isolators requiring greater than 1.2V of headroom. • Ideal for 1.8V switching converters • Low-voltage operation: − 400mV maximum saturation over operating temperature range • Easy-to-use − Voltage in, current out • 2% voltage tolerance over operating temperature range In power supply applications, the MIC4043 normally drives the LED of an optically isolated feedback circuit. The MIC4043 monitors a resistively-divided output voltage and sinks error current through the opto-isolator’s LED (secondary side); the opto-isolator’s transistor (primary side) provides this signal to the controller’s feedback input. The MIC4043 is also practical for other voltage-monitoring applications requiring an open-collector output. Applications • Optically-isolated, low-voltage power supplies • Low-voltage discrete regulator control The MIC4043 replaces conventional ’431-type shunt regulators to allow low-voltage applications where there is inadequate headroom for a 2.5V regulator in series with an opto-isolator. Replacing ’431-type devices requires only a minor change to the way that the resistive-divider values are calculated. Datasheets and support documentation are available on Micrel’s web site at: www.micrel.com. Typical Application 200kHz DC-to-DC Flyback Converter Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com October 10, 2014 Revision 2.0
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