MIC4043 Low-Voltage, Secondary-Side Shunt Regulator General Description Features The MIC4043 is a shunt regulator optimized for secondary- Ideal for 1.8V switching converters side regulation in low-voltage power supplies. Featuring an Low-voltage operation: output stage guaranteed to swing within 400mV of ground, 400mV maximum saturation over operating the MIC4043 can be used in power supplies operating temperature range down to 1.8V, even with opto-isolators requiring greater Easy-to-use than 1.2V of headroom. Voltage in, current out In power supply applications, the MIC4043 normally drives 2% voltage tolerance over operating temperature range the LED of an optically isolated feedback circuit. The MIC4043 monitors a resistively-divided output voltage and Applications sinks error current through the opto-isolators LED (secondary side) the opto-isolators transistor (primary Optically-isolated, low-voltage power supplies side) provides this signal to the controllers feedback input. Low-voltage discrete regulator control The MIC4043 is also practical for other voltage-monitoring applications requiring an open- collector output. 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 Micrels 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 Micrel, Inc. MIC4043 Ordering Information (1) Part Number Marking Voltage (V) Tolerance Configuration Temperature Range Package MIC4043YM4 RB1D 1.245 1% Open Collector 40C to +85C SOT-143 Note: 1. Underbar ( ) symbol may not be to scale. Pin Configuration SOT-143 (M4) (Top View) Pin Description Pin Number Pin Name Pin Function 1 IN Input: Supply voltage input. 2 SNK Sink (Output): NPN open collector output. 3 GND Ground 4 FB Feedback (Input): Feedback input from external voltage-divider network. October 10, 2014 Revision 2.0 2