Datasheet MIC4043 (Micrel)

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