MIC4043_11 Datasheet, PDF (1/12 Pages) MIC GROUP RECTIFIERS – Low-Voltage Secondary-Side Shunt Regulator Final Information

MIC4043
Micrel
MIC4043
Low-Voltage Secondary-Side Shunt Regulator
Final Information
General Description
The MIC4043 is a shunt regulator optimized for secondary-
side 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 optoisolators requiring greater than 1.2V of
headroom.
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 optoisolator’s LED (secondary side); the
optoisolator’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.
The MIC4043 replaces conventional ’431-type shunt regula-
tors to allow low-voltage applications where there is inad-
equate headroom for a 2.5V regulator in series with an
optoisolator. Replacing ’431-type devices requires only a
minor change to the way that the resistive-divider values are
calculated.
Features
• 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
Applications
• Optically isolated low-volage power supplies
• Low-voltage discrete regulator control
Typical Application
OPTICAL
ISOLATION
MIC4043
IN SNK
GND FB
MIC4043
V_IN
Low-Side Feedback
Control
COMPENSATION
1
7
V_OUT
R1
MIC38HC43BN
1 _{COMP VREF} 8
2 _FB
V_DD ⁷
3 _ISNS
V_OUT ⁶
4 _{RT/CT GND} 5
2
6
4
3
R2
Return
V_OUT
=
1.245V

R2
R1
+ 1^{}
200kHz DC-DC Flyback Converter
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com
November 2000
1
MIC4043