MIC4043_11 Datasheet, PDF (5/12 Pages) MIC GROUP RECTIFIERS – Low-Voltage Secondary-Side Shunt Regulator Final Information

MIC4043
Functional Diagram
V_REF
1.245V
IN
SNK
MIC4043
FB
GND
Micrel
Functional Description
The MIC4043 combines a G_m amplifier, precision 1.245V
reference, and a pass transistor in a single package.
The operation of the MIC4043 is similar to conventional shunt
regulators such as the industry standard ’431. In a closed
loop system, the MIC4043 maintains the desired feedback
voltage at the FB pin by sinking current onto the SNK pin
proportional to the error voltage at the FB pin. The ratio of sink
current to error voltage is the transconductance of the device.
Reference
The MIC4043 uses a high-side reference. External voltage
dividers providing feedback to the MIC4043 will be inverted
when compared to those used with ’431-equivalent devices.
Behavior
The external feedback voltage is compared to the internal
high-side 1.245V reference.
If the feedback voltage, V_FB, is less than V_IN – V_REF, the
amplifier provides no drive to the sink transistor. If the
feedback voltages is greater than V_IN – V_REF, the amplifier
drives the pass transistor which sinks current to ground.
November 2000
5
MIC4043