November 2000

5

MIC4043

MIC4043

Micrel

Functional Diagram

SNK

FB

IN

1.245V

GND

MIC4043

Functional Description

The MIC4043 combines a G

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

amplifier provides no drive to the sink transistor. If the

feedback voltages is greater than V

drives the pass transistor which sinks current to ground.