Micrel

MIC2172/3172

April 2006

3

M9999-041806

(408) 955-1690

Pin Description

Pin Number

Pin Name

Pin Function

1

S GND

Signal Ground: Internal analog circuit ground. Connect directly to the input filter

capacitor for proper operation (see applications info). Keep separate from power

grounds.

2

COMP

Frequency Compensation: Output of transconductance type error amplifier.

Primary function is for loop stabilization. Can also be used for output voltage

soft-start and current limit tailoring.

3

FB

Feedback: Inverting input of error amplifier. Connect to external resistive divider

to set power supply output voltage.

4 (MIC2172)

SYNC

Synchronization/Frequency Adjust: Capacitively coupled input signal greater

than device’s free running frequency (up to 135kHz) will lock device’s oscillator

on falling edge. Oscillator frequency can be trimmed up to 135kHz by adding a

resistor to ground. If unused, pin must float (no connection).

4 (MIC3172)

EN

or connect to ground to disable the regulator. Device draws only leakage current

(<1µA) when disabled.

5

VIN

Supply Voltage: 3.0V to 40V

6

P GND 2

Power Ground #2: One of two NPN power switch emitters with 0.3

sense resistor in series. Required. Connect to external inductor or input voltage

ground depending on circuit topology.

7

VSW

Power Switch Collector: Collector of NPN switch. Connect to external inductor or

input voltage depending on circuit topology.

8

P GND 1

Power Ground #1: One of two NPN power switch emitters with 0.3

sense resistor in series. Optional. For maximum power capability connect to P

GND 2. Floating pin reduces current limit by a factor of two.