MIC2172/3172

Micrel

4-14

1997

Ordering Information

Part Number

Temperature Range

Package

MIC2172BN

–40

°C to +85°C

8-pin plastic DIP

MIC2172BM

–40

°C to +85°C

8-lead SOIC

MIC3172BN

–40

°C to +85°C

8-pin plastic DIP

MIC3172BM

–40

°C to +85°C

8-lead SOIC

8-lead SOIC (M)

8-lead DIP (N)

1

2

3

4

S GND

COMP

P GND 1

FB

P GND 2

8

7

6

5

Pin Configuration

1

2

3

4

S GND

COMP

P GND 1

FB

P GND 2

8

7

6

5

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

Enable: Apply TTL high or connect to V

TTL low or connect to ground to disable the regulator. Device draws only

leakage current (<1

µA) when disabled.

5V

IN

Supply Voltage: 3.0V to 40V

6

P GND 2

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

Ω current

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

voltage ground depending on circuit topology.

7V

SW

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

Ω current

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

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