Micrel, Inc.

MIC2177

April 2008

3

M9999-042108

Pin Description

Pin Number

Pin Name

Pin Function

1, 2, 9

VIN

Supply Input: Controller and switch supply. Unregulated supply input to internal

regulator, output switches, and control circuitry. Requires bypass capacitor to PGND.

All three pins must be connected to VIN.

3, 8

SW

Switch (Output): Internal power MOSFET switch output. Both pins must be

externally connected together.

4, 5, 6, 7

PGND

Power Ground: Output stage ground connections. Connect all pins to a common

ground plane.

10

OUT

Output Voltage Sense (Input): Senses output voltage to determine minimum switch

current for PWM operation. Connect directly to VOUT.

11

AUTO

Automatic Mode: Connect 2.2nF timing capacitor for automatic PWM-/skip-mode

switching. Regulator operates exclusively in PWM mode when pin is pulled low.

12

FB

Feedback (Input): Error amplifier inverting input. For adjustable output version,

connect FB to external resistive divider to set output voltage. For 3.3V and 5V fixed

output versions, connect FB directly to output.

13

COMP

Compensation: Internal error amplifier output. Connect to capacitor or series RC

network to compensate the regulator control loop.

14, 15, 16, 17

SGND

Signal Ground: Ground connection of control section. Connect all pins to common

ground plane.

18

SYNC

Frequency Synchronization (Input): Optional clock input. Connect to external clock

signal to synchronize oscillator. Leading edge of signal above 1.7V terminates

switching cycle. Connect to SGND if not used.

19

BIAS

Bias Supply: Internal 3.3V bias supply output. Decouple with 0.01µF bypass

capacitor and 10kΩ to SGND. Do not apply any external load.

20

EN

Enable (Input): Logic high enables operation. Logic low shuts down regulator. Do

not allow pin to float.