June 1998

1

MIC2179

MIC2179

Micrel

MIC2179

1.5A Synchronous Buck Regulator

General Description

The Micrel MIC2179 is a 200kHz synchronous buck (step-

down) switching regulator designed for high-efficiency, bat-

tery-powered applications.

The MIC2179 operates from a 4.5V to 16.5V input and

features internal power MOSFETs that can supply up to 1.5A

output current. It can operate with a maximum duty cycle of

100% for use in low-dropout conditions. It also features a

shutdown mode that reduces quiescent current to less than

5

µA.

The MIC2179 achieves high efficiency over a wide output

current range by operating in either PWM or skip mode. The

operating mode is externally selected, typically by an intelli-

gent system, which chooses the appropriate mode according

to operating conditions, efficiency, and noise requirements.

The switching frequency is preset to 200kHz and can be

synchronized to an external clock signal of up to 300kHz.

The MIC2179 uses current-mode control with internal current

sensing. Current-mode control provides superior line regula-

tion and makes the regulator control loop easy to compen-

sate. The output is protected with pulse-by-pulse current

limiting and thermal shutdown. Undervoltage lockout turns

the output off when the input voltage is less than 4.5V.

The MIC2179 and is packaged in a 20-lead SSOP package

with an operating temperature range of –40

°C to +85°C.

Typical Application

BIAS

SGND

COMP

PGND

FB

SW

VIN

C2

100µF

6.3V

3.3V/600mA

L1

22µH

C4

6.8nF

C3

0.01µF

MIC

2179-3.3

PWM

Skip Mode

PWM Mode

SYNC

EN

R2

10k

5.4V to 16.5V

C1

10µF

20V

U1

15

5

13

8

9–12

14

7

1,2,

19,20

3,4

16,17

D1

MBRM120

PWRGD

6

R1

20k

Output Good

Output Low

Pins 4 and 18 are not connected.

Pins 3 and 4 can be connected

together for a low-impedance

connection.

Features

• 4.5V to 16.5V input voltage range

• Dual-mode operation for high efficiency (up to 96%)

PWM mode for > 150mA load current

Skip mode for <150mA load current

• 150m

Ω internal power MOSFETs at 12V input

• 200kHz preset switching frequency

• Low quiescent current

1.0mA in PWM mode

600

µA in skip mode

< 5

µA in shutdown mode

• Current-mode control

Simplified loop compensation

Superior line regulation

• 100% duty cycle for low dropout operation

• Current limit

• Thermal shutdown

• Undervoltage lockout

Applications

• High-efficiency, battery-powered supplies

• Buck (step-down) dc-to-dc converters

• Cellular telephones

• Laptop computers

• Hand-held instruments

• Battery Charger

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com