June 1998

1

MIC2178

MIC2178

Micrel

MIC2178

2.5A Synchronous Buck Regulator

General Description

The Micrel MIC2178 is a 200kHz synchronous buck (step-

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

tery-powered applications.

The MIC2178 operates from a 4.5V to 16.5V input and

features internal power MOSFETs that can supply up to 2.5A

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 MIC2178 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 MIC2178 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 MIC2178 and is packaged in a 20-lead wide power SOIC

package with an operating temperature range of –40

°C to

+85

°C.

See the MIC2177 for automatic selection of PWM or skip-

mode operation.

Typical Application

Features

• 4.5V to 16.5V input voltage range

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

PWM mode for > 200mA load current

Skip mode for < 200mA load current

• 100m

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

• Palmtop computers

• Laptop computers

• Cellular telephones

• Hand-held instruments

• Battery Chargers

BIAS

SGND

PWRGD

COMP

PGND

FB

SW

VIN

L1

33µH

C6

10nF

C5

0.01µF

MIC

2178-5.0

PWM

SYNC

EN

R1

20k

R2

15k

U1

20

11

10

18

13

14–17

19

12

4–7

3,8

1,2,9

D1

MBRS140

OUTPUT GOOD

OUTPUT LOW

C4

220µF

10V

5V/2.5A

C3

220µF

10V

6V to 16.5V

C1

22µF

35V

C2

22µF

35V

SKIP MODE

PWM MODE

70

75

80

85

90

95

100

10

100

1000 2500

OUTPUT CURRENT (mA)

5V Output

Efficiency

V

SKIP

PWM

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