MIC2245

4MHz PWM Synchronous Buck

Regulator with LDO Standby Mode

Patent Pending

LOWQ

is a trademark of Micrel, Inc

MLF and MicroLeadFrame are trademarks of Amkor Technology, Inc

Micrel, Inc • 2180 Fortune Drive • San Jose, Ca 95131 • USA • tel +1 (408) 944-0800 • fax +1 (408) 474-1000 • http://www.micrel.com

January 2006

M9999-012406

www.micrel.com

General Description

The Micrel MIC2245 is a high efficiency 4MHz pulse

width modulated (PWM) synchronous buck (step-

down) regulator that features a LOWQ™ LDO

standby mode that draws only 18µA of quiescent

current. The MIC2245 allows an ultra-low noise,

small size, and high efficiency solution for portable

power applications.

In PWM mode, the MIC2245 operates with a

constant frequency 4MHz PWM control. Under light

load conditions, such as in system sleep or standby

modes, the PWM switching operation can be

disabled to reduce switching losses. In this light

load LOWQ™ mode, the LDO maintains the output

voltage and draws only 18µA of quiescent current.

The LDO mode of operation saves battery life while

not introducing spurious noise and high ripple as

experienced with pulse skipping or bursting mode

regulators.

The MIC2245 operates from a 2.7V to 5.5V input

voltage and features internal power MOSFETs that

can supply up to 500mA output current in PWM

mode. It can operate with a maximum duty cycle of

100% for use in low-dropout conditions.

The MIC2245 is available in the 10-pin 3mm x 3mm

MLF™ package with a junction operating range from

–40

°C to +125°C.

Data sheet and support documentation can be found

on Micrel’s web site at: www.micrel.com.

Features

• 2.7 to 5.5V supply/input voltage

• Light load LOWQ™ LDO mode

20µA quiescent current

Low noise, 75µVrms

• 4MHz PWM mode

Output current to 500mA

>92% efficiency

100% maximum duty cycle

• Adjustable output voltage option down to 1V

Fixed output voltage options available

• Ultra-fast transient response

• Uses a tiny 1µH inductor

• Fully integrated MOSFET switches

• Micropower shutdown operation

• Thermal shutdown and current limit protection

• Pb-free 10-pin 3mm x 3mm MLF™ package

• –40°C to +125°C junction temperature range

Applications

• Cellular phones

• PDAs

• USB peripherals

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Typical Application

Adjustable Output Buck Regulator with LOWQ™ Mode

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10

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30

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70

80

90

100

OUTPUT CURRENT (mA)

0

100

200

300

400

500