August, 2004

1

M9999-081104

MIC2291

Micrel

MIC2291

1.2A PWM Boost Regulator

Photo Flash LED Driver

General Description

The MIC2291 is a 1.2MHz Pulse Width Modulation (PWM),

boost-switching regulator that is optimized for high-current,

white LED photo flash applications. With a guaranteed switch

current of 1.2A, the MIC2291 easily drives a string of 3 white

LEDs in series at 100mA, ensuring a high level of brightness

and eliminating several ballast resistors.

The MIC2291 implements a constant frequency, 1.2MHz

PWM control scheme. The high frequency PWM operation

saves board space by reducing external component sizes.

The added benefit of the constant frequency PWM scheme,

in contrast to variable frequency topologies, is much lower

noise and input ripple injected back to the battery source.

To optimize efficiency, the feedback voltage is set to only

95mV. This reduces the power dissipation in the current set

resistor, and allows the lowest total output voltage, hence

minimal current draw from the battery.

The MIC2291 is available with 2 levels of over-voltage

protection, 15V, and 34V. This allows designers to choose

the smallest possible external components with the appropri-

ate voltage ratings for their applications.

The MIC2291 is available in low-profile, Thin SOT23 5-lead

and 8-lead 2mm

×2mmMLF™packageoptions.TheMIC2291

has a junction temperature range of –40

°C to +125°C.

All support documentation can be found on Micrel’s web

site at www.micrel.com.

Typical Application

10

µH

0.22

µF

ceramic

0.95

Ω

95mV

1-Cell

Li Ion

3V to 4.2V

1

µF

2

3

1

4

5

MIC2291BD5

VIN

EN

SW

FB

GND

100mA

Thin SOT23 Flash LED Driver

Features

• 2.5V to 10V input voltage

• Output voltage up to 34V

• 1.2A switch current

• 1.2MHz PWM operation

• 95mV feedback voltage

• Overvoltage protection (OVP)

– Options for 15V and 34V

• Stable with ceramic capacitors

• <1% line and load regulation

• 1

µA shutdown current

• Over temperature protection

• UVLO

• Low-profile Thin SOT23-5 package option

• 2mm

× 2mm MLF™ package option

•–40

°C to +125°C junction temperature range

Applications

• Photo Flash LED driver

• Cell phones

• PDAs

• GPS systems

• Digital cameras

• IP phones

• LED flashlights

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

MLF and

PowerPAK is a trademark of Siliconix, Inc.

10

µH

0.22

µF

1

µF

1-Cell

Li Ion

3V to 4.2V

0.95

Ω

MIC2291-15BML

VIN

EN

SW

OVP

FB

GND

95mV

100mA

2mm

××××× 2mm Flash LED Driver with Output OVP