MIC2291

1.2A PWM Boost Regulator Photo Flash

LED Driver

PowerPAK is a trademark of Siliconix, Inc.

MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc.

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (

May 2007

1

M9999-051507

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

appropriate voltage ratings for their applications.

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

and 8-pin 2mm × 2mm MLF

MIC2291 has a junction temperature range of –40°C to

+125°C.

Data sheets and support documentation can be found on

Micrel’s web site at www.micrel.com.

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

• 1µA shutdown current

• Over temperature protection

• UVLO

• Low-profile Thin SOT23-5 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

Typical Application

10µH

0.22µF

ceramic

95mV

1-Cell

Li Ion

3V to 4.2V

1µF

2

3

1

4

5

MIC2291xD5

VIN

EN

SW

FB

GND

100mA

10µH

0.22µF

1µF

1-Cell

Li Ion

3V to 4.2V

MIC2291-15xML

VIN

EN

SW

OVP

FB

GND

95mV

100mA

Thin SOT23 Flash LED Driver

2mm x 2mm Flash LED Driver with Output OVP