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Mar29-06

SP6121 Buck/Boost Circuit for LED Driver up to 1.5A

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Sipex Corporation

SP6121 Buck/Boost Circuit for LED Driver up to 1.5A

Date: March 29, 2006

Brian Kennedy

Part Number: SP6121CN

Application Description: Provide high output current from 3Vin to 5Vin

Electrical Requirements:

Input Voltage

3.0V – 5.0V

Output Voltage

~3.9V (LED VF + 0.15V Vref)

Output Current

up to 1.5A

Circuit Description:

This circuit has been designed to provide 3Vin to 5Vin boost to White LEDs at

approximately 4V output at 1.5Amps. High efficiency and 3-5Volt input dictated

the choice of the controller and external components. In order to reduce the

reference voltage to a low 150mV and improve efficiency, an additional IC op

amp (LMV321) was used to amplify the reference to 1.2V feedback voltage. The

SP6121 is the synchronous buck controller that is being used as a buck/boost

DC/DC controller. A P-channel MOSFET and N-channel MOSFET are used for

higher efficiency in this synchronous SEPIC buck-boost configuration. The high

switching frequency (500 kHz) allows the use of small, mutually-coupled 4.7uH

inductors.

This report includes the application schematic complete with component part

numbers and figures 1-11 illustrating electrical performance of the design.

Design Solution 20

SP6121 Datasheet(PDF) 29 Page - Sipex Corporation