SP6121CN-L Datasheet, PDF (29/42 Pages) Sipex Corporation – Low Voltage, Synchronous Step Down PWM Controller

Design Solution 20
SP6121 Buck/Boost Circuit for LED Driver up to 1.5A
Date: March 29, 2006
Designed by:
Brian Kennedy
Part Number: SP6121CN
Application Description: Provide high output current from 3Vin to 5Vin
Electrical Requirements:
Input Voltage
Output Voltage
Output Current
3.0V – 5.0V
~3.9V (LED VF + 0.15V Vref)
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.
Mar29-06
SP6121 Buck/Boost Circuit for LED Driver up to 1.5A
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Copyright ©2006
Sipex Corporation