SP6121 datasheet(21/42 Pages) SIPEX

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Nov 28 06 AppNote: SP6121 as a Synchronous Buck-Boost LED Driver

Page 1

Introduction

The SP6121 is a 500kHz PWM controller with input voltage range from 3.0V to

5.5V. This is ideal for drawing power out of a one-cell Li Ion battery which varies

from 3.4V to 4.3V. The requirement for this application is to provide a maximum

1.5A regulated current into a K2 Lumileds LUXEON® LED.

The topology used here is a “non-inverting Cuk boost/buck”. The circuit will also

use an external amplifier for converting the current sensing (ILED) into the

appropriate

voltage

level

requested

the

SP6121

regulate

properly.

Principle of Operation

The simplified form of a boost buck converter is shown below. The converter can

be separated into two cells, a boost cell made out of S1 and L1 and a buck cell

around S2 and L2. S1 and S2 are controlled out of phase. Phase 1 is S1 closed

Li Ion Battery

[3.4V – 4.3V]

LUXEON® K2

1.5A Max [3.4 < VF > 4.0V]

High Efficiency

Buck/Boost

Converter w/

Output Current

Regulation

Li Ion Battery

[3.4V – 4.3V]

SP6121 PWM

Controller

Current

Sensing

Amplifier

Boost / Buck

Cells

Over

Voltage

Protection

Solved by

APPLICATION NOTE ANP13

Applying the SP6121 as a SynchronousBuck-Boost 1.5A K2

LUXEON Driver

SP6121 Fiches technique(PDF) 21 Page - Sipex Corporation

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