SP6121CN-L Datasheet, PDF (21/42 Pages) Sipex Corporation – Low Voltage, Synchronous Step Down PWM Controller

Solved by
APPLICATION NOTE ANP13
TM
Applying the SP6121 as a SynchronousBuck-Boost 1.5A K2
LUXEON Driver
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.
Li Ion Battery
[3.4V – 4.3V]
High Efficiency
Buck/Boost
Converter w/
Output Current
Regulation
LUXEON® K2
1.5A Max [3.4 < VF > 4.0V]
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 by the SP6121 to regulate
properly.
Li Ion Battery
[3.4V – 4.3V]
SP6121 PWM
Controller
Boost / Buck
Cells
Over
Voltage
K2
Protection
Amplifier
Current
Sensing
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
Nov 28 06 AppNote: SP6121 as a Synchronous Buck-Boost LED Driver
Page 1
© 2006 Sipex Corporation