5

Date: 7/1

9/06 Rev D

SP6682 High Efficiency Charge Pump Regulator for White LEDs

© 2006 Sipex Corporation

an input voltage to the mode comparator

which sets the logic state of the mode selec-

is compared to a 1.25V bandgap voltage.

For example, if one makes a 158K�/100K��

divider, the mode will change at 2.58 x 1.25

V = 3.23V. A comparator-based cycle-by-

cycle regulation ensures that no mode

change occurs during cycles.

3) Clock Manager. An internal 600 kHz

clock is generated in this block. Depending

on the mode control, the appropriate clock

phasing is generated here and sent to the

start-up and charge-pump switches block.

4) Start-up and Charge Pump Switches.

During start-up, until the reference is estab-

lished, this block keeps the charge pump

inactive. During this period the output stays

floating, and by consequence the charge

Charging of the output will occur (e.g. when

protecting the White LEDs from experienc-

ing high input voltages. Another important

operation of this block is the PWM/EN dim-

ming control, which is implemented in the

delay of each pump driver, so that the

enable high pulse width is proportional to

the delay of the individual pump switches.

A 306mV reference voltage is compared to

needed for the application. Output current is

set by a bias resistor from FB pin to GND pin

chosen by the relationship:

OPERATION

GENERAL OVERVIEW

The SP6682 is a current regulated charge

pump ideal for converting a Li-Ion battery

input for driving white LEDs used in back-

lighting color displays, Cell Phone Camera

Flash, PDAs, digital cameras and MP3 play-

ers. The SP6682ʼs proprietary AutoBoost

featureenablestheICtoautomaticallytrans-

itionfromX1.5boostmodetoX2boostmode

based on battery input voltage for optimal

efficiency and performance. The SP6682 is

able to efficiently drive up to six 20mA white

LEDs in parallel and maintain a constant

brightnessoveraverywideoperatingvoltage

range (2.7V to 5.5V). The SP6682 operates

with an internal 600kHz clock, enabling

the use of small external components.

Other features of SP6682 include PWM

dimmingcontrolaswellascompleteinput/out

disconnect in shutdown. In shutdown mode

the IC draws less than

1.5µA current. The output regulation is

achieved by sensing the voltage at the

feedback pin and modulating the switcher

between the charge pump and output

capacitor.

THEORY OF OPERATION

The SP6682 regulated charge pump block

diagram consists of four main blocks

(Voltage Reference, Mode Control, Clock

Manager, Start-up and Charge-Pump

1) Voltage Reference. This block provides

the 306mV and 1.25V reference voltages

needed for the two comparators.

2) Mode Control. An external voltage

di-