SP6682 Datasheet, PDF(6/13 Page) Sipex Corporation – High Efficiency Charge Pump Regulator for White LEDs

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SP6682 Datasheet, PDF (6/13 Pages) Sipex Corporation – High Efficiency Charge Pump Regulator for White LEDs

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SP6682

High Efficiency White LED Charge Pump Regulator

THEORY OF OPERATION

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 players.

The SP6682âs proprietary AutoBoost feature

enables the IC to automatically trans-ition

from X1.5 boost mode to X2 boost mode

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

brightness over a very wide operating voltage

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 dimming

control as well as complete input/out

disconnect in shutdown. In shutdown mode

the IC draws less than 1.5Î¼A 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.

OPERATION

The SP6682 regulated charge pump block

diagram consists of four main blocks (Voltage

Reference, Mode Control, Clock Manager,

Start-up and Charge-Pump Switches) and two

comparators (VMODE Comparator and VOUT

Comparator).

Voltage Reference.

This block provides the 306mV and 1.25V

reference voltages needed for the two

comparators.

Mode Control

An external voltage divider connected to the

VMODE pin will define an input voltage to the

mode comparator which sets the logic state of

the mode selec-tion outputs to the x2 or x1.5

modes. VMODE is compared to a 1.25V bandgap

voltage. For example, if one makes a

158Kâ¦/100Kâ¦ 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.

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.

Start-up and Charge Pump Switches

During start-up, until the reference is

established, this block keeps the charge pump

inactive. During this period the output stays

floating, and by consequence the charge pump

drivers are now referenced to VOUT.Charging

of the output will occur (e.g. when VIN is

ramped up to 4.2V, VOUT ramps only up to

about 3V), but not to the value of

VIN,protecting the White LEDs from

experiencing 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.

VOUT Comparator and Output Control

A 306mV reference voltage is compared to

feedback output voltage to control the

VOUTneeded for the application. Output

current is set by a bias resistor from FB pin to

GND pin chosen by the relationship:

I OUT

VFB

RFB

where VFB = 306mV.

CONFIGURING THE SP6682 AS VOLTAGE

OR CURRENT SOURCE

The white LED load configuration used by

customers can be discrete white LEDs or a

white LED module. Inside the white LED

module, there may or may not be resistors in

series with the white LEDs. According to the

different application requirements, the SP6682

can be configured as either a voltage source or

a current source to provide solutions for these

6/13

Rev. 2.0.0

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