SP6682 Datasheet, PDF(5/12 Page) Sipex Corporation – High Efficiency Charge Pump Regulator for White LEDs

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SP6682 Datasheet, PDF (5/12 Pages) Sipex Corporation – High Efficiency Charge Pump Regulator for White LEDs

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PERFORMANCE CHARACTERISTICS: Continued

Refer to the typical application circuit, TAMB = 25Â°C, IO = 60mA unless otherwise specified.

2.7

3.3

3.6

3.9

4.2

Input Voltage (V)

4 LED's @ 30mA

4 LED's @ 15mA

Figure 7. Brightness vs. input voltage

100 Hz

500 Hz

Duty Cycle,%

Figure 8. Brightness vs duty cycle

100

General Overview

The SP6682 is a current regulated charge pump

ideal for converting a Li-Ion battery input for

driving white LEDs used in backlighting color

displays in cellular phones, PDAs, digital cam-

eras and MP3 players. The SP6682âs propri-

etary AutoBoost feature enables the IC to auto-

matically transition 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 oper-

ates with an internal 600kHz clock, enabling the

use of small external components. Other fea-

tures of SP6682 include PWM dimming control

as well as complete input/out disconnect in

shutdown. In shut down mode the IC draws less

than 1.5ÂµA 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 dia-

gram consists of four main blocks (Voltage

Reference, Mode Control, Clock Manager, Start-

up and Charge-Pump Switches) and two com-

OPERATION

parators (VMODE Comparator and VOUT Com-

parator).

1) Voltage Reference. This block provides the

306mV and 1.25V reference voltages needed

for the two comparators.

2) 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 selection outputs to the

X2 or X1.5 modes. VMODE 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. Dur-

ing start-up, until the reference is established,

this block keeps the charge pump inactive. Dur-

ing this period the output stays floating, 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 LED from experi-

Date: 5/5/04

SP6682 High Efficiency Charge Pump Regulator for White LEDs

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