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Date: 11/15/05

SP6687 4Channel Charge Pump White LED Driver

© Copyright 2005 Sipex Corporation

THEORY OF OPERATION

The SP6687 is a high efficiency charge pump white

LED driver. It provides 4 channels of low drop-out

voltage current source to regulate the current for 4

white LEDs.

For high efficiency, the SP6687

implements 3 modes of charge pump: x1/x1.5/x2

level of the White LEDs. SP6687 has an input current

regulation circuit to reduce the input ripple.

Soft Start

The SP6687 includes a soft start circuit to limit the

inrush current at power on and mode switching. The

soft start circuit holds the input current level long

Mode Decision

select the working mode for maximum efficiency. The

mode decision circuit senses the output and LED

voltage for up/down selection.

Dimming Control

CTRL0, CTRL1 and CTRL2 are used to control the

on/off of correlated White LEDs. When an external

PWM signal is connected to the control pin, the

brightness of the white LEDs is adjusted by the duty

cycle.

The current flowing through White LEDs connected

flows through each respective White LED is 440

current can be estimated by following equation:

LED Current Setting

Thermal Shutdown

The SP6687 provides a high current capability to drive

4 white LEDs. A thermal shutdown circuit is needed to

protect the chip from thermal damage. When the chip

reaches the shutdown temperature of 150ºC, the

thermal shutdown circuit turns off the chip to prevent

thermal accumulation in the chip.

Overvoltage Protection

SP6687 regulates the output voltage by controlling

the input current. When the output voltage reaches the

designated level, SP6687 reduces the input current.

Subsequently, the output voltage regulation also serves

as an overvoltage protection circuit.

Short Circuit Protection

A current limiting circuit is also included in the SP6687

for short circuit protection. Whenever the output

sources a dangerously high current, the current limit-

ing circuit takes over the output regulation circuit and

reduces the output current to an acceptable level.

APPLICATION INFORMATION

Typical Application Circuit For 3-White LEDs

EN

CTRL0

CTRL1

CTRL2

C1P

C1N

C2P

C2N

GND

LED1

LED2

LED3

LED4

C1 1µF

C2 1µF

1

3

4

5

6

7

89

10

11

12

13

14

15

16

2

Li-ion

Battery

SP6687

1µF

1µF

®