SP6687 datasheet(2/4 Pages) SIPEX

2 / 4 page

Dec18,2006 RevB

SP6687 Evaluation Board Manual

Page 2 of 4

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 a 3 mode charge pump: x1, x1.5, and x2. An external resistor R5 is used to set the current of

the white LEDs. SP6687 has an input current regulation to reduce the input ripple. Users can control

white LED on/off via three programming bits: CTRL0, CTRL1 and CTRL2. When an external PWM signal

is connected to the control pin, the brightness of white LEDs is adjusted by the duty cycle. Each channel

can support up to 30mA of current. A current limiting circuit is also included in the SP6687 for short

circuit protection. Whenever the output sources a dangerously high current, the current limiting circuit

takes over the output regulation circuit and reduces the output current to an acceptable level. This device

is available in a 4mm x 4mm, 16 pin QFN package.

Capacitor C1 is a decoupling capacitor. Resistors R1 – R4 are used to pull down inputs if they are left

floating. Capacitors C2 – C4 are used by the charge pump.

USING THE EVALUATION BOARD

1) Powering Up the SP6687 Circuit

The SP6687 Evaluation Board can be powered from a 4.5V power supply or from 3 alkaline cells.

Connect 4.5V source pin with short lead directly to the “Vin” and -4.5V /GND pin to the “GND” posts.

2) Selecting the Bias Resistor

LED current can be adjusted up to 30mA per string with an external resistor R5. The R5 value may be

determined as ILED = 440x (Voltage at ISET /R5), where ILED is required LED current, and Voltage at ISET =

1.1V.

R5 = 32 k

is installed.

3) Selecting the number of illuminated LEDs

The number of illuminated LEDs can be selected using CTRL0 – CTRL2 programming bits (see Table 1).

Table 1. Programming Table

Control Inputs

Output Status

CTRL2

CTRL1

CTRL0

LED4

LED3

LED2

LED1

OFF

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