SP6687_06 Datasheet, PDF (2/4 Pages) Sipex Corporation – Evaluation Board Manual

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 I_LED = 440x (Voltage at I_SET /R5), where I_LED is required LED current, and Voltage at I_SET =
1.1V. R5 = 32 kΩ 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
CTRL2
0
0
0
0
1
1
1
1
Control Inputs
CTRL1
0
0
1
1
0
0
1
1
CTRL0
0
1
0
1
0
1
0
1
LED4
OFF
OFF
OFF
ON
OFF
OFF
ON
OFF
Output Status
LED3
LED2
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
OFF
ON
ON
ON
ON
ON
OFF
OFF
LED1
ON
OFF
OFF
OFF
ON
ON
ON
OFF
Dec18,2006 RevB
SP6687 Evaluation Board Manual
Page 2 of 4
© 2006 Sipex Corporation