SP6687 Datasheet, PDF (5/12 Pages) Sipex Corporation – 4 Channel Charge Pump White LED Driver

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
modes. An external R_SET is used to set the current
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
enough for output capacitor C_OUT to reach a desired
voltage level. When the soft start turns off, the SP6687
will not sink current spiking from V_IN.
Mode Decision
The SP6687 uses a smart mode decision method to
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.
LED Current Setting
The current flowing through White LEDs connected
to the SP6687 can be set by R_SET. Every current that
flows through each respective White LED is 440
times greater than the current of R_SET. The white LED
current can be estimated by following equation:
THEORY OF OPERATION
where V_ISET =1.1V, and R_SET is the resistance con-
nected from I_SET to GND.
I_LED =440x
( ^VISET
R_SET
)
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
Li-ion
Battery
C_IN
1µF
R_SET
C1 1µF
C2 1µF
8
7
C1P
V_IN
1 _EN
2 _CTRL0
9
C1N
11
C2P
®
SP6687
10
C2N
V_OUT ⁶
LED1 ¹⁶
3 _CTRL1
LED2 ¹⁵
4 _CTRL2
LED3 ¹⁴
5 _ISET
GND
12
LED4 ¹³
C_OUT
1µF
Typical Application Circuit For 3-White LEDs
Date: 11/15/05
SP6687 4Channel Charge Pump White LED Driver
5
© Copyright 2005 Sipex Corporation