9
Date: 3/31/06 RevG SP6683 1X/1.5X Charge Pump LED Driver for Flash or Backlight © Copyright 2006 Sipex Corporation
The SP6683-03ER has the discharge MOSFET
disabled ensuring that the output node is at high
impedance during shutdown. This can be useful
if the system is feeding LED current from an-
other source while the SP6683 is in shutdown.
The SP6683-LV offers a lower reference volt-
age that allows to reduce efficiency loss occur-
ring in the current sense resistor. This part is
ideal for driving single LEDs for Flash applica-
tions.
Reducing Component Count
It is possible to reduce the number of external
components by shorting pins 2 & 9 and omitting
the flying capacitor. In this mode, the charge
pump operates in a "quasi" doubler mode. This
reduces efficiency but does allow for one less
external capacitor. This circuit is recommended
only when Input and Output Voltages have
similar range, which is very common when
driving white LEDs from a Li-Io battery.
Flying Cap Removed
In this application, the bias resistor can be se-
lected by:
R
B
=
VFB
I
LED (TOTAL)
where I
LED(TOTAL)
is the total operating current
of all the white LEDs.
To use SP6683 as a voltage source for fixed
voltage applications, a voltage divider is need to
program the output voltage, as shown in the figure
above. The output voltage is set by the ratio of
the two resistors and the feedback control volt-
age as shown by:
V
OUT
= ( 1 +
R5
) • V
FB
R6
Brightness Control Using PWM
Dimming control can be achieved by applying a
PWM control signal to the EN/PWM pin. The
brightness of the white LEDs is controlled by
increasing and decreasing the duty cycle of the
PWM signal. While operating frequency range
is from 60Hz to 700Hz, the recommended maxi-
mum brightness frequency range is from 60Hz
to 200Hz. A repetition rate of at least 60Hz is
required to prevent flicker.
Three Options for Optimization
The SP6683 family includes three options that
allow the user to optimize the LED driving
circuit. The SP6683 includes an on-board dis-
charge switch that ensures that V
OUT
is com-
pletely discharged in shutdown. This feature is
very useful in systems using PWM dimming,
when the SP6683 is periodically turned on and
off. The discharge switch ensures that the fall-
ing and rising edges of the LED current have
similar durations.
APPLICATION INFORMATION
SP6683
1 Vout
C1P
2
Vin3
Vmode
4
FB
5
10
C2P
C1N
9
GND
8
C2N
7
EN/PWM
6
EN/PWM
C1
2.2uF
6.3V/0603
C4
6.3V/0603
C3
1uF
6.3V/0603
LED1
Rb
1.5 Ω
1% / 0603
Vin
2.7V~4.2V
Io=Vfb/Rb
2.2uF
