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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:

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:

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-

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

Vin

3

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