7

Date: 7/1

9/06 Rev D

SP6682 High Efficiency Charge Pump Regulator for White LEDs

© 2006 Sipex Corporation

Anode

5

8

SP6682

Cathode

R6

1

R5

2.2uF

2-wire W-LED

module

GND

Figure 13. Driving 2-wire white LED module as voltage

source

C2

GND

4

R1

SP6682

8

R2

3

Figure 14. Programming the Vmode Resistors

The output voltage is set by the ratio of the

two resistors and the feedback control volt-

age as shown by:

PROGRAMMING THE OPERATING MODE

SP6682canautomaticallychangefromX1.5

mode to X2 mode for highest efficiency. To

use this feature, divider resistors should be

chosen according to the specific applica-

tion, as shown in Figure 14.

The guideline for divider resistor selections

is as follows: For high input voltage, the

SP6682 will work in X1.5 mode. When the

voltage, it will switch to X2 mode automati-

change can be calculated by:

output resistance of the SP6682.

which can be expressed as R1:

For the typical SP6682 application, Using

CAPACITOR SELECTION

Ceramic capacitors are recommended for

their inherently low ESR, which will help

produce low peak to peak output ripple, and

reduce high frequency spikes.

The fly capacitor controls the strength of the

charge pump. Selection of the fly capacitor

is a trade-off between the output voltage

ripple and the output current capability.

Decreasing the fly capacitor will reduce the

output voltage ripple because less charge

will be delivered to the output capacitor.

However,smallerflycapacitorsleadtolarger

output resistance, thus decreasing the out-

T

o use the SP6682 as a voltage source for

fixed voltage applications, a voltage divider is

needed to program the ouput voltage, as

shown in Figure 13.

APPLICATION INFORMATION: Continued