SP6682EU 查看數據表（PDF） - Signal Processing Technologies

零件编号

产品描述 (功能)

比赛名单

SP6682EU

High Efficiency Charge Pump Regulator for White LEDs

Signal Processing Technologies 

APPLICATION INFORMATION: Continued

To 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.

VOUT 1

Anode

The guideline for divider resistor selections

is as follows: For high input voltage, the

SP6682 will work in X1.5 mode. When the

input voltage drops to the VTH threshold

voltage, it will switch to X2 mode automati-

cally. The VTH threshold voltage for mode

change can be calculated by:

SP6682

VFB

5

GND

8

R5

2.2uF

R6

2-wire W-LED

module

Cathode

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

source

The output voltage is set by the ratio of the

two resistors and the feedback control volt-

age as shown by:

VOUT

=

(

1

+

R5

R6

)

•

VFB

PROGRAMMING THE OPERATING MODE

VTH = (VF + 0.306 + M • ILED • ROUT)/1.5

Where VF and M are the forward voltage

and number of the white LEDs, ROUT is the

output resistance of the SP6682.

The equation for the voltage divider R1 and

R2 with VMODE = 1.25V is:

VTH = 1.25V • (1+R1/R2)

which can be expressed as R1:

R1 = (VTH / 1.25 -1) • R2

For the typical SP6682 application, Using

VF=3.6V, M=4, ILED=15mA, ROUT=16�, the

VTH will be 3.24V. Select R2=100k�, then

R1=158k�.

SP6682 can automatically change from X1.5

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.

VIN

3

VIN

R1

4

SP6682

VMODE

R2

C2

GND

8

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, smaller fly capacitors lead to larger

output resistance, thus decreasing the out-

Figure 14. Programming the Vmode Resistors

Date: 7/19/06 Rev D

SP6682 High Efficiency Charge Pump Regulator for White LEDs

7

© 2006 Sipex Corporation

Share Link: