SS6896 datasheet(10/12 Pages) SSC

10 / 12 page

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10 of 12

Rev.2.01 6/06/2003

SS6896

DC voltage is shown in Fig. 22. As the DC voltage

increases, the voltage drop on R2 increases and the

voltage drop on R1 decreases.

Thus, the LED current decreases. The selection of

R2 and R3 should make the current from the

variable DC source much smaller than the LED

current and much larger than the FB pin bias current.

For VDC range from 0V to 5V, the selection of

resistors in Fig. 22 gives dimming control of LED

current from 20mA to 0mA.

3. Using a Filtered PWM Signal

The filtered PWM signal can be considered as an

adjustable DC voltage. It can be used to replace the

variable DC voltage source in dimming control. The

circuit is shown in Fig. 23.

ZD1

19.6V~20.4V

BZV55-B20

1K£[

GND

SHDN

10µH

0.033µF

4.7µF

OFF

3V to 4.2V

VIN

CH521S-30

62£[

1µF

IOUT=ILED=20mA

Fig. 20 White LED driver with open-circuit protection

GND

SHDN

SS6896

0.033

µF

62£[

1K£[

PWM

ZD1

GND

SHDN

SS6896

0.033

µF

Ω

PWM

ZD1

3.3K

Ω

OFF

(a)

(b)

Fig. 21 Dimming-control using a PWM signal

SS6896

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