Diodes AL8805 Manuel d'utilisateur télécharger pdf (Page 10)

AL8805

Document number: DS35030 Rev. 4 - 2

10 of 16

www.diodes.com

July 2012

L8805

Application Information (cont.)

PWM Dimming

LED current can be adjusted digitally, by applying a low frequency Pulse Width Modulated (PWM) logic signal to the CTRL pin to turn the device

on and off. This will produce an average output current proportional to the duty cycle of the control signal. In particular, a PWM signal with a

max resolution of 10bit can be applied to the CTRL pin to change the output current to a value below the nominal average value set by resistor

SET

. To achieve this resolution the PWM frequency has to be lower than 500Hz, however higher dimming frequencies can be used, at the

expense of dimming dynamic range and accuracy.

Typically, for a PWM frequency of 500Hz the accuracy is better than 1% for PWM ranging from 1% to 100%.

Figure 31 PWM Dimming at 500Hz

Figure 32 Low Duty Cycle PWM Dimming at 500Hz

The CTRL pin is designed to be driven by both 3.3V and 5V logic

levels directly from a logic output with either an open drain output

or push-pull output stage.

100

200

300

400

500

600

700

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

PWM dimming [%]

LED current [mA

]

0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10%

PWM dimming [%]

LED current [mA

]

µC AL8805

GND

CTRL

µC AL8805

GND

CTRL

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 16

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Diodes AL8805 Manuel d'utilisateur Page 10