Al8805, Application information – Diodes AL8805 User Manual
Page 10
AL8805
Document number: DS35030 Rev. 4 - 2
10 of 16
July 2012
© Diodes Incorporated
AL8805
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
R
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.
0
100
200
300
400
500
600
700
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
PWM dimming [%]
LED
c
u
rr
ent
[
m
A
]
0
10
20
30
40
50
60
70
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
PWM dimming [%]
LED
cur
rent
[
m
A
]
µC
AL8805
GND
CTRL
µC
AL8805
GND
CTRL