Al8806, Application information – Diodes AL8806 User Manual
Page 8
AL8806
Document number: DS35144 Rev. 5 - 2
8 of 15
July 2013
© Diodes Incorporated
AL8806
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%.
0
100
200
300
400
500
600
700
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
PWM dimming [%]
L
E
D
c
u
rre
n
t [m
A
]
Figure 2 PWM Dimming at 500Hz
0
10
20
30
40
50
60
70
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
PWM dimming [%]
LE
D
cu
rr
e
nt
[
m
A
]
Figure 3 Low Duty Cycle PWM Dimming at 500Hz
The PWM 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.