Diodes ZXLD1374 - Manual (Page 30)

ZXLD1374
Document number: DS35032 Rev. 3 - 2
30 of 39
www.diodes.com
September 2012
© Diodes Incorporated
ZXLD1374
A Product Line of
Diodes Incorporated
Application Information
(cont.)
PWM Output Current Control & Dimming
The ZXLD1374 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with 1000:1 resolution;
however higher dimming frequencies can be used – at the expense of dimming dynamic range and accuracy.
Typically, for a PWM frequency of 1kHz, the error on the current linearity is lower than 5%; in particular the accuracy is better than 1% for PWM
from 5% to 100%. This is shown in the graph below for Buck mode:
Normalized LED
Current Error
I
LED
0.0%
2.5%
5.0%
7.5%
10.0%
12.5%
15.0%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
PWM duty cycle
N
ormali
zed LED c
urren
t error
0
250
500
750
1000
1250
1500
LED c
urren
t (mA)
V
IN
= 24V
T
A
= 25°C
f
PWM
= 1kHz
Figure 37 LED Current Linearity and Accuracy with PWM Dimming at 1kHz
For a PWM frequency of 100Hz, the error on the current linearity is lower than 2.5%; it becomes negligible for PWM greater than 5%. This is
shown in the graph below:
Normalized LED
Current Error
I
LED
0.0%
2.5%
5.0%
7.5%
10.0%
12.5%
15.0%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
PWM duty cycle
Normali
zed LE
D curr
en
t err
or
0
250
500
750
1000
1250
1500
LE
D current
(mA)
V
IN
= 24V
T
A
= 25°C
f
PWM
= 100Hz
Figure 38 LED Current Linearity and Accuracy with PWM Dimming at 100Hz