Zxld1371, Applications information, A product line of diodes incorporated – Diodes ZXLD1371 User Manual
Page 33: Cont.), Pwm output current control & dimming
ZXLD1371
ZXLD1371
Document number: DS35436 Rev. 1 - 2
33 of 42
February 2012
© Diodes Incorporated
A Product Line of
Diodes Incorporated
Applications Information
(cont.)
PWM Output Current Control & Dimming
The ZXLD1371 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with
up to 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:
Figure 10. 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:
Figure 11. LED Current Linearity and Accuracy with PWM Dimming at 100Hz
The PWM pin is designed to be driven by both 3.3V and 5V logic levels and as such doesn’t require open collector/drain
drive. It can also be driven by an open drain/collector transistor. In this case the designer can either use the internal pull-up
network or an external pull-up network in order to speed-up PWM transitions, as shown in the Boost/ Buck-Boost section.
Buck mode - L=33uH - Rs = 150m
Ω - PWM @ 1kHz
0.00
250.00
500.00
750.00
1000.00
1250.00
1500.00
0
10
20
30
40
50
60
70
80
90
100
PWM
L
E
D
cu
rr
en
t [
m
A
]
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
E
rro
r
PWM @ 1kHz
Error
Buck mode - L=33uH - Rs = 150m
Ω - PWM @ 100Hz
0.00
250.00
500.00
750.00
1000.00
1250.00
1500.00
0
10
20
30
40
50
60
70
80
90
100
PWM
L
E
D c
u
rr
e
n
t [
m
A]
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
E
rro
r
PWM @ 100Hz
Error