Application information, Zxld1370, A product line of diodes incorporated – Diodes ZXLD1370 User Manual
Page 27: Pwm output current control & dimming
ZXLD1370
Document number: DS32165 Rev. 5 - 2
27 of 39
September 2012
© Diodes Incorporated
ZXLD1370
A Product Line of
Diodes Incorporated
Application Information
(cont.)
PWM Output Current Control & Dimming
The ZXLD1370 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:
Buck mode - L=33uH - Rs = 150mΩ - 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
Figure 28 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:
Buck mode - L=33uH - Rs = 150mΩ - 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
cur
rent
[
m
A
]
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
E
rro
r
PWM @ 100Hz
Error
Figure 29 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. It can be driven also 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.