ZXLD1370_11 Datasheet, PDF (23/35 Pages) Diodes Incorporated – 60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER

Applications Information (Continued)
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Diodes Incorporated
ZXLD1370
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
1500.00
1250.00
1000.00
750.00
500.00
250.00
0.00
0
10%
9%
8%
7%
6%
5%
4%
3%
2%
1%
0%
10
20
30
40
50
60
70
80
90
100
PWM
PWM @ 1kHz
Error
Figure 27: 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
1500.00
10%
9%
1250.00
8%
7%
1000.00
6%
750.00
5%
4%
500.00
3%
250.00
2%
1%
0.00
0%
0
10
20
30
40
50
60
70
80
90
100
PWM
PWM @ 100Hz
Error
Figure 28: 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.
ZXLD1370
Document number: DS32165 Rev. 3 - 2
23 of 35
www.diodes.com
February 2011
© Diodes Incorporated