ZXLD1370

ZXLD1370

Document number: DS32165 Rev. 2 - 2

22 of 33

www.diodes.com

May 2010

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Buck mode - L=33uH - Rs = 150m

Ω - PWM @1kHz

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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 = 150m

Ω - PWM @100Hz

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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.

Figure 29: PWM dimming from open collector switch

Figure 30: PWM dimming from MCU