Mp24881- LED Flicker Observed during the Hybrid Dimming

DC-DC Power Converters
1

Hello everyone,

I’m using the MP24881 evaluation board to test a COB LED and check its deep-dimming performance.

My setup is:

  • Input voltage: 48 VDC

  • LED: 37 Vf, 350 mA COB

  • ADIM frequency: 10 kHz

  • PWM source: AWG

I’m following the hybrid-dimming method described in the datasheet. The plan is to keep the ADIM duty constant and vary the PWM duty for deeper dimming.

First, I kept the PWM pin HIGH and varied the ADIM duty at 10 kHz. The LED output was stable down to approximately 3% ADIM duty. Below 3%, I started seeing visible stutter or flicker.

After that, I kept the ADIM duty fixed at 3% and varied the PWM duty to achieve deep dimming. However, I observed flicker at most brightness levels, not only at the lowest brightness settings.

I also tried changing the inductor value to both higher and lower values, but this did not improve the flicker.

Has anyone experienced similar behavior with the MP24881? What parameters or components should I check first to achieve stable hybrid deep dimming?

I would especially appreciate advice on the following:

  1. Recommended ADIM and PWM frequency and duty-cycle settings for deep dimming.

  2. Whether operating at 3% ADIM is too close to the practical limit.

  3. Recommended PWM frequency for hybrid dimming.

  4. Whether COUT, compensation, or any other external components could be causing this issue.

  5. Which oscilloscope waveforms or measurements would be useful for identifying the cause.

My target is smooth, flicker-free deep dimming down to approximately 0.1%.

Thanks in advance for your suggestions.