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TPS922052: Using multiple regulators on same power supply causes one regulator to flicker.

Sam Lane
Prodigy 30 points
Part Number: TPS922052

Tool/software:

I recently designed a circuit based around the TPS922052, built for dimming a set of LEDs in series (Vf = 36V) from an input voltage of 42V and a 3.3V PWM signal (running in hybrid dimming mode). Please see below images for schematic and PCB layout.

The system dims the LEDs well, with excellent low-level performance. However, if I take two of these circuits, connect them both to the same power supply (a 42V Meanwell HLG PSU capable of providing 5A), then one of the two LED strings (supplied by the TPS922052) will flicker. I have built over 30 of these PCBs and the issue is present with all boards, but only one ever flickers at a time (and it is not consistent which one will flicker).

The PWM signals for each regulator are each from separate GPIO pins on the microcontroller. 

The input voltage remains steady, with <200mV peak to peak variation under load (including during the output flicker).

If you have any suggestions as to what could be causing this interaction to occur, I would be very grateful. I am happy to take any measurements that would aid this investigation!



  • 0
    TI__Genius 9255 points

    Hi Sam,

    Our expert is in public holiday and reply will be delayed to 5/6

    Thanks for your understood.

    BR

    Monet Xu

  • 0 in reply to Monet Xu
    TI__Mastermind 30431 points

    Dear Sam,

    Thanks for reaching out! In theory, you will not see flicker even that you are using the same power supply for two LED drivers.

    Firstly, I would like to double confirm with you about the configuration. So, you have one power supply, and it will supply two LED drivers, each LED driver will be connected with a separate LED string.

    I would recommend that you can first check whether the current limit of the input power supply is triggered.

    And what is the configuration of ADIM and PDIM? Like PWM frequency and duty? I would recommend you can test the current waveform of the LED string or the current waveform of the inductor to compare what's the difference between two LED driver. If you can see flicker, I believe it will also show some difference from the waveform.

    Thank you!

    BRs

    Lucia