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TPS923653: Issues with TPS923653 LED Driver: Audible Noise and Excessive Ringing with PWM Dimming

Craig Peckett
Prodigy 110 points
Part Number: TPS923653

Tool/software:

Dear Texas Instruments Support Team,

I am currently working on a project that uses the TPS923653 LED driver as a boost converter to power an LED panel. The circuit works well when the EN/PWM and ADIM pins are both high, allowing the LED panel to be fully on. However, I encounter significant issues when introducing a PWM signal at the EN/PWM pin for dimming.

Specifically, I am experiencing:

  1. A loud audible noise coming from the circuit.
  2. Excessive ringing at the switching node.

To mitigate these issues, I have attempted the following:

  • Increased the PWM signal frequency from 1 kHz to 20 kHz. While this reduced the audible noise for the majority of the time, it did not completely eliminate it at lower duty cycles. Additionally, the switching node still exhibits significant ringing, which does not appear normal.

Could you please provide guidance on the following:

  1. Is it normal to experience loud audible noise and excessive ringing when using PWM dimming with the TPS923653?
  2. Are there specific component values or configurations recommended to minimize these issues?
  3. What additional steps can I take to ensure a stable and noise-free operation when using PWM dimming?

Thank you for your assistance.

Craig

  • 0
    TI__Mastermind 23150 points

    Hi Craig,

    Several points to check:

    • Please send me a clearer schematic. The above one is hard to read.
    • Also, do you have any oscilloscope captures illustrating the excessive ringing? 
    • Please provide the spec of your input voltage, LED voltage and LED current (I-V curve of the LED is preferred).
    • What is the dimming mode you are using?
    • Do you have any idea where the audible noise comes from? Inductor? Output capacitor?

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Prodigy 110 points

    Hi Steven,

    • Here is a link to a folder with the schematics and a picture of the oscillation. Schematic and scope capture
    • A lot of the details are in the schematic but, input voltage 12-24V, LED voltage is 35V and LED current is set to 333mA.
    • I am attempting to use PWM dimming.
    • I think the audible noise is coming from the inductor but it is hard to tell.
    • I increased the output capacitance to 100uF and then increased the inductor to 680uH and the audible noise seemed to improve but the oscillation is still on the switching node.

    Thanks


    Craig

  • 0 in reply to Craig Peckett
    TI__Mastermind 23150 points

    Hi Craig,

    Sorry but I cannot access the files you posted. Could you send them to me through e-mail? I have sent you my e-mail address through private message on this E2E forum. Thanks.

    Best Regards,

    Steven