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TPS92692-Q1: There is a visible abnormal noise on the PCBA

Hope Chen
Expert 1030 points
Part Number: TPS92692-Q1

would you help check the SCH and give some advices about the below isue

1,Spec: INPUT：6-24V ;OUTPUT:18-26V/1A（7S*LED）

2, Question: There is a visible abnormal noise on the PCBA when PWM dimming input with the duty is 8%( Current: 80ma)，The frequency of PWN is about 200hz. After testing, we had eliminated the problem of inductive abnormality, and we had tried to remove the coupling ceramic capacitance directly from the output terminal and inductance. The visible abnormal noise  is still there. 

3, SCH is as below.

  • 0
    TI__Mastermind 25500 points

    Hello Hope,

    I can't read that schematic even if I zoom in. Do you have a more clear one? Also, can you take scope shots of the LED current and FET drain voltage when this is happening? Is it audible noise, LEDs flickering, or both?

    Thanks,

    Clint

  • 0 in reply to Clinton Jensen
    Expert 1030 points

    sorry for my mistake

    it's audible noise, and led work is normal

    CE16 DRL&PO LED SCH 20180409.pdf

  • 0 in reply to Hope Chen
    TI__Mastermind 25500 points

    Hello Hope,

    Thanks, I got some other information too and it looks like it is operating fine, there is just audible noise. This is common and is always the ceramic capacitors and/or the inductor. It sounds like you have done some work regarding the inductor, but I still wouldn't rule it out yet.

    I would start by replacing the input capacitors with aluminum electrolytic caps to see if that makes a difference. If not then the output capacitors. If not you may even need to try the sepic capacitor. Any ceramics can buzz so you need to figure out which ones are. If it isn't any of them then the inductor needs to be looked at more closely. If it is any of the ceramics then you will likely just need to experiment with different case sizes, numbers (splitting the current between more of them usually), or amount of capacitance. Unfortunately audible noise requires some experimentation, but it can be mitigated.

    Regards,

    Clint