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  • Resolved

LMR14050-Q1 high ringing voltage at rising and falling edge

Hi,

 

Customer of mine intend to use LMR14050-Q1 (LMR14050SSQDDARQ1) in their car audio system however they’re seeing voltage overshoot and undershoot at rising and falling edge causing some interference with the radio frequencies

I’ve attached the material for your reference.

 

My questions are as below:

- the Rt value in customer schematic is 84K, thus calculated switching frequency is 308KHz. Would this cause the AM interference?

- Also, the value output capacitor is rather huge (3400uF). Would this cause the voltage overshoot/undershoot?

- Is there any way to reduce the ringing voltage effectively?

- could you help to review and comment the schematic and layout?

LMR14050-Q1 Interference issue.pdf

 

Thanks!

  • Hi

    I review the circuit and layout:

    1. Input bypassing design is bad, C601 is too small and voltage rating is not enough, pls change C601 to 0.22uF/50V parallel with 4.7uF/50V

    2. the snubber circuit R609 is 2.2ohm? C610 is 5600pF? pls try R609 4.7ohm and C610  1000pF/50V first.

    3. you may also add 4.7ohm in series with C602 to limit switching rising edge lsew rate. 

    4. Better to change the layout to improve input bypasing and heat shrink.

    B R

    Andy Chen

    andy.chen@ti.com 

  • In reply to Andy Chen:

    Also I can add that the electrolytic capacitor C633 probably needs to be on the other side of L604 to damp out ringing. The layout will probably need to be completely re-done.

    Best  Regards,

    John Tucker

    BSR-CCP LV/MV DC/DC Applications

  • In reply to Andy Chen:

    Hi Andy,

    Thanks for the recommendation.
    Could you further elaborate and teach me how to improve the customer's layout?
    Thanks
  • In reply to Eng Lih Khaw:

    Hi Eng,

    What's your email add? I will send you layout suggestion by email later as it's not convenient to send attachment here.

    B R
    Andy
  • In reply to Andy Chen:

    Hi Andy,

    Pardon me for delay.

    Could you send it to eng-k@macnica.com ?

    Thank you for your support!

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