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TPS65219EVM: Noise during simultaneously work of buck1 and ldo1

Michael Grenader
Prodigy 130 points
Part Number: TPS65219EVM
Other Parts Discussed in Thread: TPS65219

Tool/software:

Hello

I'm using the TPS65219 in my project and face the following issue when im evaulating the ic using the evm:
During testing with a load applied to both Buck1 and LDO1 outputs simultaneously, I observed significant noise on the LDO1 output. This noise appears at the buck converter's switching frequency, and reaches 100mVpp when the modules are fully loaded. The issue only occurs when both outputs are loaded concurrently.
Has anyone else encountered this behavior, or have any suggestion for reducing this noise?

It happened on two evm boards

  • 0
    TI__Genius 10467 points

    Hello, 

    I can confirm that we are seeing this behavior on the EVM boards as well. This is a known issue we are working to improve. 
    The layout of the EVM has been found to impact this noise coupling behavior, and we are working on a revision to reduce this noise by further optimizing the layout. 

    For now, the suggested workaround would be to swap the usage of LDO1 and LDO2, since we are not observing any issues with LDO2. 

    Best Regards, 
    Sarah

  • 0 in reply to Sarah Lao
    Prodigy 130 points

    Hey, 

    Thank you for the quick response.

    Could you please point out the layout issue so I can avoid making the same mistake in my own project?

  • 0 in reply to Michael Grenader
    TI__Genius 10467 points

    Hi, 

    Our layout changes are still being tested, but with the following adjustments, we have noticed some improvements to the noise:

    • Isolating AGND from PGND
    • Adding more vias to the power pad of the PMIC
    • Added more stitching vias to GND planes

    These changes are yet to be finalized, and reduced the noise by a few mVpp.
    We're still investigating the root cause and fix. 

    So again, if you are looking to significantly reduce the risk of noise coupling, my recommendation would be to just swap the LDO usage.

    Best Regards,
    Sarah

  • 0 in reply to Sarah Lao
    Prodigy 130 points

    I see, thank you. 

    The problem with swapping LDO usage is that i need both ldo1 and ldo2 for powering sensitive rails that are below 1.2V (so i can't use ldo3/4).

    I will try to pay attention to what you mentioned and maybe just usr an external ldo instead of ldo1. 

  • 0 in reply to Michael Grenader
    TI__Genius 10467 points

    Understood. 
    Let me know if you have any further questions or concerns.

    Best Regards, 
    Sarah