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TPS65131: TPS65131 reduce noise...

Andre Strul
Expert 1330 points
Part Number: TPS65131

hi to all and thank you for taking the time to assist us in our design.

We want to reduce the noise of this convertor to very low levels. After reading your own papers we decided to place some RC snubbers.
On positive side , we placed a RC snubber across INP and OUTP . We tested . Some oscillations and noise are reduced. However the main SW mosfet is between INP and GND. Can we place a RC snubber between INP and GDN ? (220pf/10R)
Second on the negative side (on the block diagram from the datasheet) we only see one SW mosfet . So we assume we can place a RC snubber between INN and OUTN . However the second mosfet is not present. Can we also place a RC snubber between INN and GDN ?

waiting for your reply.

thank you in advance.

Andre

  • 0
    Expert 1330 points
    *** correction ***
    on the negative side the question is can we place a RC snubber between VNEG and GDN (as well as INN and OUTN)
  • 0 in reply to Andre Strul
    TI__Expert 8010 points
    Hello Andre,

    Sure you can use a RC snubber connected between the switching node and GND, actually that is the common way to easily reduce the noise (be aware of the losses), as for the boost as well as for the inverting buck-boost.
    I have a question, why would you want to use two RC-networks on each converter? Please check if you can damp the noise level by connecting the RC filter on the switching nodes and let me know if this is enough for your requirements.
    BTW here is a good blog to dimension the RC filter:
    e2e.ti.com/.../calculate-an-r-c-snubber-in-seven-steps

    Best Regards.
    Ilona
  • 0 in reply to Ilona
    Expert 1330 points
    hi Ilina and thanks for the reply.
    We are using this IC on a audio application , so very low noise is very important . Our question was not asnwerd , on positive side should we use INP to GDN or VPOS to GDN? Also on negative side , we have no idea what we should connect to GDN..we think that RC snubber shoud be betwen INN to OUTN ?

    thanks
    Andre
  • 0 in reply to Andre Strul
    TI__Guru 65340 points
    Hello Andre,

    For damping the noise you need to add an RC snubber from the switch node to GND at any converter. The switch nodes of TPS65131 are
    boost: INP
    inverting buck-boost: OUTN

    So if you want to use an RC snubber on each converter, use one from INP to GND on the positive converter and one from OUTN to GND on the negative converter.

    Please check as well the app note in the above post because this is giving you the right calculation method for the snubber.

    BTW, another method to reduce noise on converters is the use of a high frequency capacitor on the output. The advantage of this method is that there is no power dissipation like in an RC snubber.

    Please be aware that both methods need an extremely good layout to be effective.

    Best regards,
    Brigitte