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Analog domain capacitors in TPS799

Yaroslav Mudritsky
Intellectual 760 points
Other Parts Discussed in Thread: TPS799

Hi all,

In NR pin of TPS799 (fixed voltage) which need a 0.01uF bypass capacitor, in analog applications that need to have Analog and Digital ground separated, should I connect this capacitor to Analog or Digital ground?

  • 0
    TI__Expert 6825 points
    Hi Yaroslav,

    It is going to depend on which ground plane the ground pin of the device is on, if only one of the ground planes is connected to the ground pin this is the ground plane the NR cap will go on. If the ground planes meet at the ground pin then the NR cap should be placed on the quieter of the ground planes as close to the ground and NR pin as possible.

    Best Regards,
    Mark
  • 0 in reply to Mark Sellers
    Intellectual 760 points

    Thank you. I want to ask also about decoupling capacitors. See this for example:

  • 0 in reply to Yaroslav Mudritsky
    TI__Guru 55940 points
    Hi Yaroslave,

    TPS799 does not require an input capacitor; however, it is good analog design practice to connect a local low ESR capacitor close to the input pin. This capacitor should be grounded to the same ground as the LDO.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Intellectual 760 points

    Thanks for your answer. About connection of Analog plane to Common ground plane I've found that it's highly adviced to use a single connection point. It's ever better, as someone say or as adviced in some application notes, to connect Analog plane through a FB to Common plane. In case of lackage of information about specifics of this FB or in general case about separating Digital and Analog ground, how do you advice to choose this FB specifics? Or there's a common value used in specific applications? (like: Digital between 10-50Mhz or 100-500Mhz ecc.)

  • 0 in reply to Yaroslav Mudritsky
    TI__Guru 55940 points
    Hi Yaroslave,

    We recommend that all components relating to the LDO be terminated to the same ground as the LDO's GND pin(s). If multiple ground planes are used, we recommend that these planes meet at the GND pin of the LDO. This allows the LDO to operate with a common reference at the GND pin.

    Very Respectfully,
    Ryan