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TPS65261-1: Grounding

Ashutosh Nahar
Intellectual 640 points
Part Number: TPS65261-1
Other Parts Discussed in Thread: TPS65261, TPS7A8300

HI,

I am using two different ground for  TPS65261 analog and digital.

What should be the ground technique to separate the two ground? 

Current i am using FBMJ1608HM180NTR ferrite bead between two ground.

How much should be the value  of resistance of ferrite bead ?

I am using TPS7A8300 LDO what type of grounding i need to use analog or digital ground for this in my board ?

Thanks
Ashutosh

  • 0
    TI__Mastermind 18510 points

    Hi

    I think the digital ground you said should be the power ground(PGND).
    I suggest you to refer to fig70 layout example in datasheet or EVM layout to do at first, seperate Analog gnd with PGND at the top layer, and Analog gnd is connected to thermal pad gnd individually at the top, both GND are connected at the bottom by some vias as well.
    and if you would like to do single connection between AGND and PGND by 0ohm resistor, I recommend 0805 size at least.

    By the way, please post another topic for TPS7A8300, so that some guy can get it and answer to you.
     
    BR,
    Yuchang

  • 0 in reply to Yuchang Zhang
    Intellectual 640 points
    HI Yuchang,

    Thanks for your reply.

    Yes, when i am saying digital ground, it mean that PGND.
    I have a few more queries:-

    1. The thermal pad should need to connect to analog gnd or DGND ?
    in fig 70 of datasheet I can see that it is getting connected to AGND and PGND both.
    I think it should be AGND, Please confirm once ?

    2. If i use ferrite bead technique then is it good option or not? I am using FBMJ1608HM180NTR this part for separate between two gnd.
    Is it ok ?

    Thanks
    Ashu
  • 0 in reply to Ashutosh Nahar
    TI__Mastermind 18510 points
    Hi,
    1. The thermal pad should need to connect to analog gnd or DGND ?
    in fig 70 of datasheet I can see that it is getting connected to AGND and PGND both.
    I think it should be AGND, Please confirm once ?
    ---Generally, it is the chip sub-GND and PGND as well,
    and we make AGND signle-connected to it. not make AGND and PGnd together with a large plane just in case power high-frequency noise easily coupled to analog signal.

    2. If i use ferrite bead technique then is it good option or not? I am using FBMJ1608HM180NTR this part for separate between two gnd.
    Is it ok ?
    ---Acutually, as my personal experience, it's Ok, and mostly for cost-down, use 0 OHM instead. but sorry we have no such experience on this part.

    BR,
    Yuchang