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TSB41BA3F-EP: Separate Ground Planes for Analog/Digital Grounds

Parker Dodson
Guru 52172 points
Part Number: TSB41BA3F-EP

Tool/software:

Hi Team,

I am working with the TSB41BA3F-EP creating a board. 

The datasheet states that AVDD, PLLVDD-3.3, and DVDD-3.3V need to be tied together:

and there isn't really a reference in the datasheet I can find about the ground plane connection - the pinout table seems to imply that there should be a single ground plane on the board - but I want to confirm that is true. 

So with that - I have two questions:

1. Is it not recommended for this device to have separate analog and digital grounds for this device? 

2. Also to confirm - the digital and analog supplies do not need to be separate for this device? 

If separate grounds are not required or suggested and a single 3.3V power supply should be used for all 3.3V rails - why is this device able to do that, is there something special within the device or any reason why this wouldn't be suggested? I am a little new to this type of design and I was under the impression that analog and digital power should be separated for similar type devices - but what is presented in the datasheet is making me question that - so any help would be greatly appreciated here. 

Thanks!

Parker Dodson

  • 0
    Guru 316690 points

    High supply currents flow through both xVDD and xGND, so if you can route the grounds separately, it might be worthwhile to do this. (This is hard to do if you have a ground plane.)

    The supplies must be tied together somewhere, not necessarily near the chip. Typically, you'd have a star connection at the power supply so that the voltage drop over one supply trace is not visible to the other ones.

    If you use the same supply everywhere, then you do not have noise isolation. This probably matters for the PLL.