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LMZ31710: Is the PGND/AGND Stackup within the PCB critical to the function of the part?

Jennifer London
Prodigy 10 points
Part Number: LMZ31710

The reference design for the LMZ31710 has the power arranged over a 4-layer PCB.  How critical are the dimensions between the 4 layers for the function of the regulator?  If critical, what are the stackup requirements for this regulator?

If I am building a 20 layer board rather than a 4 layer board, the capacitance created by the power, AGND and PGND planes can be quite different depending on where I put the layers.  Please help me understand the requirements of this chip.

  • 0
    TI__Mastermind 32400 points

    Hello Jennifer, 

    If the AGND has noise coupled to it from other noisy traces it will affect the performance of the device such as regulation, ripple ...etc. AGND pins are Zero volt reference for the analog control circuit. that important to keep it well isolated from noise traces and sources. 

    Going from 4 layers board to 20 layers board should not be an issue as long as the layout guideless are meet. More layers should help you to have better thermal and more option for signal traces. 

    For the AGND and PGND, make sure that they are separate from one another just it was done on the EVM. You can use that a reference. 

    Also you need to connect the pin23 and pin 2 connected externally. The AGND plan can be poured on the top layer of your board only to minimize any coupling and have the PGND just underneath it.

    It is important to have enough VIAS on the PGND to allow power flow thru the inner planes as this is used for current returns of the power stage of the device.  

    Thanks! 

    Tahar