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TPS23754EVM-383: Layout Design

Part Number: TPS23754EVM-383
Other Parts Discussed in Thread: TPS23754

TI evaluation board TPS23754EVM-383 is a 4 layer board with middle two layers for routing. Besides routing, its top and bottom layers are copper filled with split ground planes & doing SMT.

We are evaluating a 4 layer design but with different stacking. Middle two layers are split power & ground planes. Top and bottom layers are doing routing & SMT.

1) Is TPS23754EVM-383 layout stacking a MUST to bring up the TPS23754? Or it is more for EMI containment?

2) What do you think about the layout stacking like ours?

3) (Side question) If the power pad (VSS) is connected to RTN ground plane in accident, could this be the primarily reason to fail the detection? (The chip still has VSS pin 10 to return current to its source - the PoE side possibly?)

  • Hi David,

    Yes, the layout was designed with minimizing EMI in mind. I don't see an issue with using top and bottom for routing; however, you should still have respective ground planes on the primary and secondary for EMI. I recommend reading the app note below for more detailed layout technique design recommendations.

    www.ti.com/lit/an/slua469/slua469.pdf

    As for VSS, yes, the power pad should be connected to VSS as it would effect PSE/PD negotiation.
  • Hi,

    Thanks for the previous answers. Well done.

    On TPS23754EVM-383 board copper fills are go through underneath SMT devices (to name some of them: L2, L3, Q3, Q6, D7, D10, D21, C2, C16,  R14, R15). The capacitors and resistors are 0603 package.

    1) Why are you filling copper underneath SMT devices? In particular filling copper underneath capacitors and resistors of 0603 package?

    2) Could you possibly create assembly problem (or raise concern) filling copper underneath SMT devices?

    Thanks a lot.

    David

  • Hi David,

    I recommend consulting the PCB manufactures on what is the latest recommended connections for copper pours. I see no issues with using reliefs on these components if desired.

    Regards,

    Darwin