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TMS320F28P650DK: Can Pin E12 (VSSOSC) Be floating?

Mike Allette
Intellectual 355 points

Part Number: TMS320F28P650DK

Hi,

 

I routed a board using a F28P650DK9NMR package. I accidentally tied the E12 (VSSOSC) pin to 3.3V.

If I isolate that pin from the board layout, is it ok for it to be floating? Is this pin internally tied to GND?

Also, I'm not using an external oscillator.

 

  • 0
    TI__Mastermind 20951 points

    Hi Mike,

    The VSSOSC is externally driven, you would need to isolate the signal and jumper it to some ground test point on the board for proper functionality. We have not tested this pin as a floating input but treating it as any other VSS signal, still needs to be grounded with optional decoupling depending on proximity to other VSS pins

    Regards,

    Peter

  • 0 in reply to Peter Luong
    Intellectual 355 points

    Have you guys done this kind of rework on BGAs? How would we do that?

    I made a measurement on the chip and was able to verify there was continuity from the VSSOSC and VSS. If I leave it floating, what harm could you foresee by doing this?

  • +1 in reply to Mike Allette
    TI__Mastermind 20951 points

    Hi Mike,

    Personally no. Complexity depends on the fanout for that VSSOSC signal. I assume the signal was connected to power underneath the device and brought to another inner layer as opposed to a surface layer? It would be incredibly difficult to manually rework it. You may be able to get by by only isolating the VSSOSC from the VDDIO, and then relying on the fact that the NMR package has a large number of other connections to VSS. Signal integrity of other nearby signals may be diminished due to the reduced connection to VSS

    Regards,

    Peter