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AM572x EVM Revision

Nathan Rabenold
Intellectual 745 points
Other Parts Discussed in Thread: TPS659037

Hi-

I was reviewing changes made to the AM572x EVM processor module in Revision A3.  Capacitors C452 and C453 were changed from 12pF to 16pF.  However, the TPS659037 design checklist and crystal datasheet imply that a load capacitance of 10pF should be used (with device pad assumed to be <1pF).  Can you explain the reasoning behind this change?  Was there a performance issue with the original capacitor value?

Thank you for your assistance,

Nate

  • 0
    TI__Guru**** 393215 points
    The original crystals selected were not available as we began to ramp production on Processor Module revision A3. So we selected acceptable substitute crystals that were in inventory. The footprint of Y9 was changed because it was very difficult to find a crystal in the original package size that was currently in inventory and would meet all of the crystal requirements defined in the data sheet. For example, crystals in larger sized packages normally provide a lower ESR.

    The new crystals were designed to operate with different load capacitance than the original crystal, so the load capacitor values were changed based on the specified load capacitance of the new crystal.

    In the case of Y3, we decided to use Kyocera CX3225GB22579D0HEQCC which requires a load capacitance of 8pf. The PCB, AM572x package, and AM572x oscillator input contributes about 2pf of loading so we need the remaining 6pf to be provided by C102 and C103. Since these capacitors provide an effective series capacitance load to the crystal, the value of C102 and C103 were changed to 12pf.

    In the case of Y9, we decided to use TXC 7M‐16.384MEEQ‐T which requires a load capacitance of 10pf. The PCB, PMIC package, and PMIC oscillator input contributes about 2pf of loading so we need the remaining 8pf to be provided by C452 and C453. Since these capacitors provide an effective series capacitance load to the crystal, the value of C452 and C453 were changed to 16pf.