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DP83TC811R-Q1: When VDDIO from 3.3V to 1.8V without any other change, the crystal does not vibrate

Amelie Zheng
Genius 10865 points
Part Number: DP83TC811R-Q1

Hi Team,

My customer now use 811R-Q1 in their system:

When the VDDIO=3.3V,

  • TPD_P(12) and TPD_M(13) connected to external circuit. And 811R-Q1 is slave mode, the external circuit is master mode, it could work and the crystal vibrate.
  • TPD_P(12) and TPD_M(13) disconnected to external circuit. And 811R-Q1 is slave mode, the external circuit is master mode, it still could work and the crystal vibrate

When VDDIO=1.8V without any other change,

  • TPD_P(12) and TPD_M(13) connected to external circuit. And 811R-Q1 is slave mode, the external circuit is master mode, it couldn't work and the crystal can't vibrate.
  • TPD_P(12) and TPD_M(13) disconnected to external circuit. And 811R-Q1 is slave mode, the external circuit is master mode, it still couldn't work and the crystal can't vibrate.

The SCH is as following. As for VDDIO, it could be 1.8V and 3.3V in datasheet, why couldn't crystal work in 1.8V?

  • 0
    TI__Guru**** 192939 points

    Hello 

    Thank you for the query.

    If i understand correctly, the crystal is not oscillating for VDDIO =1.8V and works for VDDIO = 3.3V.

    When i quickly review, i see 6pF capacitor used at C7096 and C7098. I looked at the crystal specifications and the specified load cap is pF.

    Can you ask customer to check the required value. They might have to double the capacitance values for  C7096 and C7098.

    Could you please ask customer to check the behavior with this change.

    In the mean time i will also check if there are any other inputs i can provide.

    Regards,

    Sreenivasa