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BQ32000: BQ32000 test fail

Lawrence He
Expert 2740 points
Part Number: BQ32000

Hi, Support Team

We would use DIODES PT7C4339WEX as your 2nd source and end cuatomer requests us to choose one solution for external capacitors.

But, crystal vendor told us it is impossible from the test results.

Because we should choose “No Load” using TI BQ32000DR and choose 10 pF using Diode PT7C4339WEX according to the test results.

Could you review the test results and advise us how to choose?

Schematic:

result:

TI BQ32000DR:

DIODES PT7C4339WEX:

if any suggestion, Please advsie me.

Thanks,

Best regards,

Lawrence

  • 0
    TI__Guru* 85130 points

    Hi Lawrence,

    I suggest keep the 10pF external load capacitors for both parts. 

    Our device support crystal calibration, after calibration, we can pull the ppm back to a single digit accuracy.

  • 0 in reply to Noel Fung
    Expert 2740 points

    Hi, Noel

    If we use the 10pF external load capacitors with TI BQ32000DR, the crystal vendor told us there is possibility the crystal doesn’t oscillate because the negative resistance is too small.
    Could you have any comments for this?

    if any, Please advise me.

    Thanks,

    Best regards,

    Lawrence

  • 0 in reply to Lawrence He
    TI__Guru* 85130 points

    Hi Lawrence,

    I believe our RTC has switched-capacitors to adjust crystal frequency, when calibration is done the ppm error will be reduced so at that time, the negative resistance should increase. 

    To be honest, I am not 100% sure the calibration mechanism, our team did not design this chip, I don't have the detail of this chip.

    If possible, do some experiments to confirm. 

    BTW, how was the negative resistance determined? Isn't it a calculated value based on the ppm error and crystal parameters?