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ADC32RF55: When does the VCM pin of the ADC start to output 0.35 V (typ)?

Sayaka Kose
Prodigy 40 points
Part Number: ADC32RF55
Other Parts Discussed in Thread: LMH5401

Tool/software:

I am using the original board using ADC32RF55.

After supplying power to the ADC on the board, I checked the VCM pin and found that 0 V was output.
Also, looking at the 0x298 register of the ADC, calibration failed.

When does the VCM pin start to output close to 0.35 V?
Also, does calibration need to be completed for the VCM to output 0.35 V?

Thank you and best regards,

  • 0
    TI__Mastermind 38690 points

    Hi Sayaka-san,

    I am not sure when in the register write sequence does the VCM go from 0V to 0.35V.

    I would have to check with systems or design to find out.

    You can also put a script together and step thru each reg write sequence to find this out when this happens.

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Prodigy 40 points

    Thank you for your reply, Mr. Rob

    We are checking the operation with 2 boards, but sometimes SYNC fails.

    The VCM pin is connected to a differential high-speed amplifier (LMH5401) to adjust the amplitude of the signal to the ADC.
    Previously, both boards failed at low frequency, but now the 1st board always fails.
    When we checked the VCM terminal after supplying power to the ADC on the board at the time of failure, 0 V was output.
    Success: about 0.2 V at power-on → 0.35 V after sequence →SYNC succeeded
    Failure: 0 V at power-on → 0 V after sequence →SYNC failed
    When we looked at the 0x298 register of the ADC at the time of failure, calibration failed.
    When in the register sequence does the VCM pin start to output near 0.35 V?(wouldn't you check it?)
    Also, is it necessary to complete calibration for the VCM to output 0.35 V?

    Best regards,

    Sayaka Kose