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TPS51100: Can you help solve the VTT peak in the shutdown waveform?

Yunjing Wang1
Intellectual 2780 points
Part Number: TPS51100

Hi team,

My customer is using TPS51100, VIN = 5V, VTT = 0.75V, and they find the VTT will appear a peak before decrease to zero,but the test result in datasheet does not exist this peak.

This peak will cause error to their SVS circuit error, can you help check what reason can cause this issue? And how to eliminate this peak?  

Thanks and best regards

Yunjing

  • 0
    TI__Mastermind 24075 points

    Hi Yunjing, 

    I suspect the peak is caused by VTT leakage current from DIMM side. 

    What's the power off sequence of VDDQ, VIN, S3 and S5? Can you provide the waveform of these signals with VTT signal?

    Thanks

    Qian

  • 0 in reply to Qian Chen
    TI__Intellectual 2780 points

    Hi Qian,

    Thanks for your reply, pls check below waveform with VDDQ, VIN, S3, S5 and VTT. 

    And what can cause this leakage current? How can we prevent this?

    Thank you

    Yunjing

  • 0 in reply to Yunjing Wang1
    TI__Mastermind 24075 points

    Hi Yunjing, 

    The waveforms show VIN_5V/S3/S5 turns off first, the VDDQ turns off after a few ms.

    Once VIN_5V, S3 and S5 turns off, TPS51100 VTT pin is high impedance. Because VDDQ is still supplying DIMM chip, there is a VTT leakage current coming from DIMM, and this leakage current charge VTT up. 

    This VTT leakage current existing on many DIMM modules. We see similar behavior on many customer project. 

    Can you ask customer to turn off VDDQ first, then turn off VIN_5V/S3/S5?

    Thanks

    Qian