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ADS7885: ADS7886 VDD current issue

Koji Ikeda
Expert 5735 points
Part Number: ADS7885
Other Parts Discussed in Thread: ADS7886

My customer is evaluating ADS7886 and inquires supply current. They pull up to VDD by 1Mohm resister and SCLK and SDO pin is OPEN.

 

When they evaluate some unit, some unit has VDD current around 1mA, while VDD current on other unit is less than 1uA. This looks that ADS7886 turn on with 1Mohm pull up. Does /CS pin have any internal pull down resister or high leakage current? If yes, please let me know how many resistance or leakage current exist internally. Or if their voltage on /CS pin have proper logic level, do you have any idea for the other root cause?

  • 0
    TI__Expert 4405 points
    Ikeda-san,

    Thank you for your post. I will get back to you with a resolution to your query.

    Regards,
    Sandeep
  • 0 in reply to Sandeep Kasargod
    TI__Expert 4405 points
    Ikeda-san,

    The ADS7886 does not go into the 1uA power down state based on /CS pull up.

    The sequence that needs to be driven for the device to enter Power Down Mode is described in Section 8.4.2 and Figure 2 of the datasheet. Could we request the customer to repeat the test after driving this sequence?

    Also, it is not recommended to leave the SCLK pin floating during the measurement. It is best to keep SCLK low after entering the power down mode.

    Thanks.

    Regards,
    Sandeep
  • 0 in reply to Sandeep Kasargod
    TI__Expert 5735 points
    Hello Sandeep-san,

    Thank you very much for your support. I have some questions,

    * Power up with /CS pull up and SCLK open does not enter power down mode. Why both Iq 1mA and 1uA unit exist? If /CS pin pull up does not enter power down mode, the supply current on all unit should flow around 1mA.

    * On the unit with Iq 1mA after power up with /CS pin pull up, when they set this pin to low, they find the Iq increase up to 1.4mA. Why this have such a Iq difference?
  • 0 in reply to Koji Ikeda
    TI__Expert 4405 points
    Ikeda-san,

    The ADS7886 does not have a Power On Reset circuit and we cannot determine the state of the device just after power up. So it is possible that some units power up in their power down state of 1uA and others do not. Pulling the /CS high does not alter this state.

    In order to confirm that the device is performing as expected, could we request the customer to drive the correct power down sequence and ensure that all units draw less than 1uA, with SCLK held low?

    Thanks.

    Regards,
    Sandeep