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ADS8668: About ADS8668 input pin rating rang

Jimmy WANG
Genius 3505 points
Part Number: ADS8668

Tool/software:

Hi team,

Hi team,

The customer has a question about the input rang of AD8668 from  ADS8668 user guide.

If connect negative input to GND that input voltage just applying only 100mV? or accept 100mV offset into negative input.

Another problem is that pin36 of the customer's ADS8668 is easily damaged. Where do you think the problem is?

  • 0
    TI__Guru**** 175371 points

    Hi Jimmy,

    The snippets above seem to be from the older version of the ADS86xxEVM.  The negative inputs of the ADS8668 can swing +/-100mV MAX (see section 7.5 (AIN_nGND) - normally these inputs are tied directly to ground, if you have a small common mode voltage (i.e. +/-100mV) then you can use the device in a pseudo differential mode to remove the common mode signal.  It's not really intended for a DC offset.

    As for pin 36 getting damaged, you'd have to provide some additional details (schematic, conditions, etc.) to understand what the issue may be.  Pin 36 is the SDO, it should be able to drive up to 10mA without any issues.

  • 0 in reply to Tom Hendrick
    Genius 3505 points

    Hi Tom,

    Could you explain more about how you can use the device in a pseudo-differential mode to remove the common mode signal?

    The customer's schematic as below. pls help to check. thanks 

  • 0 in reply to Jimmy WANG
    TI__Guru**** 175371 points

    Hi Jimmy,

    Sorry for the really bad drawing, but assume your VIN_p and VIN_n had a common mode voltage of +/-100mV, the 'pseudo differential' mode would help remove the common mode voltage from the conversion results.  The two black lines below would be the inputs, the red line would be the result in the end (with some artistic license...).

  • 0 in reply to Tom Hendrick
    Genius 3505 points

    Hi Tom,

    Thanks for your explain about my question. Could you help check schematic why customer feedback 36 pin easy to damage? 

    Need to add some ESD or something? thanks 

  • 0 in reply to Jimmy WANG
    TI__Guru**** 175371 points

    In the schematic you provided I see nothing that would damage the SDO pin.  You would need to provide more details.