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ADS8688: AIN_xGND and input current questions

Antenna_Head
Genius 12970 points
Part Number: ADS8688


A couple of questions here on behalf of an assigned customer:

1. The Abs Max ratings for the AIN_nGND pin is +/-0.3V.  I assume beyond this level the ESD structure is activated.  If the current into/out of the pin is externally limited, what is the max current the pin can tolerate w/o damaging the device?  I would assuming something in to few mA range?  

2. If AIN_nGND exceeds the +/-0.1V recommended limit, but is less than the +/-0.3V abs max for these pins, do we expect a shift out output code from the ADC?  Understand that this is out of bounds of operation, just wanting an idea of what to expect from the ADC for possible software error checking, etc...

Thanks!

-Steve

  • 0
    TI__Genius 12970 points

    Team-

    Can you please review/respond, thanks!

    -Steve

  • 0 in reply to Antenna_Head
    TI__Guru 66906 points

    Hi Steve,

    Apologies for missing this post. 

    1. We cannot provide a current limit for the input pins. Even if the current is externally limited, the voltage seen by the input pins must be clamped according to the Abs. Max Voltage ratings.
    2. Performance with AIN_nGND outside the typical +/- 100 mV limit is not characterized, so it would be a guess as to which performance parameters may deviate from the Electrical Characteristics table. I would expect the device to appear to function normally, but we cannot guarantee performance in that scenario.

    Regards,

    Ryan 

  • 0 in reply to Ryan Andrews
    TI__Genius 12970 points

    Ryan-

    We really need you to take another run at this; we're looking for guidance here not guarantees.  

    1. It's very common throughout the TI catalog to see this +/- 300 mV abs max.  This rating is for a low-impedance source such as a power supply that could source unlimited current and damage the ESD structures.  Clearly there are levels of current (perhaps uA, which would be low), at which the ESD structures my conduct but will not be damaged.  The applied voltage will be a strong function of temperature.  We are trying to design a network to protect the input and a simple resistor is usually the best answer.  In order to see if a resistor will work, we need to know what current is "non-damaging".

    2. Again, not looking for guaranteed performance, and as clearly stated in the original post, it's understood that this is outside the recommended operating ranges.  The question is what would we expect to happen to the output?  

    Feel free to move this to the internal forum if you helps to be more candid.

    Thanks, -Steve

  • +1 in reply to Antenna_Head
    TI__Guru 66906 points

    Hi Steve,

    Circling back to this thread, the only recommendation we can give as a guideline for such input protection requirements is to limit the current to < 10 mA. I know that some products specify Absolute Max continuous and momentary current limits, but unfortunately, we have not included those in the the ADS8688 data sheet. 

    Regards,

    Ryan