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ADS7961-Q1: ADC Recommendation

Chuqiang Wen
Expert 5305 points
Part Number: ADS7961-Q1
Other Parts Discussed in Thread: ADS8661, TIC12400-Q1, TMUX1308, TMUX1308-Q1, ADS8665, MUX36S08, ADS7961

Tool/software:

Hi team, 

Customer is looking for a 16 channel ADC with SPI interface. They don't have strict requirement for resolution(8 bit is OK) and accuracy. The main problem for ADS7961-Q1 is that the input analog signal may reach to 12V in worst case. From the datasheet, it seems will damage ADS7961-Q1. Do you have other recommendation on this? 

If no, any solution to protect ADS7961-Q1 from 12V input in worst case? 

Thanks!

Ethan Wen

  • 0
    TI__Expert 5305 points

    Hi team,

    Any feedbacks? 

    Thanks!

    Ethan Wen

  • 0 in reply to Chuqiang Wen
    TI__Expert 8030 points

    Hi Chuqiang,

    There are no 16-channel, 8-bit devices in our portfolio that can support this input voltage directly. Would the customer be open to an ADC+MUX solution? In that case, the ADS8661 is a single-channel, 12-bit, highly integrated device.

    Otherwise, there are various ways to protect the input pins of the ADC. I've linked an application report discussing them below. In the customer's case, they might prefer to implement clamp diodes at each input pin that could exceed the absolute maximum ratings for some period of time. 

    https://www.ti.com/lit/an/slaa593/slaa593.pdf

    Regards,
    Joel 

  • 0 in reply to Joel Meraz
    TI__Expert 5305 points

    Hi Joel, 

    Thanks for your suggestions. 

    Joel Meraz said:
    There are no 16-channel, 8-bit devices in our portfolio that can support this input voltage directly. Would the customer be open to an ADC+MUX solution? In that case, the ADS8661 is a single-channel, 12-bit, highly integrated device.

    For ADC+MUX solution, actually customer is using TIC12400-Q1 right now. But TIC12400-Q1 have leakage current at ADC mode which will add additional offset. The leakage current level is about 11ouA max. 
    Do you have any recommendation on MUX+ADC? Do you think TMUX1308-Q1 is OK? I checked TMUX1308 datasheet, the max leakage current is about 800nA. Based on your experience, do you think this leakage level is low enough? 

    Joel Meraz said:

    Otherwise, there are various ways to protect the input pins of the ADC. I've linked an application report discussing them below. In the customer's case, they might prefer to implement clamp diodes at each input pin that could exceed the absolute maximum ratings for some period of time. 

    https://www.ti.com/lit/an/slaa593/slaa593.pdf

    For this application report, the recommendations are to add clamping diode and OPA, customer cannot accept the additional cost. But do you think it is OK to add an current limiting resistor at the input of ADC to protect the current will not damage device? 

    Thanks!

    Ethan Wen

  • 0 in reply to Chuqiang Wen
    TI__Expert 8030 points

    Hi Ethan,

    In the case of input protection, the clamping diodes can be placed at the input of the ADC, not necessarily the OPA input. I recommend the following video as well, which goes over many options to protect the inputs of the ADC. The ADS8661, ADS8665, and ADS8669 do not need this input protection, as they support up to 12.288V at their inputs. 

    External EOS protection devices

    If going with the ADS8661, or its slower speed, lower price variants, the ADS8665 and ADS8669, the MUX36S08 is a good, low-leakage current option for an 8-channel data data acquisition system. I would consult the MUX team for any more specific recommendations or questions on this device.

    The customer can consider this ADS866x + MUX solution, or they might prefer to stay with the ADS7961 and protect the inputs externally. Let me know the customer's feedback on this proposition, and if they have any other main concerns.

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    TI__Expert 5305 points

    Hi Joel,

    Thanks for your recommendation. 

    Your recommendations are all non-AECQ100 device. This is automotive application. Could you please help recommend 1 channel ADC with AEC-Q100 which can survive at 12V input? 

    Regards,

    Ethan Wen

  • 0 in reply to Chuqiang Wen
    TI__Expert 8030 points

    Hi Ethan,

    I don't believe we have any automotive devices with that high of an input range or integrated over-voltage protection. For this case, I would recommend just using external protection devices, per the TI Precision Labs video linked above, and the ADS7961-Q1. In this case there would be no external mux necessary.

    Regards,
    Joel