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Original question:

ADS8598S: Additional group delay for Oversample

ADS8598S: Can the speed of 500kps in parallel mode be achieved

May
Genius 9880 points
Part Number: ADS8598S
Other Parts Discussed in Thread: ADS8598H

Hi Team,

Customer uses ads8598h set to parallel mode os[2:0]000, +-10v range. Because The LPF filter mentioned in this thread (https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1024711/ads8598s-additional-group-delay -for-oversample?tisearch=e2e-sitesearch&keymatch=ADS8598#)


Taking channel 1 as an example, does each conversion require a waiting time of nearly 100us (80us+groupdelay) to convert accurately. If this is the case, can the speed of 500kps in parallel mode be achieved?

Thank you.

Regards,
May

  • 0
    TI__Mastermind 37955 points

    Hi May,

    The 500ksps sampling rate is supported in parallel interface mode on ADS8598H. The delay on the LPF can be seen when your input signal has a fast frequency (e.g. step input) or more analog signals are sharing a same channel of ADC and switching through multiplexers. This is not the case according to the information in the previous thread because Reman mentioned his sampling rate is 10kHz, I assume his input signal frequency is much lower.

    Regards,

    Dale

  • 0 in reply to Dale Li
    TI__Genius 9880 points

    Hi Dale,

    Customer have follow up question, pleas see details below

    In my usage scenario, there are 5 analog signals sharing the same ADC channel and switching through the multiplexer, switching every 30us, does this mean that there is no way to obtain accurate conversion results for the ADS8598H? If so, do you have any suggestions for using this chip?

    If using a multiplexer to switch, there is a step input, how long does it take for each switch to be accurate? Is this related to the input range? +—10v or +—5v.

    Thank you.

    Regards,
    May

  • +1 in reply to May
    TI__Mastermind 37955 points

    Hi May,

    When input channel is switching, the LPF filter on the ADC requires a settling time to settle the input signal, which is approximate 80us for +/-10V range and 120us for +/-5 range. Yes, you will not be able to get the performance specified in the datasheet if you switch them every 30us. The best solution is using multiple channels or ADS8598H ADCs without external multiplexers.

    That's the same settling requirement. Yes, it's related to the input range because the BW of LPF depends on the input range. The customer can check it on an EVM.

    Regards,

    Dale

  • 0 in reply to Dale Li
    TI__Genius 9880 points

    Hi Dale,

    Thank you, there is a follow up question. Under the settings mentioned before, if after each conversion and after reading the data through the DB, can I quickly stabilize the LPF through the reset input, and then perform the next conversion (guarantee the accuracy) premise)?

    Thank you.

    Regards,
    May

  • +1 in reply to May
    TI__Mastermind 37955 points

    Hi May,

    The LPF still need time to settle. The RESET will not help when switching the input channels.

    Regards,

    Dale