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ADS1158 - DLY bits seem to not have any affect

Joshua Anzicek
Prodigy 40 points
Other Parts Discussed in Thread: ADS1158, OPA2365

Hello, I have integrated an ADS1158 into our product and the setup is as follows:

-Unipolar operation

-External ADC amplifier (OPA2365 buffer external to the part) - Bypass bit = 1

-START = LOW

-Configured for scanning mode (not fixed channel)

-DRATE = b11 (23739 SPS)

-Using pulse convert command through SPI to trigger measurements

Here's my question / issue:

The timing from pulse convert command transfered to DRDY line low = 40.4uS consistently.

No matter what I set the DLY bits to there is not change in this timing.  I would expect that a DLY of b111 would cause a much slower measurement cycle and allow more settling time.

The reason I am asking is that I may consider removing the external buffer amplifier, but then I would need the additional settle time.  I tried setting bypass to 0 and DLY still had no affect on the timing of DRDY.

Thanks for your help.

  • 0
    TI__Mastermind 44610 points

    Hi Joshua,

    Welcome to the TI E2E forums!

    The ADS1x58 data sheet is not very clear about the switch time delay when used with pulse convert mode. For reference, here is what is in the data sheet:

    When pulse converting, where one channel is converted with each START pin pulse or each pulse command, the application software may provide the required time delay between pulses. However, with Chop = 1, the switch time delay feature may still be necessary to allow for settling.

    After looking into this and replicating the same observed behavior as you described, it appears that the switch time delay is IGNORED when using pulse convert mode (except when CHOP = 1). Therefore, I believe if you are are using pulse convert mode, you'll need to implement a software delay before sending the pulse convert command.

    So perhaps it would be better if the data sheet read like such:

    When pulse converting, where one channel is converted with each START pin pulse or each pulse command, the application software must provide the required time delay between pulses. However, with Chop = 1, the switch time delay feature will still occur between conversions to allow for settling.

    Best Regards,
    Chris

  • 0 in reply to Christopher Hall
    Prodigy 40 points
    Thank you for the quick follow up Chris. It is correct that I am not using CHOP currently. Since I'm single ended I don't think it does anything for me. We are providing the necessary delay in SW, I just wanted to make sure that there wasn't a feature I was using incorrectly. Thanks again,
    Josh