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ADS8167: ADS8167 min conversion time (Tconv)

cuong thai
Prodigy 70 points
Part Number: ADS8167
Other Parts Discussed in Thread: ADS8166, ADS8168,

What is the Min Conversion time? Datasheet only list max converter for ADS8168 (660ns), ADS8167(1200ns), ADS8166(2500ns), and their corresponding cycles time min: ADS8168 (1 us), ADS8167 (2 us), ADS8166 (4us). (source page 10,11 on SBAS817C –NOVEMBER 2017–REVISED NOVEMBER 2019). I want to know what the slowest clock SPI clock without compromising ADC result.

Thanks

  • 0
    TI__Mastermind 37570 points

    Hello Cuong,

    There is no minimum conversion rate for the ADS8167; you can operate at as low a sample rate as needed (example 1 conversion per hour).  The conversion rate is controlled by the timing on the /CS pin, and there is no maximum time limit between conversions.  This also applies to the SCLK frequency; it can be as low frequency as needed and is only limited by the time needed to clock the data out of the ADC before the next conversion cycle.

    Older generation ADCs used the SCLK for the internal conversion clock, and did have a minimum frequency (or maximum period) requirement for SCLK.  The ADS8167 family uses an internal oscillator for the conversion process, which allows SCLK to be fully independent.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0
    Prodigy 70 points

    I think you misunderstood my question. I am not asking for Tcycle, I am asking for Tconv (according to the datasheet. I think It should be called "sample time"). (Tcycle = Tconv+Tacq). For instant, I have my Tcycle at 2 us (for ADS8167), what is the Tconv? I want to slow the ADC SPI_CLK as low as possible (this mean the Tacq as will approach to Tcycle). 

  • 0 in reply to cuong thai
    TI__Mastermind 37570 points

    Hello Cuong,

    The Tconv time for the ADS8167 is fixed and specified as 1200ns.  

    If your total cycle time is 2us, this will then leave 800ns for the acquisition time and the available time to retrieve the conversion result.  If you want to increase the acquisition time and further reduce the SPI_CLK frequency, you could use the ADS8168, in which case Tconv is 660ns.  With a Tcycle time of 2us, this will leave 1340ns for the acquisition time.
    Regards,
    Keith