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ADS8866: Simultaneous Sampling using multiple ADCs in daisy chain

rlc372
Prodigy 50 points
Part Number: ADS8866

Hi,

I am planning to use ADS8866 to achieve local sampling close to the sensor. Using daisy chain seemed to guarantee that the conversion will start at the same time for all sensors.

Based on the manual, this is not sure. It is mentioned that there is an internal clock for the ADC conversion and the SCLK is only for the serial operation. Thus, the conversion does not share the same clock. 

I guess when the CONVST activates the conversion, the S/H saves the value at the S/H. Does the switch close to charge the hold capacitor in an internal clock event?

Is there any reset of the internal clock when the ADC starts the conversion via the CONVST pin? 

Thanks in advance!

  • 0
    TI__Mastermind 36240 points

    Hello,

    The converter starts the conversion on the rising edge of CONVST.  It is true that each ADC will have a slightly different internal clock rate and each will take a slightly different time to convert the result, but all ADC's will sample the input at the same time, and will be synchronized.

    The sampling rate is equal to the frequency of CONVST, and does not depend on SCLK or the internal conversion clock.

    To answer your question, the precise moment when the input sampling capacitor switches from the analog input to the internal HOLD is the rising edge of CONVST pin, and does not depend on the internal conversion clock or SCLK.

    Regards,
    Keith Nicholas
    Precision ADC Applications