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ADS1234: ADS1234 number of SPS per chanel

Ernesto Ramirez
Prodigy 70 points
Part Number: ADS1234

hello everyone, in the datasheet of the ads1234, note that the device handles 80 samples per second, my question is if these 80 samples are for the 4 channels, (20 samples per channel), or 80 samples for
each channel.

Thanks in advanced

  • 0
    TI__Guru** 113765 points

    Hi Ernesto,

    As the ADS1234 uses a mux to measure the four channels separately the cycle time will be reduced greatly from 12.5ms (80sps).  The ADS1234 uses a sinc4 digital filter, so the digital filter will not be fully settled until after the 4th conversion completes.  The timing is demonstrated in the ADS1234 datasheet on page 17 and shows what happens when the mux is changed in Figure 32.  First there is a small setup time before conversion starts following a mux change which can range from 40-50us.  DRDY/DOUT can be used as the signal for when valid conversion data are ready to be read out from the ADS1234.  The nominal time is 51ms at 80sps data output rate. So when the mux is changed, DRDY/DOUT will go high and 51.05 ms later will go low signaling a valid data are available.  If the mux is not changed, the next transition of DRDY/DOUT from high to low takes place at 12.5 ms after the previous.

    Added to this time will be the actual time it takes to read out the conversion result prior to the next mux change.  Depending on SCLK speed this could range from 10 to 50us or more.  Let's say 50us which would be added to the 51.05ms so that the time of each channel averages to 51.1ms.  So for all four input channels to convert and be read will take about 204.4ms or 4.89 measurement cycles per second to measure all four input channels.

    Best regards,

    Bob B