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ADS1258 Auto-Scan Data Rate confusion

David S52637
Prodigy 30 points
Other Parts Discussed in Thread: ADS1258

Hello

The data sheet for this device specifies a maximum channel sampling rate of 23.7 ksp/s.

Is this the max sampling rate for each channel specified with all 16 single ended channels active ?

What happens if I just want to sample 8 channels or 4 channels ? Does the max auto scan sampling rate/ch increase or is it always limited to 23.7 ksp/s ? I would have assumed that it would double for 8 and double again for 4 channels but it is not clear from the data sheet.

Also is the heat tab on the bottom of the chip electrically isolated from the rest of the pins ?

Thanks in advance

David

 

  • 0
    Prodigy 30 points

    Just looking at the datasheet for the ADS1258 again. It says the following;

    The ADS1258 is a flexible, 24-bit, low-noise ADC optimized for fast multi-channel, high-resolution measurement systems. The converter provides a maximum channel scan rate of 23.7kSPS, providing a complete 16-channel scan in less than 700us.

    This tells me that the maximum rate at which the MUX can be switched is 23.7k . Does this mean that each channel captures 1 sample before the MUX is switched to another channel ?

    Does this also mean the sampling rate for each channel assuming 1 sample per channel is 23.7/16 or 1.48 ksps ??

    Am I reading this correctly ?

    regards

    David

     

     

  • 0 in reply to David S52637
    TI__Mastermind 43915 points

    Hi David, 

    The maximum data rate is 23.7kSPS per channel. So, if you want to convert all 16 channels, it would take a little under 700us or 1.48kSPS as you note. Now, you can add additional delay in between mux transisitions if you would like to give additional time for your filter (whatever you place between MUXout and ADCin) to settle.Adding delay will decrease your data rate to. See table 5 on page 20 for more details. 

    From a software side of things, you can enable the STATUS byte which will output the channel ID bits so you know exactly which channel you are reading out. The channel pointer index is on page 33 of the data sheet. This is the order that the mux will cycle through when you run the ADC in Auto-scan mode. 

    Regards,

    Tony Calabria 

  • 0 in reply to Tony Calabria
    Prodigy 30 points

    Hello Tony

    Thanks for your reply. I guess what through me off is that the data sheet states "Single-Conversion Settled Data" so you automatically assume that there is no latency in channel switching mode when in reality there is a 5 cycle latency due to the settling time of the filter according to your reply in the following thread.

    http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/p/2896/9994.aspx#9994

    Your explanation in the above thread would be a valued addition to the data sheet.

    regards

    David