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ADS8568: Double check on simultaneous sampling

PieterT
Intellectual 640 points
Part Number: ADS8568

Hey everyone,

I want to double check the conversion of the ADS8568.

It looks like the channels are grouped into 2 pairs of 4 channels.

So it has 8 channels in total, but these are grouped into two pairs, does it therefore sample all 8 channels at the exact same point in time or does it do one group of 4 channels simultaneously and then the other 4?

I've seen ADC's that do both and therefore I'm not quite sure as I need to daisy chain three of these to sample 24 channels simultaneously.

Any help will really be appreciated!

  • 0
    TI__Guru**** 181021 points

    Hi Pieter,

    Yes, the ADS8568 is grouped in channel pairs, but its not 2 pair of 4 channels, it's actually four groups/pairs of 2.  Each channel has its own ADC and channel pairs A, B, C and D each have their own CONVST input (pins 37-40).  The CONVST pins can all be tied together allowing you to sample eight channels at the same instance.  With three devices, you could sample 24 channels simultaneously.

  • 0 in reply to Tom Hendrick
    Intellectual 640 points

    Hi Tom,

    Thank you for the reply! This looks perfect.

    I noticed that each channel has an associated AGND, are these all internally connected. Ideally i'd like to measure the voltage deferentially across a range of sources connected in series, something along these lines, where ADC1 and ADC2 in this picture refers two channels of one ADS8568 package with the + and - denoting the bipolar inputs of each channel:

    thanks in advance for any help!

  • 0 in reply to PieterT
    TI__Guru**** 181021 points

    Hi Pieter,

    Unfortunately, the AGND references are all common, so you'd have to reference the inputs to a common point.  Also, the inputs of the ADS8568 are typically driven by an external amplifier, so you could get creative that way.  What sort of voltage(s) will the VSS input be exposed to?

  • 0 in reply to Tom Hendrick
    Intellectual 640 points

    Hi Tom,

    It would be a scaled down max voltage of 1KV.

    Are there any recommended drive circuitry? I'll be using external amplifiers with capacitive load compensation. Not sure if there's any other drive compensation I need to apply.

    Thanks for all the help!

  • 0 in reply to PieterT
    TI__Guru**** 181021 points

    My pleasure Pieter,

    Have you looked through the datasheet and/or users guide for the ADS8568 for an amplifier to pair with the device?  Those documents usually assume fastest sampling rates possible, if you are not going full speed, you may be able to settle for something with a little less bandwidth.