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ADS1299: Daisy chain termination

Prodigy 20 points

Replies: 2

Views: 40

Part Number: ADS1299

Hi,

We are desiging three daisy chained device, but want to use same PCB for single snd double chip designs. My question is instead of grounding daisy input if we connect a large enough pull down resistance do same operation. Can I still read the data? Is it possible to get next acquisition?

Thank you,

Metin

  • Hello Metin,

    Thank you for your post.

    You are suggesting to use a pull-down resistor on all DAISYIN pins, while also connecting each DAISYIN to the next DOUT in the chain? I think that would work fine, as long as the pull-down is large enough.

    When another ADS1299 DOUT pin is trying to drive the DAISYIN pin of the next device in the chain, make sure the pull-down is large enough so as not to exceed the maximum digital I/O current in the data sheet (+/-10 uA). For a 3.3-V DVDD supply, this requires at least 330 kOhms. I would use 499k-1M to be on the conservative side.

    When there is not another ADS1299 device driving DAISYIN (i.e. the last device in the chain), the pull-down resistor can be replaced with a 0-ohm, if desired.

    Best regards,


    Ryan Andrews

    Applications Engineer | Precision ADCs 

    Are you working on a bio-potential application? Check out these helpful resources: ADS129x BIOFAQ | ECG Online Training

  • In reply to Ryan Andrews:

    Hi again,

    Thank you for your answer, if I still use same resistor on the last device in the chain, do I still get data right? Can I understand end of data by examine 0s? Can the daisy chain work replacing daisy in GND with pull-up resistor like you suggested?

    You answer is very critical for me? Change the way of my design? 

    Regards,

    Metin