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ADS1294: ADS129x lead-off circuit details

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Replies: 4

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Part Number: ADS1294

Hello,

I am trying to implement DC current lead-off detection in ADS1294, but have some difficulty to understand details related to comparators. I have found nice picture in the sbas459k datasheet, but comparators inputs are not described, therefore I have described them regarding to my understanding and assumed 20% and 80% thresholds like below:

I have found following description in the sbaa196a "Understanding Lead-Off Detection in ECG" application report:

My understanding is as follows:

- when VINP is disconnected, then it is pulled up to AVDD by the DC current source and it's voltage is >80% of VDD. Therefore LOFF_STATP = 0.

- when VINN is disconnected, then it is pulled down to AVSS by the DC current source and it's voltage is <20% of VDD. Therefore LOFF_STATN = 0.

So, voltage at VINP must be <80% of VDD, and voltage at VINN must be >20% of VDD to be detected as connected.

Can anybody confirm if my assumption of comparators inputs description and understaing of the circuit is correct?

Thanks & regards!

Maciej

  • Hello Maciej,

    Thanks for your post. 

    LOFF_STAT = 0 means the electrode is connected. When the channel inputs are pulled above AVDD or below AVSS, the corresponding LOFF_STAT bit will be set to 1.

    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:

    Hello Ryan,

    Thank you for your feedback and clarification!

    Based on your answer I have corrected description of comparators' inputs to have their states = 0 when connected. Is the description below correct?

    Thanks & regards,

    Maciej

  • In reply to Maciej Lasota:

    Hello Maciej,

    Yes, that is how the ADS1294 comparators will operate.

    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:

    Thanks Ryan!

    Best regards, Maciej

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