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Part Number: ADS1294
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!
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.
Applications Engineer | Precision ADCs
Are you working on a bio-potential application? Check out these helpful resources: ADS129x BIOFAQ | ECG Online Training
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In reply to Ryan Andrews:
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,
In reply to Maciej Lasota:
Yes, that is how the ADS1294 comparators will operate.
Best regards, Maciej
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