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Original question:

ADS1299: Real time lead off detection

ADS1299: lead off detection

bdsong2021
Prodigy 10 points
Part Number: ADS1299

Hi, TI's experts，I have some trouble with ads1299 for lead-off detection. My device is the same as Referential Montage. I replace a resistor between normal electrode and references electrode.Some issues are like below:

  1. For the DC 6uA current to detect resistor, can you provide a detailed explanation of the connection position of the pull-up or low-down resistors, using Referential Montage as an example.
  2. When I select AC mode to detect resistor,there is almost no difference in the data collected from all channels, regardless of whether external resistors are placed or not. If external resistors are not placed, I think it should be impossible to form a current path. Can you help me check the Register Configuration？

-reference signal is connected to negative input via SRB1；

-LOFF: 0Ah(6nA，31.2Hz), CHxSET: 60h, BIAS_SENSP:01h, BIAS_SENSN:01h, LOFF_SENSP:01h, LOFF_SENSN:01h, LOFF_FLIP: 00h, CONFIG4:00h.

The image is the waveform I measured.

  • 0
    TI__Mastermind 49926 points

    Hello,

    Thank you for your post!

    Debugging lead-off detection issues is usually very specific to how one's system is configured. I would suggest first reviewing some of the helpful collateral I've linked below. You should be able to trace where the lead-off current is flowing and confirm where the DC bias of each node sits. In most cases, lead-off issues present when the connected inputs are not biased to a known common-mode, or when the lead-off currents do not have a return path. This return path can be through another current source of opposite polarity (LOFFP vs. LOFFN) or through the BIAS amplifier. If the inputs are connected to the BIAS electrode, the BIAS amplifier must be able to sink/source any additional current that is not balanced by the LOFFP and LOFFN currents.

    We have some useful application notes and articles on this topic linked on our ADS129x BIOFAQ page on E2E.