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ADS1293: DC open lead detection without RLD

Franz Schellhase
Expert 3605 points
Part Number: ADS1293

Hi team,

Can you have a look at the following customer inquiry, please?

We are currently working on a project in which we would like to incorporate the ADS1293.

I have two questions:
1) OpenLead
We want to use the ADS1293 in a pure 3-Lead/3-Channel (without feedback -RLD) configuration:

This works fine so far.

Now we have a problem with the OpenLead detection. According to the datasheet neither the DC- nor the AC- detection of the ADS1293 would work (because no RLD). Only the variant by means of impressing AC voltage and subsequent analysis (FFT/narrowband filter) would work. But this would cost a lot of energy which we don't want to spend (or can't).

Do you have another solution as a suggestion?
Is it possible to use the DC version by connecting the RLD internally?

2) Reference pin (CVREF):
We would like to use the voltage at the reference pin (CVREF) for other purposes.
Actually the datasheet is very clear here ("The CVREF pin must have a 1 μF bypass capacitor-to-ground with low ESR and is not designed to be loaded with other circuitry.").
Is it still possible to decouple the voltage via a high impedance converter?

Thank you,

Franz

  • 0
    TI__Mastermind 19815 points

    Hi,

    So when customers say lead open, they mean lead off detection(a more common term in ECG product).

    1) if customer means that they don't have and don't want to use RLD electrode to attach to subject, then one thing they could try is using

    a. external approach - tie RLDOUT output pin to the signal input pins via resistors. 

    b. internal approach - use the SELRLD bit to route the RLDOUT to input pins internally according to datasheet page 23 "The output of the RLD operational amplifier is always connected to the RLDOUT pin, and in addition, can be connected to one of the IN1-IN6 terminals by programming the SELRLD bit in the RLD_CN register."

    2) May I ask what is " high impedance converter"?  What might be the purpose for that? As datasheet suggested, it's not recommended and may affect/disrupt the stability&cleanness of VREF.

    It's not suggested, but customers could do dome experiments&tests and data collection&analysis.

    Thanks.