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ADS1293: AC Lead-Off Detection reading IN4 Error

Ali Şerbetçi
Prodigy 20 points
Part Number: ADS1293


Hello,

I set registers of Ads1293 Ic to read ERROR_LOD (Lead-Off Detect Error Status). I use application called 9.2.1 3-Lead ECG Application and set registersters 9.2.1.2 Detailed Design Procedure according to datasheet of Ads1293. 

When I connect IN1(RA),IN2(LA), IN3(LL) and IN4(RL) ERROR_LOD is read as 0x00 as expected. When I disconnected IN1, IN2 and IN3 ERROR_LOD register points that which Lead has disconnection/error but when IN4 is disconnected it shows 0x0f means that all leads have connection error although IN1, IN2 and IN3 are connected.

Could you please enlighten me what can be reason of the situation? 

Yours Truly,
Ali Serbetci

  • 0
    TI__Mastermind 19815 points

    Hi

    May I ask are you using ADS1293 evaluation kit/board(EVM) or a customer PCBA?

    And, are you trying to use which Lead-off detection referring to datasheet page 25 to 27:

    1) DC lead-off detect,

    2) analog AC lead-off detect

    or

    3) digital AC lead-off detect.?

    ------------------------------

    If you are using IN4 for RLD, which is encouraged, because RLD can help to bring the Unit/Subject Under Test/Measurement(UUT or UUM) into/within a known stable voltage, so that the UUT or UUM is not floating at an unknown voltage(i.e. could be high or low and outside the measurement range/window), which could make both the ECG signals and Lead-off detection unstable.

    So, once you removed the RLD, the UUT or UUM becomes floating at an unknow voltage, which could cause the unstable outcome.

    Highly suggest to take a look and study the Right Leg Drive(RLD).  You may make analogy/relate to the concept of using and ESD wrist strap.

    Thanks

  • 0 in reply to ChienChun Yang
    Prodigy 20 points

    Hi Yang,

    I use custom board which is designed for custom application also to confirm firmware I use ready ads1293 board on the market called "CJMCU-1293".

    Yes I am trying to use which Lead-off detection referring to datasheet page 25 to 27:

    2) analog AC lead-off detect.

    I use IN4 for RLD. Could you please tell me solution of the situtaion? Should I connect IN4 to CH3 for confirming LOD then switch to RLD after reading LOD register?

    Do you have any suggestion please?

    Yours Truly,
    Ali Serbetci

  • 0 in reply to Ali Şerbetçi
    TI__Mastermind 19815 points

    Hi,

    To use Analog AC Lead-off detection, please follow datasheet page 25~26 -  8.3.17 Analog AC Lead-Off Detect

    pay particular attention to page 26-

    "

    The comparator outputs can be accessed at the OUT_LOD[x] bit of the ERROR_LOD register. A high comparator output signal indicates that the AC voltage at the excitation frequency is larger than the programmed threshold, which indicates that the lead is not well connected.

    The lead-off detection circuit requires a low-impedance return path from the right-leg electrode-to-ground, such as a voltage reference or the RLD amplifier output. Without a proper low-impedance return path for the LOD currents, all enabled LOD pins will report a lead disconnected.

    "

    If you are using IN4 for RLD, what might be the "RLD_CN register and SELRLD bit" settings?

    And, do you connect the IN4(RLD)'s electrode to right leg node of the ECG simulator?

    ---------------------------------------------------

    it's highly recommended to use ADS1293 evaluation kit/board(EVM) and ECG simulator to do some tests and evaluation to get familiar with before diving into an customer PCBA.

    Thanks