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Original question:

ADS1298: TESTP_PACE_OUT1 and TESTN_PACE_OUT2 pins unused

ADS1298R: Unused TESTN_PACE_OUT2 pin

Denn
Prodigy 230 points
Part Number: ADS1298R

Hi,

We have a problem and trying to find the reason behind it...

In our design we are using hardware pace detection and only one channel to detect the pace maker signals . Thus, TESTN_PACE_OUT1 is used but TESTN_PACE_OUT2 is not. As still instructed in the latest datasheet  (SBAS459K –JANUARY 2010–REVISED AUGUST 2015) on ADS1298R page, these pins, if unused, must be connected to AVDD. In our design we did connect TESTN_PACE_OUT2 to AVDD.

While trying to get our design work, we noticed that our AVDD is -0.690v rather than +2.5v. We disconnected the regulator that generates +2.5v from the system, it indeed generates the expected voltage, so there is nothing wrong with it and problem is somewhere beyond generation. In our previous designs, we used to use 2 channels for pace detection and had no problem. The only difference is that TESTN_PACE_OUT2 pin is now connected to AVDD.

While looking for an explanation for this voltage level problem, I noticed that in one of the threads it is stated that TESTN_PACE_OUT2 pin should left floating when unused. I am now wondering if this could be reason behind our problem. We followed the instructions in datasheet and we worry that if there was a mistake, it is still not corrected. 

I will be glad if you please make a comment. 

e2e.ti.com/.../2071200

Best regards,

Denin

  • 0
    TI__Genius 11550 points

    Hi Denin,

    Thanks for pointing out the issue. As stated in the reference post, the TESTP_PACE_OUT1 and TESTN_PACE_OUT2 should be left floating if they are not used. Also, the typo in the datasheet needs to be updated. Sorry for the confusion.

    Thanks

    -TC

  • 0 in reply to TCT
    Prodigy 230 points

    Hi TCT,

    Thank you very much for the confirmation.

    Would you mind making a comment about the problem we have? Could connecting the pin to AVDD cause such a voltage problem? We have PCBs that are not yet powered. So, if AVDD causes some kind of damage, we will try to somehow break the connection between the pin and AVDD before we power the remaining of the PCBs up. 

    Your comments will be very important regarding how we will move on. Looking forward to hearing from you. 

    Regards,

    Denin

  • +1 in reply to Denn
    TI__Genius 11550 points

    Hi Denin,

    There may be a situation where the PACE amplifier output is driven to mid-supply (AVDD+AVSS/2), leading to the pin drawing excessive current from the AVDD connection. By default, the device should power up with all the PACE switch disconnected, and the PACE amplifier turned off (Pace Detect Register). I recommend breaking the connection for all the subsequent testing.

    Thanks

    -TC

  • 0 in reply to TCT
    Prodigy 230 points

    Hi,

    Luckily ADS1298Rs are not damaged. The problem was with the power supply stage. Boards are working fine now. However we hope to see the datasheets corrected soon. Thanks for your assistance.

    Regards,

    Denin

  • 0 in reply to Denn
    TI__Genius 11550 points

    Hi Denin,

    Thanks for the update and glad that you are able to get the board working as expected. 

    Thanks

    -TC