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ADS1248 - Accidentally Exceeded voltage for input reference - Now Analogue Inputs aren't reading correctly

Steven Bramsiepe
Prodigy 120 points
Other Parts Discussed in Thread: ADS1248

Hello Everyone,

First of all thanks for anyone who can help.

As mentioned in the title i have a ADS1248 which was going to be used for a 4 point temperature measurement. However today while testing of reference inputs i accidentally exceeded the voltage with an input of ~10-11 V (mixed up channels on a power supply). This caused a spark as i connected it to a wire (only to the wire not on the board) which was connected to a pin. After this, the difference between Analogue input 0 /1 was not reading correctly. Where a scope was reading a value of ~5 mV for a ~110 Ohm resistor at 50 uA, (IDAC)  the ADC was ~0.48V which seems to be nonsense. I also noted that the voltage range seems to have a lower limit of ~-1.75 V.

Another thing was some of the reference pins has changed voltage except the internal reference output from the "Int Ref" terminal. Also noted that when no current was output from the IDAC there was still a voltage over AI0/1 when connected to AGND.

Obviously I am concerned I have just broke it or is there something that can be done. Such as a full reset or something similar?

The problem definitely seems to be in the analogue inputs as the scope verified the IDAC was outputting correctly.

Again thanks for any help or replies.

Steven

  • 0
    TI__Guru* 92715 points
    Steven,


    My first guess is that the device is now broken. I'd point out the Absolute Maximum Ratings on page 2 of the ADS1248. Most digital circuits don't take too kindly to high voltages. Generally, I'd advise you to un-solder the part off the board and put on a new one. However, you should also be concerned that something else on the board is also damaged, even if there's no evidence of that right now.

    If you connected the high voltage to one of the reference pins, it's possible that just that one pin that's damaged, and the alternate reference pin might be functional. However, I would guess that the reference sampling part of the circuit is damaged too. With that high of a voltage, other sections are likely damaged as well.

    You could test it, but I'd say that you need to remove and replace the part. 10V is a pretty high voltage for the part to survive, especially if the supply could source current.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 120 points
    Thanks Joseph for your reply,

    After replacing the ADS1248 chip on the board it seems to be working fine again. From that i'm currently assuming that another part of the board isn't also broke except i have yet to try that reference pin so i will find out soon.

    Again thanks for your reply,

    Steven
  • 0 in reply to Steven Bramsiepe
    TI__Guru* 92715 points
    Steven,


    Ok, I'm glad you were able to get up and running again. If you have any other questions. Please feel free to post back.


    Joseph Wu