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Original question:

ADS1292: ADS1292 RESP2 register

ADS1292: saturated channels

Jacob Fortin
Prodigy 70 points
Part Number: ADS1292

Hi,

Using ADS1292, I've encountered a similar issue as https://e2e.ti.com/support/data-converters/f/73/t/867995?tisearch=e2e-sitesearch&keymatch=ads1292%20vref.

Our guess is that the chip is defective, but we're not quite sure of its comportment:

  • We can write/read all register without any problems
  • The chip is being supplied at 3.3V (AVDD and DVDD)
  • The chip behaves as expected on reset (registers return to default value)
  • When starting conversion, the drdy pulses as expected

Problem is, no matter the input (channel shorted, test signal, temp sensor, normal mode, ...) the conversion always return either 7F FF FF or 80 00 00 for both channel (both channel's gain are set to 1).

When probing, we realized that VCAP2 is at 5.28V, Vref and VCAP1 are at 0V. What we don't understand is how are we able to communicate and start conversion if the chip has been damaged?

Also, what might have damaged the chip? I've included our schematic for reference.

Thanks a lot!

Jacob

  • 0
    TI__Mastermind 47625 points

    Hi Jacob,

    From the symptoms you've described, it sounds like something on the analog portion of the chip has been damaged. Most likely the reference since it is 0V. Since the reference is 0V, it makes sense that the result shows a +/-full-scale voltage. You are able to write registers and see DRDY pulses since these functions are controlled by the digital side of the device. 

    Schematic looks fine to me. 

    Over voltage on either the analog supply pins or analog input pins could cause this damage. Incorrect handling of the device during manufacture such as not wearing a wrist-strap, too much heat when soldering, excessive moisture during storage - any of these could cause an issue. Are you seeing this behavior on multiple boards or just one? Have you tried replacing the chip to see if it fixes the issue? 

  • 0 in reply to Alexander Smith
    Prodigy 70 points

    Hi Alexander,

    Sorry for the late reply. We changed the chip for a new one, but it didn't solve our problem. We used flux while soldering and a temperature of 245 fahrenheit. Could this cause any problem? The temperature is well under the max of 150 celsius but could the flux produce excessive moisture?

    Thank you for your time.

    Jacob

  • 0 in reply to Jacob Fortin
    TI__Mastermind 47625 points

    Hi Jacob,

    I don't think that's the problem. Is this BGA or TQFP package?

    Did you buy the chips direct through TI.com or through a distributor? Is it an authorized distributor?

    One other thing I noticed is that the negative RESP channel is connected to GND, which may cause issues. Try lifting this pin and see if it helps.

  • 0 in reply to Alexander Smith
    Prodigy 70 points

    Hi Alexander,

    We finally found our problem. Turns out it was a footprint issue, the library we used was defective. One side of the chip would not connect properly due to its footprint being slightly offset.

    Thank you for your help.

    Jacob

  • 0 in reply to Jacob Fortin
    TI__Mastermind 47625 points

    Hi Jacob,

    Glad to hear that you found the issue, thanks for letting me know! Let us know if you have further questions.