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ADS1230: pin 1 VDD is not connected

Part Number: ADS1230

Hi team,

I got a question from customer.

"we've run into a production anomaly with a digitizer circuit in which we are utilizing the ADS1230 .
Pin 1 -VDD is supposed to be connected to 3.3V and as a result of a layout error it is left un connected .
Nonetheless ,the ADS1230 continues to function correctly at all temperatures (-40 + 80C ) while the voltage at VDD pin 1 is 2.6VDC. It appears that the 3.3V is routed from one of digital inputs via a protection diode to the VDD pin 1, which can explain the 0.7 drop out .
The pin 1 is showing 2.6V which is below the 2.7 threshold in the data sheet .Clearly we're going to correct this mistake ASAP in production, but my question relates to potential reliability issues about field units :

What is the risk for reliability issues ?
Do you see any risk in operating with the ADS1230 in the above scheme ?
is there a long term associated risk with routing the current through the protection diodes , taking into consideration that the current consumption of the digital block is~100uA ?"

Thank you very much for your help.

Best regards,

  • Hi Zhonghui,

    The ADS1230 will not be damaged as long as the input parameters are kept within the absolute maximum ratings. However, since AVDD is not at 3.3V, you would need to ensure that the input signals never exceed the actual AVDD voltage (2.6V in your case). This would be a violation of the absolute max ratings. For example, if you applied a 3V signal to the ADC when AVDD = 2.6V, you could theoretically damage the ADC.

    The ADC core was likely not designed to operate at <2.7V, so any behavioral changes are unclear. In general I would expect uncertain ADC operation: it might work okay most of the time, but there is no way to know what combination of settings (temp changes, input signals, etc) may cause the ADC to stop operating properly since you are outside of the recommended operating conditions.

    I would avoid operating the ADC in this way at all costs to ensure proper ADC operation.

    -Bryan

  • Hi Bryan,

    Thank you for your feedback ,

    I fully understand that this issue must be corrected ASAP in production ,

    However , as I mentioned pin 1 VDD is not connected but we're still measuring a voltage of 2.6 Vdc at this pin ,
    The digital input gain is at 3.3Vdc .

    Do you have an explanation about why we are seeing a 2.6 Vdc voltage ,
    and as I mentioned , it is working well at all temperature conditions , we've already tested about 20 boards .

    Thanks .

    Best regards,

  • Hi Zhonghui,

    It appears that the 3.3V is routed from one of digital inputs via a protection diode to the VDD pin 1, which can explain the 0.7 drop out .

    Perhaps I misunderstood this comment then. I thought you had said the customer connected a diode between AVDD and DVDD such that the 3.3V DVDD supply voltage was indirectly powering AVDD. Therefore, I thought it was well understood how AVDD was being powered. Were you actually saying that the customer believes that the ADS1230 has an internal protection diode that is somehow powering AVDD through DVDD?

    There are definitely instances in some ADCs where powering DVDD can backfeed into other areas of the die and indirectly provide power to another supply e.g. AVDD. However, this is not a good thing, and not a normal mode of operation. It is also possible that there are additional issues with the PCB routing and layout causing this phenomenon.

    Even if we could determine how AVDD was being powered in this case, we cannot provide the customer any guarantee, or even probability, of how the ADC will behave because this is an untested, unknown state with lots of variables. As you say, some of the boards might be working just fine, but there is no way to know how they will behave over time and temperature, as well as other many other factors. If the customer is willing to accept this risk, that is their choice.

    My recommendation would be to manually fix any boards that have already been produced such that the ADC is powered correctly.

    -Bryan

  • Hi Bryan,

    Thank you for your help.

    The customer feedback:

    I'm fully aware of the risk and I've instructed the production to implement a rework on the boards , nonetheless ,
    I'm not expecting from TI to take any guarantee , I'm just requesting , to get an insight about what may be causing this behavior

    Relating to the product behavior , so far we have produced a large number of boards and we have not encountered any apparent fault ,we've tested 23 boards between -40 to 80C , we've tested 10K boards @ 25C . we have 3 boards that are working at 25C for 1 week .

    Please check whether we can get an insight about what may be causing this behavior.

    Thanks.

    Best regards,

  • Hi Zhonghui,

    The customer did not really respond to my questions about the protection diode. Is that an external component, or are they assuming it is internal to the ADC?

    Can the customer send an accurate schematic showing how the board is designed, including the error (where AVDD is not connected)?

    -Bryan

  • Hi Bryan,

    Thank you for your help.

    I sent you the circuit diagram and other information by email. Please help me analyze it.

    Thank you in advance.


    Best regards,

  • Hi Zhonghui,

    Thanks, I will discuss this with you offline then

    -Bryan