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AD5420 Output range shifts up by tens to hundreds of milliAmps

We occasionally experience a failure of the AD5420 where the output
will shift up tens to hundreds of milliAmps (or more). This failure
occurs after our product is Hi-Pot tested. Our Hi-Pot test is one
minute of 500 VAC between the analog output and the chassis connection
and 1500 VAC between the power lines and chassis connection. Our product is powered through a transformer.

For example, one AD5420 was calibrated to a normal 4-20mA
output. After Hi-Pot testing, the data-word that produces a 4 mA
output, now produces a 25 mA output. Likewise the data-word that
normally produces a 20 mA output produces a 134 mA output.  This is a
permanent condition after Hi-Pot: regardless of the number of power
cycles, the abnormal 25mA to 134mA output swing remains.

I have verified that there is no difference in the serial bus signal
levels, timing or data/control register values before and after this
Hi-pot induced condition appears.

Note that I have discovered a brute force way of correcting the issue:
I briefly touched the R3sense output (TSSOP Pin 18) to ground. This
causes AVDD to collapse and the product microprocessor to reset.

Upon resetting, to output signal swing was restored to the normal 4mA to
20mA range.

I've applied this brute force fix to 5 different defective units, and
have cleared up the problem each time.

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  • Hi Tom

    Apologies. I meant 0x56 for the reset command.

    We still want you to send the units for analysis as it seems to be that you have done the necessary steps to ensure the internal calibration registers are read correctly during power-up. We understand that the high temperature during demounting could cause a different failure but that should be identified during the analysis.

    Best regards,

    Rainier

  • Hello: I am re-opening this thread almost 2 years later, because back in 2018, we were planning to replace the AD5420 with the old AD420.  This plan was cancelled.  In the meantime, the problems with the AD5420 seemed to abate. We attributed this to a change in the die that fixed the problem.

    Now the problem is back. We are interested in sending you defective AD5420's for analysis. Could you please give me the shipping information ? Thank You.

  • Hi Tom,

    Have you noticed in specific pattern where the problem occurs on certain date codes only?

    Kindly contact the distributor where you purchased the part.

    Cheers,

    Ivan

  • The problem is persistent. There is no known "pattern" that triggers the problem.  I just evaluated two problem units with a date code of 1921 and 1922.  Here is the list of problem AD5420 part date codes that are in our system:  1644, 1648,1730, 1734,1749,1742.

  • Hi Tom,

    I read back the previous conversations in this post. Would like to ask if you ever tried monitoring the pins of the device especially the supplies during the hipot testing. Would like to know if the ABS MAX ratings of the device was violated.

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