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DAC084S085: Output range mismatch

Giorgio Croci Candiani
Prodigy 20 points
Part Number: DAC084S085

Hi,

we recently bought a new reel of these ICs to be mounted on one of our products (which had already been in production for months).

On this new production run we had a very strange behaviour: the output range of the DAC seems to go from 2.5V to 5V instead of 0V-5V (Vref is obv 5V).

Everything else seems consistent: the input signals are clean and their values match the expected commands, output value has the correct % value within the range, the output has been also tested disconnecting the load. Anyway, nothing else has changed either in firmware or in hardware.

Do you have any suggestion on further tests or possible causes?

Thanks

  • 0
    TI__Genius 14220 points

    Hi Giorgio,

    Welcome to E2E and thank you for your query. In order to arrive at the root cause quickly, we can do the following test:

    A. Test the board with the new device (done and found a problem)

    B. Replace the device with a known-good old device, probably from another board

    A. Replace the known-good device with the currently non-working part again 

    If you can record the observations with the above A-B-A tests, we should be able to find the root cause. If you see that the new device has an issue, check multiple devices and we will know if this is a single device issue or an issue with the lot itself.

    Regards,

    Uttam Sahu

    Applications Engineer, Precision DAC

  • 0 in reply to Uttam Sahu
    Prodigy 20 points

    For the record, the problem has been solved.

    Turned out that the manufacturer of the boards had also sourced a new batch of input optocouplers, which had a different (higher) CTR category. The input signals had become sharper and faster, and we were able to notice that the first /SYNC edge was overlapping with the first 1->0 transition of the CLK, causing a spurious clock pulse to be counted.

    This was obviously a firmware bug; however it was remarkable how the behavior was very consistent on the two versions of the board (as far as we know, always working in the first version, always failing in the second one).

    Hope this report can be useful as a troubleshooting record case.

    Thanks & Regards