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UA723: Problem with regulation waaay out of spec!

PHILIP STARBUCK
Prodigy 15 points
Part Number: UA723

I have used 723 (mostly T-100 and PDIP) parts in instrumentation systems and production designs for may years.  In 2012 I used the part in two new designs.  we completed out preliminary design validation process using PDIP pars successfully and transitioned to uA723C parts for production.  Unfortunately we were never able to obtain satisfactory voltage regulation that was well beyond the spec sheet parameters (10's of mV drift) and had to abandon the design and move on another design.  We opened a dialog with TI to try to root cause the problem, however it apparently wend down the rabbit hole and we had to move on without a resolution.  We now have a project that I would like to use the part in (it really can be a great part for our applications) but before we commit to it again I would like to find out if we had a bad lot of parts or the die has changed to the point where it is not compatible with our baseline design.  I did notice that one of the app notes recommended a n external voltage reference in order to improve regulation, perhaps this is an indication of a problem and we can certainly add that reference if necessary.  Unfortunately because of the nature of our business I cannot post a schematic here but would like to have a response and share a schematic directly with one of your product engineers off line and hopefully resolve this issue before we move on to another part again.

  • 0
    TI__Genius 13115 points
    Hi Phillip,

    I've sent you an E2E friend request so we can exchange email addresses without them being available to the rest of the public forum.

    -Kyle
  • 0
    TI__Genius 13115 points

    For documentation sake, I am posting what was learned and the mitigating steps that can be taken by the user in case anyone else comes across this issue in the future.

    Due to the process technology when this device was released (1972) some devices/lots exhibit signs of Zener Walkout which caused the output voltage to change over time (it can possibly take minutes for the output voltage to settle to it's final value). Zener Walkout occurs due to trapped charges during the fab process and will cause a Zener voltage to change and since a Zener is used to create the voltage that the output voltage is referenced to you see a corresponding change in the output voltage. The unfortunate part about this is that it can take minutes for a device to settle while the production tests that a device are significantly shorter so these types of failures cannot be screened out. Since the number/amount of trapped charge is variable due to normal process variations it may not be seen on every lot which explains why your old unit’s/designs didn’t exhibit the problem in the same circuit.

    Knowing all of that but not knowing the scale of the number of devices you’ll be producing I see three potential work arounds for you

    1. Screen units by testing the output over time to see if they change, if they don’t change then they are production worthy and use accordingly (obviously this is only feasible for small scale)
    2. Burn in units at high temp to move the trapped charges. This should yield a higher percentage of usable parts.
    3. Migrate the design to a new device.
      1. If you provide us with the design specs for this power solution and we may be able to find a newer device that is run on a much more modern fab process or one that doesn’t use this topology of using a Zener to create the reference voltage.