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INA128: Change to "Input Protection Circuit"?

Daren Jones
Prodigy 10 points
Part Number: INA128

Tool/software:

We have been using INA128s in one of our low volume products for more than ten years without any problems. 

However, in our latest batch of boards we are having issues which are pointing at the INA128.

Our application is a test system and we use the INA 128 (G=50) to look for a small signal on one of the UUT outputs at times when the output is off. We also apply various switched loads to this output and use another INA to measure the UUT output when on and loaded.

As part of our system's selftest regime, a 100mA constant current continuity test (supplied at 28V) is used to test the values of the load resistors. On our latest batches of systems, these tests are failing with low resistance results, suggesting a parallel path through the INA128.

Looking back at the datasheet I used when I originally designed our circuit reveals the following Input Protection characteristics:

In the latest version of the INA128 datasheet is the following which suggests that the input protection has changed significantly.

Can you please confirm that I am correct, advise on when this change occurred and also advise on an alternative to the INA128 that has the old input protection characteristics?

Many thanks

Daren

  • 0
    Guru 288480 points

    The new die revision was announced in PCN 20220802000.1.

    The input current under overvoltage conditions is not one of the guaranteed parameters.

    Is your current larger than the 6 mA shown in figure 7-10?

  • 0
    TI__Mastermind 23650 points

    Hi Daren, 

    As Clemens pointed out the product change notification was sent out on August 03, 2022 discussing the qualification of a new fab & process technology (FFAB, BICOM3XHV) die revision, and Assembly & BOM option. Let us know if we can be of further assistance.

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 10 points

    Chris,

    Thanks for your reply.

    I am struggling to understand how such a significant change to the device's input protection circuits can be declared as having no effect on the form, fit or function of the device.

    Is there any marking on the device to indicate it's a new version? How could a distributor know an old from a new?

    Do any of your distributors have stock of old versions?

    Kindest Regards

    Daren

  • 0 in reply to Daren Jones
    Guru 288480 points

    The fab and assembly locations are shown on the shipping label, but there is no publicly available information on the chip itself.

    When buying, it is not possible to choose a fab. (And the old one is being phased out.)

    As far as I can see, your only choice is to change the test to account for the larger leakage current.

  • 0 in reply to Daren Jones
    TI__Mastermind 23650 points

    Hi Daren, 

    Clemens is correct. The device has moved to a new fab and the only devices that will be available in the future are from the new fab. Unfortunately there is no way to specifically order the old device. 

    -Chris Featherstone

  • 0 in reply to Chris Featherstone
    TI__Genius 12795 points

    Hi Daren,

    For the most part, devices from the new fab. have improved performance.  However due to differences in process, to achieve the same specs. within the EC table (i.e. offset, IB, Gain, etc.) we aren't able to match the exact performance of the protection circuit.  For most solutions, the parametric performance of the protection circuit isn't critical, as long as it accomplishes the goal of protection.  It is unfortunate this is a tested parameter for you, but I believe you will find the operation within the linear region is the same but with lower current consumption (Iq).

    Regards,
    Mike