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ULQ2003A-Q1: Input Impedance

Part Number: ULQ2003A-Q1

My customer is testing the input impedance of the ULQ2003AQDRQ1. Here is his explanation:

According to the attached figure, the input impedance is nominally 12.9  Kohm (2.7K+7.2K+3K).  Recently our production units failed impedance tests where this device is a load on the signal under test. On removing the part, we measured the input on pins 1 thru 4 at 14.5Kohm each. We expect variations between lot date codes. We need to know the upper and lower limits of these variations so that we can adjust our test software accordingly to avoid false failures.  What is the TI manufacturing tolerances for the resistors in the ULQ2003AQDRQ1?

I sent him the minimum input impedance by using the Iin from the data sheet, but this does not imply what the maximum input impedance. Do we have these numbers? Is the number that they are using (14.5K) the proper number to use in their testing? Should they be using a higher number? Can we answer their questions?

Thanks for your help with this!

Richard Elmquist

  • Hello Richard,

    For these resistors, they don't have a very high accuracy as they are just biasing resistors. Typically the variation could be as high as 15%, so 14.5k would fall within that.

    Additionally, I believe there may be some offset from 12.9k as well, and I think it is typically on the higher end. I am not 100% sure what the offset from 12.9k might be, but if they are measuring a number of units, I would think they would get a pretty good idea of what a typical value is also. 

    Unfortunately, we don't have a specified maximum and minimum input resistance, but hopefully the above gives you a good enough idea. Let me know if you need more clarity on this or have additional questions.

    Best,
    Michael

  • Michael,

    Thanks for your response!

    I will let you know if the customer has any further questions.

    Thanks again

    Richard Elmquist