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UC2875: DWP Package: Slope Pin 26

Brandon Orellana
Prodigy 10 points
Part Number: UC2875

Tool/software:

Hello,

I have a question regarding UC2875DWP.

Typically I was measuring ~231kΩ between SLOPE pin 26 and GND pin 28. However, I recently measured a value of ~207kΩ, about a 10% difference.

Requesting for the tolerance of SLOPE pin 26 for this component.

Thank you.

  • 0
    TI__Genius 12795 points

    Did you measure the resistance between two pins without powering IC? Why is the resistance important? It is not a datasheet parameter.

    We will get back to you on the tolerance soon.

  • 0 in reply to Ning Tan
    TI__Genius 12795 points

    Can you clarify the test condition? what is the voltage you are forcing when measure the resistance?

  • 0 in reply to Ning Tan
    TI__Genius 12795 points

    Please also share the LTC with us so we can look into this in detail. We need both 230k and 207k samples

  • 0 in reply to Ning Tan
    Prodigy 10 points

    The resistance was measured without powering the IC.

    The resistance value is important as this simple check has indicated a pass or fail with our internal testing.

  • 0 in reply to Ning Tan
    Prodigy 10 points

    The 230k LTC was 47Z228V and the 207k was 37Z17RV.

  • 0 in reply to Brandon Orellana
    TI__Genius 12795 points

    what is the test condition? can you share?

  • 0 in reply to Ning Tan
    Prodigy 10 points

    There is a 174k pull up resistor connected between pin 26 and pin 15 of the IC. The pull up resistor measures ~8% lower than expected. It was confirmed that the resistor itself is not an issue.

  • 0 in reply to Brandon Orellana
    TI__Genius 12795 points

    Can you share the bias condition when you measure the resistance? are you using multimeter to measure the resistance between pin 26 and GND, which means the voltage on pin26 is unknown? pin15 is Vin. I thought Vin is not powered. Why would that pull up resistor impact the resistance between pin 26 and GND?

  • 0 in reply to Ning Tan
    Prodigy 10 points

    Yes, the resistance value was measured using a multimeter with + on pin 26. The value of the pull up resistor does not impact the resistance between pin 26 and GND. For a bit more context, we measure the pull up resistor (~174k). When UC2875DWP LTC 47Z228V is installed, the pull up resistor reads ~174k (pass). When LTC 37Z17RV is installed the pull up resistor reads ~8% less ("fail"). Taking a look at UC2875DWP, it was noticed that when the test "failed" it had a lower reading between pin 26 and GND, swapping the IC caused the resistor to read ~174k. The thought was there might be some variance on the input of pin 26, but are unsure what is an allowable variance/tolerance.

  • 0 in reply to Brandon Orellana
    TI__Mastermind 40340 points

    Hello Brandon, 

    The datasheet figure on page 11 shows that the circuit attached to pin 26 is a current mirror structure which has characteristics similar to that of a diode to GND.  Actually, in this case, two diodes in parallel to GND.  They cannot be treated as resistances despite the apparent test "success" in previous batches. 
    The diode forward "resistance' is highly non-linear, can vary from lot to lot, and is also temperature dependent. 

    I recommend that you significantly widen you pass/fail criteria for the resistance on pin 26 to GND, or change the test to a diode test. 
    There is nothing wrong with LTC 37Z17RV, except for the test itself. 

    Regards,
    Ulrich