• State TI Thinks Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 1038 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMT87: About Accuracy

Jake Jung
Expert 1915 points
Part Number: LMT87

Hi Tiers.

My customer using LMT87.

But Vout is not correct.

For Example, When ambient air temperature is 26~27 degree, Vout is 2.27~2.28V in datasheet table.

But measured Vout voltage is 2.21V

Why it is not correct?

And How can debug this?

VDD is 5V.

VDD bypass capacitor is 0.1uF.

No Vout filter.

Please let me know.

  • 0
    TI__Mastermind 35895 points
    Hi Jung,

    Thank you for your question. A TI representative will get back to you tomorrow, as today is a holiday.

    Thanks for your understanding,
    Ren
  • 0
    TI__Genius 12780 points

    Hi SS Jung,

    What is the load on Vout?

    Best Regards,

    Dan

  • 0 in reply to dBrock
    TI__Expert 6475 points
    Jung,

    How are you measuring the output?
    Will you have a different measurement if you add an output cap (e.g. 10nF)?
    Is this repeatable with multiple devices?
    Have you used LMT87 before?

    -Kelvin
  • 0 in reply to dBrock
    Expert 1915 points
    Hi Daniel.

    No load.
    Vout is not connect anyload. Floating.
  • 0 in reply to Kelvin Le THS
    Expert 1915 points
    Hi Kelvin.

    1. They measuring with Multimeter.
    2. Vout filter (R and C) is not used. But, When using 1KOhm and 1uF RC filter, Vout is almost same.
    3. No.
    4. Yes. The customer using in another device. But this symptom is same. So, They using some offset.
    In this case, they designed LMT87 in new project. And they want to know why this symptom is occurred.
  • 0 in reply to Jake Jung
    TI__Expert 6475 points
    Jung,

    You said that this issue is not repeatable with multiple devices (3) but the next answer (4) you said that they are having the same issue in another device?

    Please clarify the statistics of this issue? (1/5 devices show a large offset)

    What end equipment are they using LMT87 for? What device package are we talking about?

    -Kelvin
  • 0 in reply to Kelvin Le THS
    Expert 1915 points

    They are using LMT87 in A and B devices as same schematics.

    A device is old model and B device is new.

    This accuracy issue is same.

    End application is GAS Detector and package is DCK Package.

    Schematic is below.

    And they tested in removing R32 and C9, Just only LMT87.

    In Ambient temp 26~27 degree, Vout is 2.21V. But in datasheet 2.28~2.27V at 26~27 degree.

    How can improve accuracy?

  • 0 in reply to Jake Jung
    TI__Expert 6475 points
    Jung,

    1. Please confirm that this offset is reproducible for 5 devices
    2. Please confirm the DMM is accurate by measuring a known voltage source
    3. What is the temperature reference probe accuracy?
    4. How close is this temperature probe to the LMT87? I want to make sure that there isn't a local temperature gradient where the local temperature close to LMT87 is higher than the surrounding ambient air.

    You mentioned that LMT87 outputs 2.21V without any load. This implies a ~31.5C reading. If the local ambient air close to the LMT87 is 27C, we expect a worst case reading of 27C+2.7C of 29.7C. But this assume that the local air is actually 27C.

    -Kelvin