Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

  • State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 31 subscribers
  • Views 551 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.

LM95214: LM95214

go chee wan
Prodigy 50 points
Part Number: LM95214

Hi,

Would like to ask about how to design  the diode at FPGA.

What voltage should I assumed for D+ and D-.

  • 0
    TI__Mastermind 28070 points

    Hello Go Chee Wan,

    For almost all of our remote temperature sensors, including the LM95214, we recommend members of the 3904 (NPN) or 3906 (PNP) transistor families based on their electrical parameters. The LM95214 datasheet doesn't go into details, but the below summary taken from the datasheet for the TMP423 explains what parameters are important when selecting a diode to be measured. Keep in mind that the most significant factor in determining accuracy for the measured diode though is the n-factor value, which for the LM95214 is ideally 1.003.

    Please let me know if you have any other questions.

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    Prodigy 50 points
    Sorry. Mine one is inside the ic. Not outside.
  • 0 in reply to go chee wan
    TI__Mastermind 28070 points

    Hello Go Chee Wan,

    I see, you should know that there is a fairly good range of diodes that will work with the LM95214. The LM95214 will work by forcing current into the diode that you want to use, and then measuring the VBE value that results.

    You need to design a diode-connected bipolar junction transistor, that will have VBE values that are within reasonable bounds in the worst cases. Based on the datasheet the worst cases for the LM95214 are: 

    1. 10µA (typical minimum) biasing current from the LM95214 at the highest temperature you expect the FPGA to operate at. (Lowest VBE)
    2. 230µA (absolute Max) biasing current from the LM95214 at the lowest temperature you expect the FPGA to operate at.  (Highest  VBE)

    The 0.25V to 0.95V is just a safe voltage range we recommend. If your transistor falls within that range it should work with the LM95214. 

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    Prodigy 50 points

    Hi Brandon fisher,

    Mean vbe fall between 0.25v to 0.95v will be fine
    by meet the current range and temp above?

  • 0 in reply to Brandon Fisher94
    Prodigy 50 points

    Hi Brandon Fisher,

    For accurately forecast the performance of the IC.

    Could you provide us with  reasonable package and board resistance?

    I think I can get the package RLC from ibis model of LM95214,

    but how about board resistance?

  • 0 in reply to go chee wan
    TI__Mastermind 28070 points
    Hello Go Chee Wan,

    When we validate the performance of these parts we do so in package, so the device will meet the specification without considering package RLC effects. For simulation purposes you can definitely use the values in the IBIS model.

    By board resistance, do you mean the resistance of the traces?

    The trace resistance will depend on how far the diode you are measuring is from the LM95214, the trace width, copper thickness, and trace shape. Its a hard quantity to guess at. If you have an idea of what the width, length, and thickness of the copper traces would be it would be possible to give a pretty good estimate. For reference, an 8-10 mil trace, which is 10in long, will give around 1 Ohm of trace resistance on 0.5 oz copper.

    Best Regards,
    Brandon Fisher
  • 0 in reply to Brandon Fisher94
    Prodigy 50 points
    hi Brandon Fisher,
    Thanks a lot.