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LM95071: Large reading error at specific temperature

Derrick W
Prodigy 30 points
Part Number: LM95071

We are interfacing to a LM95071 with a PIC16F818 using bit-bashed SPI. We have noticed that whenever the device is tested in the ESS chamber, there is a specific temperature that will show very poor accuracy. Here's a graph of one device tested over a 12 hour period. The LM95071 is sampled once per second, and generally the accuracy is quite good. However you can see that at approximately 53 Celsius, there is a large error of about +-8 degrees.

The temperature at which this error occurs varies by individual IC.

We are powering our LM95071s from 5V DC. I have confirmed that there is very little ripple (< 50mV) on this supply when the error is occurring. I have also confirmed our bit bashed SPI from the PIC is not exceeding any of the LM95071's serial timing parameters, and it looks fine.

Does anyone have any hints as to what could be going on here?

  • 0
    TI__Mastermind 31600 points
    Hi Derrick,

    Thank you for reaching out to us. Could you please do a test for me by stressing the power supply to 6V? Afterward, please redo your test again if you see the same issue again.

    Aaron
  • 0 in reply to Aaron Heng
    Prodigy 30 points
    Hi Aaron, thanks for the response.
    I will test this and get back to you; there are other devices on the 5V rail that won't tolerate 6V, so we'll have to isolate the LM95071's supply.
  • 0 in reply to Derrick W
    Prodigy 30 points
    I isolated the power supply on the LM95071 and ran it from an adjustable bench supply at both 6V and 5V. In both cases, the error was no longer present, so this must be an issue with the supply voltage.

    We re-connected the LM95071 to our board's 5V rail, then re-tested in the ESS chamber with extra 10nF and 1000nF bypass capacitors, in addition to the 100nF that was already present. This also removed the error. We will re-test with only the 1000nF bypass cap connected tonight to confirm that this resolves the issue.