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Problems with LM95172 at 190C

1898541
Expert 1105 points

Hi,

LM95172 is a 200C sensor. We are testing it till 190C. Normally when powered up it works well till 190C most of the time. But if we power cycle at 190C the IC stops working. It's connected on a SPI bus. We monitored the SPI bus to see we stopped receiving data when we power cycle the chip at 190C. Once the temperature is lowered to 180C the chip starts responding again with data. 

Can you please let us know if this is a known issue or we suppose to do something we are not doing right. 

Thanks, 

AQ

  • 0
    TI__Mastermind 37370 points

    Hi AQ,

    I will look into this, and get back to you soon.

    Aaron

  • 0
    TI__Mastermind 37370 points

    Hi AQ,

    It seem that I got the internal email similar to this post. Could you provide me the following question?

    1. Can you give us a scope shot of the supply after power cycling? We want to see its behavior when the temp sensor is not responding. 
    2. Also, can you give us a scope shot of the interface at the time when lm95172 begins responding at 195C?
    3. Are you ok sharing the schematic as well? We want to make sure nothing in the design looks suspicious?
    4. How do you test LM95172? Did you have the part itself in the oven?

    Aaron

  • 0 in reply to Aaron Heng
    Expert 1105 points

    Thanks Aaron Heng for the reply, 

    I am attaching the required screenshots here. 

    We test it on our PCB board. We put the complete board into the oven and heat it to ~190C. 

    #1 - Working at 190C

    #2 - Working at 190C

    #3 - Power cycled at 190C

    #4 - Not working at 190C (after power cycle)

    #5 - Not working at 190C

    Hope this information is enough for you. 

    Thanks, 

    AQ

  • 0 in reply to 1898541
    TI__Mastermind 37370 points

    Hi AQ,

    I want to inform you that I am still working on your issue. I am trying to duplicate your setup to see if this occurs on my side. Also, when you powered cycle the device, did you follow the power-up sequence on page 8 and 9 of the datasheet?

    Aaron

  • 0 in reply to Aaron Heng
    Expert 1105 points

    Hi Aaron,

    - Our Vdd and Vio are the same, so no lag between them. 

    - Our power up ramp is very steep and we come to  power in less than 5ms

    Is there any other concern you may have ? The software reset scheme also is implemented. 

  • 0 in reply to 1898541
    TI__Mastermind 37370 points

    Hi AQ,

    Thank you for providing the snapshot, and I would like to inform you that I am still working on your issue. We never face this issue before, and I am stuck right now.  We might need your help to get a better understand on your end. Could you provide me a complete waveform of the SPI communication? On your snapshot #5, could you please zoom in when the CS takes “LOW”? I would like to see if there is a pulse on the data line.

    I tried to duplicate your setup. The only difference between yours and mine setup is that I inserted the LM95172 and bypass caps inside the oven not a complete board setup.  Since you placed your board inside the oven, could you make sure that your discrete components can handle at high temperature?

    Here are some of my snapshot pictures.

    Channel 1 => CS

    Channel 2 => SCLK

    Channel 3 => SIO

    Channel 4 => Vdd

     

    Vdd Ramp Rate at 190°C. I noticed that your Vdd ramp rate seem to be brutal.

     

    I turned power off and on at 190°C, and it was still working. If you look at the first 16-bit, the temperature turned out to be 194°C. I even ramped up to 197°C, and nothing seems to be suspicious.

    When you give me a complete waveform of the SPI communication, I will try to generate a similar waveform to see anything comes up.

    Aaron