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Understanding possible damage to LM35?

Edm
Prodigy 30 points
Other Parts Discussed in Thread: LM35

Recently, i encountered damage to our LM35 temp sensor assembly on one of our applications. The temp sensor assembly caught fire when one of our high power bulb (36V 400W) arch to the case. I do not know if this was an instantaneous event that happen or a slow build up overtime (for example LM35 part heating up). The temp sensor assembly has the following components in it;  LM35DT TO220-3, 2 capacitors for decoupling, cable wires, DP270 epoxy, 4-40 1/8 fastener, and an aluminum block for housing all of the parts in it.

The tab of the LM35 is fastened to the temp sensor aluminum block which is fastened to the lamp block assembly. My question is if anyone has thoughts as to how did this happen? The bulb showed no sign of damage

Thanks

  • TI__Expert 7220 points
    Hi Edm,

    The arcing from the high power bulb may have exceeded the absolute max ratings of the LM35 which caused some kind of damage to the part. We only guarantee the LM35 to work under the absolute max ratings but we can perform some failure analysis of the part if it is still viable.

    -Michael Wong
  • in reply to Michael Wong
    Prodigy 30 points
    Thanks Michael for the response. With the arching the LM35 could have been exposed to 36V temporary on tab. Do you think isolating the tab of the LM35 with a thermal pad could help prevent this issue from happening? Also any other suggestion to improve robustness of design is appreciated. I still have the part if you are interested although it is buried in epoxy
  • in reply to Edm
    TI__Expert 7220 points
    Hi Edm,

    Yes, some isolation like a thermal interface material (TIM) will help. TIMs come in all sorts of varieties and ratings so pick one that is best suited for your application.

    Please email me at michael.wong@ti.com for shipping details.

    -Michael Wong