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SN751178: Causes of thermal shutdown and recovery

Okutsu
Prodigy 180 points
Part Number: SN751178

Hi, TEAM.

Could you please continue to support the thread below?
e2e.ti.com/.../4843374 4843374


a. Please tell me the mechanism of thermal shutdown.
It seems that the IC does not have a thermocouple inside to detect it, so isn't overcurrent detection or overvoltage detection detected as thermal shutdown?

b. Once inside the company, we were unable to measure the temperature when the TXDB was not outputting (the same phenomenon as at the site was reproduced), and we have not repeated it since then.
However, when we assembled the same configuration and measured the temperature, the surface temperature of the parts was around 43°C.
I think it's hard to imagine a thermal shutdown at around 43℃,
Is it possible that the same event (such as thermal shutdown) could occur in other cases?
　
c. Also, is it possible that the manufacturing process of the SN751178NS has made thermal shutdown more likely to occur (for example, the surface of the package has become thinner)?
Although it has been changing the circuit, it did not occur in the old lot.

Thank you.

  • 0
    TI__Mastermind 46697 points

    Hi,

    So the original thread that is linked there wasn't an issue or damage detected - most likely too much power dissipated in the device. 

    a) Silicon has a temperature dependency - so you can relate temperature to voltage on silicon devices. I can't give too many details on how this achieved as that is our internal design - but the thermal shutdown is based on voltage sensing inside the device. 

    For b) and c):  

    1) IF the problem hasn't been seen again then it most likely isn't an IC problem but could be a testing problem - double check that because thermal shutdown is not a transient event. 

     2) We give absolutely no way to convert surface temperature to junction temperature - so making assumptions with this value is only wasting time - you need to measure power dissipated by device and ambient as that is the closest approximation you will be able to get with this device - and even then its a bad approximation because your system impacts the temperature rise in the part too so any number we give will be different then what you have in system. So you for answers you need to model the thermal behavior in your system - we can't do that for you. 

    3) This device has not changed since 1999.

    In conclusion:

    1. The problem hasn't reappeared - check your test conditions because most likely it is a tester error not a part error.

    2. Stop measuring surface temp when there is no way to convert it to junction temperature (something we actually specify) - essentially if we don't specify it, it is irrelevant. 

    Best,

    Parker Dodson