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TPS785-Q1: Operating and Cutoff temp

May
Genius 9880 points
Part Number: TPS785-Q1
Other Parts Discussed in Thread: TPS7B82-Q1

Hi Team,

What is the correct operating temperature for this IC? In the first page of the datasheet it mention the operating temp is -40 to 125C while in page 33 the operating temp is -40 to 150C.

Also what is the minimum cutoff temperature? My customer application is oil and gas downhole. Minimum ambient operating temperature is 150 degC. They already qualify component to temperatures greater than their absolute maximum ratings. This is why they need to know the cutoff temp.

Thank you.

Regards,
May

  • 0
    TI__Expert 6825 points

    Hi May,

    There is no inconsistency here the different temperatures are talking about 2 different parameters ambient temperature and junction temperature. The required ambient temperature for a Grade 1 automotive part is 125C ambient, but because LDOs dissipate power we typically try to give a little more room in the operating junction temperature which is why that is up to 150C. 

    If they are using the part up to ambient temperatures up to 150C they will surely be beyond the absolute maximum junction temperature of 150C. 

    Regards,

    Mark

  • 0
    Prodigy 10 points

    Mark,

    There is an inconsistency in the TPS785-Q1 datasheet when page 1 states operating temp of +125 C Ta  (Tj = 150 degC) and the chart on page 33, column "Op Temp (degC)" is listed as -40 to 150.  "Op Temp" more than implies ambient operating temperature, and not junction temperature or that would have been stated as such, words matter.  This is not consistent specmanship.  

    We have used components rated at 125 degC and 150 degC in a gauge application for producing oil wells for more than 5 years after they were qualified at 160 degC.  We know that the regulator has a thermal cutoff near 162 degC ambient.  The gauge is relatively low power so the junction is higher than that but  thermal cutoff temp is not definitively known.  The ambient temp is the important part since we rate the gauges at 150 degC.

    The specific question that I need to be answered is what is the internal thermal cutoff design limit is for the TPS785-Q1.  I prefer a part that is rated for 150 ambient but that range is conspicuously missing from the families of LDO regulators thus far in my search.  The next temperature step up (with available inventory) is 210 degC, which is much higher and much more expensive than what is needed.  [edited to correct spelling] 

    Regards,

    Carl

  • 0 in reply to Carl Palmgren
    TI__Expert 6825 points

    HI Carl,

    I see what you are saying here, but the front page and the abs max tables are correct in this case. Where the ambient max is 125C Ta and TJ max is 150C. If you take the ambient temperature of this part above 125C you would have to have them do their own reliability calculations and qualifications.

    I am not sure what you mean by thermal cutoff design limit, but to get a part with 150C ambient rating you would have to use one of the 210C parts or the TPS7B82-Q1 or the TPS7A66H50-Q1 these are grade 0 parts that have a 150C ambient temperature rating. Some of the older Hi-rel parts spec a junction temperature of up to 150C, but I am pretty sure those are only referring to junction temp and not ambient temperature like all of the newer Q1 parts as well.

    Regards,

    Mark