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LM22674: thermische Betrachtung LM22674

Michael Ungerer
Prodigy 160 points
Part Number: LM22674
Other Parts Discussed in Thread: TPS54040

Ich verwende den Spannugsregler LM22674MR-5.0/NOPB.

Die LP auf der dieser Regler montiert ist habe ich nun ins passende Gehäuse eingebaut und voll belastet bei einer Umgebungstemperatur von 60°C betrieben.

Um zu sehen wie warm der Regler wird, habe ich auf diesen ein Thermoelement geklebt um die Gehäuseoberflächentemperatur zu messen...diese liegt bei ca. 115°C.

Jetzt ist meine Frage wie Ich überprüfen kann ob die Temperatur für das Bauteil noch in Ordnung ist.

Der LM22674 Typ hat eine max. Junction Temperatur von 125°C

Leider weiß Ich jetzt nicht wie Ich überprüfen kann ob die Temperatur von 115°C noch in Ordnung geht oder ob der baustein dadurch beschädigt wird!?

Im Datenblatt fehlt auch jegliche Angabe zu den thermischen Widerständen.

Ich hoffe Sie können mir hier weiterhelfen.

  • 0
    TI__Mastermind 25590 points
    Michael,

    I apologize I'll only be able to reply in English.

    115C is warm but it's 10C below the recommended operating temp of 125 max (150abs max). Elevated temperature will reduce the lifetime of the IC but we do not have solid data to give exact numbers.

    The datasheet has RθJA = 60C/W but this is not very helpful since most of the heat will dissipate through the board. You can expect the best thermal performance if you have a large solid GND plane connected to the thermal pad of the IC.

    -Sam
  • 0 in reply to Samuel Jaffe
    Prodigy 160 points
    Hi Sam,

    sorry but i have one more question.
    You said that my 115C are ok because it`s 10C below the 125C.
    But i think that two temperature are comletly different.
    My 110C ist the case temperature and the 125C in the datasheet is the junction temperature, so i can`t compare these temperatures together!?
    So i need an information how to compare these two temperature together...and i think this will only be possible with the thermal resistance junction to case!?

    Michael
  • 0 in reply to Michael Ungerer
    TI__Mastermind 25590 points

    Michael,

    You are correct! Sorry for my misunderstanding. Yes, an increase in IC temp of more than 15 degrees from 110C ambient will be too hot.

    Let me see if I can get the junction to case spec for you.

    In the meantime check out WEBENCH (LM22674 product page on the right, scroll down a bit). You can run thermal simulations with a design from your specs. This will probably be more accurate since thermals are heavily layout dependent.

    -Sam

  • 0 in reply to Samuel Jaffe
    TI__Mastermind 25590 points

    Michael,

    I've confirmed that we do not have the data for junction to case. You can use WEBENCH or you can order an EVM and check the temp at your conditions.

    You could also look at the thermal specs for TPS54040. This part is similar and has all the typical thermal specs in the datasheet with a similar theta JA as LM22674.

    -Sam