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LM117HVQML: LM117HVGW-QML thermal protection

Philippe PELEGRI
Prodigy 30 points
Part Number: LM117HVQML

Hi,

I'm using on a space application LM117HVGW-QML chips.

I need some information about internal thermal protection circuitry that is evoked in datasheet (SNVS357D– MARCH2006– REVISED APRIL2013).

* Which type of temperature limit is implemented (junction temp limit) ?

* Can we consider this protection will protect the chip from all defects (translated into thermal overheat): permanent or transient current overload will be fully covered by this protection and will avoid destruction or damage to the chip?

* What is the temperature trigger limit for the protection ?

* Is there an hysteresis system on the protection for desactivation?

* In the Note 2, below "Absolute Maximum ratings" table of the datasheet, "PFM" package is evoked. Is it equivalent to CFP GW package ?

* In Figure 5 of the datasheet, wich curve do I have to consider for the "CFP GW" package (there are only "T", "K" and "H" package codes on the Figure 5 curves) ?

Thanks for your help

Philippe

  • 0
    TI__Genius 17085 points

    Hello Philippe,

    The LM117HVGW uses the same die as the LM117HVH.  It has the 500 mA current limit and you should refer to the "H" version in the plots.

    The thermal shutdown typically kicks in when the junction temperature is around 165C but can vary from part to part.  It is not a sharp shutdown.  The supply voltage and output current slowly decrease as the temperature goes above the thermal shutdown point. 

    Since this is a space grade product, eveny units goes through burn-in for 240 hours at 125C before electrical test.  In addition, prior to burn-in, each unit goes through a short circuit test, where the output is shorted to ground through a 1 ohm resistor for 30 minutes to help screen out product defects.

    The GW package would be the same as PFM.

    Let me know if you have any other questions.

    Kirby

  • 0 in reply to Kirby Kruckmeyer96848
    Prodigy 30 points
    Hello Kirby,

    thank you for your reply.
    Just an additional question: do you know in which range the thermal shutdown trigger will be certified to be (varying from part to part) ?

    Philippe
  • 0 in reply to Philippe PELEGRI
    TI__Genius 17085 points

    We do not have characaterization data for the exact point where the thermal shutdown starts to become active other than to note that it will definitely be above 150C.

  • 0 in reply to Kirby Kruckmeyer96848
    Prodigy 30 points
    Hello Kirby,

    I don't understand why the protection trigger level is above the absolute maximum value of 150°C. I would deduct that despite of the thermal protection activation, the junction will be "damaged", because it will be over its safe operating range for a while. Am I right ?

    I need also some details about the behaviour of this protection once triggered: will it be "latched" until the current drops below the trigger level minus a delta value ? My exact wondering is about oscillating current waveform in presence of a permanent default: the protection should trigger, then deactivate when the junction temperature will have fallen below a secure value, then reactivate if the default is still present. This could lead to a sawtooth current waveform between "limitation current" and "zero current".
    You previously said that the protection is not "sharp shutdown" so I think the behaviour should be more like a "permanent high limit", leading to a dissipative effect as long as the default is present.
    Could you please detail the behaviour of the protection, especially around the trigger level ?

    Thanks
    Philippe
  • 0 in reply to Philippe PELEGRI
    TI__Genius 17085 points

    Hello Philippe,

    An excursion above 150C, hitting the thermal shutdown will not damage the part or impact its life.   Continuous operatioin above 150C could impact the life of the part.

    As I mentioned earlier, the thermal shutdown is a soft shutdown.   Once the thermal shutdown point is reached, the output voltage and current begin to decrease.   The output voltage and current will continue decrease as junction temperature rises.   Depending upon the application conditions and environment, the part could eventually reach a steady state.   Any sawtooth behavior on the output would be muted compared to a hard thermal shutdown.