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TPS73801: Thermal Limit

T Kishi
Genius 4425 points
Part Number: TPS73801

Hi

My Customer has question.

I'd like to confirm this matter as soon as it is in a hurry.Please cooperate me.

TPS73801 overcurrent protection is recognized as a foldback method.
Also, in this state, it recognizes that Thermal Protection works when the temperature of Device rises.
What is the temperature threshold at which Thermal Protection works?
Also, how much recover temperature?

Best Regard

T Kishi

  • 0
    Guru 140200 points

    Hi T,

    there's no simple protection scheme in the TPS73801. It's more a complex SOA protection which depends not only on temperature, but also on load current and input to output differential voltage. Please have a look at figure 14 of datasheet:

    Datasheet also mentions, that the recommended maximum operating junction temperature is 125°C. So, the temperature shutdown will take place at a temperature above 125°C. But there's also manufacturing tolerances so that a sharp turn-on or turn-off threshold temperature for the thermal shutdown cannot be given.

    Allthough the datasheet specifies the maximum operating junction temperature as 125°C it's not recommended to run the regulator for long periods at such high temperatures because the life time can decrease. It's always wise to keep the junction temperature at a minimum by including enough headroom. The thermal shutdown should never be a substitute for a proper thermal design. It's like with the fire distinguisher: You want to have it, but you don't want to ever use it... :-)

    Kai

  • 0 in reply to kai klaas69
    Genius 4425 points
    Hi Kai

    Thank you for reply.

    Thermal design is not performed by the value of Thermal Shutdown.

    What customers are concerned about when the temperature rises in case of　abnormality, the IC is worried about how much overheating protection works at the IC.

    Is there no definite Thermal Shutdown threshold for TPS 73801?

    Best Regard
    T Kishi
  • 0 in reply to T Kishi
    TI__Mastermind 23361 points
    Hi T,

    Like Kai suggested, unfortunately there are no typical temperature available for the entering of the thermal limiting or recovering from thermal limiting. The device does have thermal limiting protection.

    Regards,
    Jason Song
  • 0 in reply to Jason Song
    Genius 4425 points
    Hi Jason

    Thank you for reply.

    I confirmed Figure 14 that Kai posted.
    Customers use @ VIN = 12V.
    In this case, when the load is short-circuited, it seems to flow as much as 1.5 A (TA = 125 ° C.)Is it correct in understanding that such current does not actually flow?

    When VIN = 12 V, what is the LDO loss when the load is short-circuited?

    Best Regard
    T Kishi
  • 0 in reply to T Kishi
    Guru 140200 points
    Hi T,

    in a short circuit event when the output voltage becomes 0V, the input to output differential voltage will be 12V. According to figure 14 a short circuit current of 0.9A...1.5A will typically flow, depending on temperature. Assume it is 1.3A at 25°C temperature, then 15.6W will have to be dissipated in the TPS73801 for a short moment. This will make the chip heat up, of course, and within a fraction of second the short circuit current will decrease according to figure 14. At this moment the heat dissipation will also decrease because of the decreased short circuit current. If the TPS73801 cannot totally remove the heat, the regulator will heat up more and more up to the moment when the temperature shutdown takes place

    So, yes, the 1.5A can actually flow in a short circuit event, at least briefly.

    Kai
  • 0 in reply to kai klaas69
    Genius 4425 points
    Hi Kai

    TPS73801 does not have a definite Thermal Shutdown threshold,but will the Thermal Shutdown occur as the fever rises?
    Or is it the same meaning as "thermal limiting protection" Jason says?

    Best Regard
    T Kishi
  • 0 in reply to T Kishi
    TI__Expert 4435 points
    Hi T,

    Thermal shutdown and thermal limiting protection refer to the same protection mechanism in the linear regulator.
  • 0 in reply to Eric.Preiss
    Genius 4425 points
    Hi Eric kai

    Thank you for reply.

    How much loss will occur in TPS 73801 when Short is done at input 12 V?
    Or, to what extent does the temperature of TPS 73801 rise? Is it 125 ℃?

    Best Regard
    T Kishi
  • 0 in reply to T Kishi
    Guru 140200 points
    Hi T,

    from figure 14 you can see that at 125° about 1A can flow. This gives a heat dissipation of 12W. With a thermal resistance of 51°C/W the junction temperature would theoretically rise to 12W x 51°C/W = 612°C above ambient temperature. This will not happen, of course, because the thermal shut down will turn-off the chip much earlier. But, yes, the chip will heavily heat up and will reach a temperarure of more than 125°.

    See also section 10.3 of datasheet.

    Kai
  • 0 in reply to kai klaas69
    Genius 4425 points
    Hi kai

    Is the temperature of TPS73801 rising at short circuit and TPS73801 Tj exceeds 125°C even if the current decreases at thermal shutdown?
    If that is true, even if the temperature exceeds 125 °C during short circuit, is TPS 73801 OK?

    Best Regard
    T Kishi
  • 0 in reply to T Kishi
    TI__Mastermind 23361 points
    Hi Kishi,

    At short circuit, the temperature will keep increasing with current flowing until thermal shutdown kicks in, once the device is in thermal shutdown, current flow will be stopped and temperature will decrease.

    TPS73801 has been designed and tested to run under 125C Tj and continuously running the device above the recommended temperature will degrade the reliability of the device.

    Regards,
    Jason Song