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TPS7A49: Operating virtual junction

T Kishi
Genius 4425 points

Part Number: TPS7A49
Other Parts Discussed in Thread: TPS74401

Hi

My Customer has question.

Although "Operating virtual junction (Tj)" described in "Absolute Maximum Ratings" of TPS7A49 is 125°C.,

the allowable temperature is lower than that of the device described as Tj = 150°C.

Is not it? Or will not it change?


What is "Operating virtual junction"?
Is there any difference between "Operating junction temperature"?

Best Regard

T Kishi

  • 0
    Guru 140200 points
    Hi Kishi,

    the term "operating virtual junction" is taken from the IEC standards. Here it means the same as "operating junction temperature", which is the temperature of the silicon die.

    The recommended maximum operating junction temperature of the TPS7A49 is 125°C. This is also the absolute maximum rating. So, do not exceed this die temperature in operation.

    Of course, 125°C is not the junction temperature where the die becomes suddenly damaged. This begins above 150°C. But lifetime of a silicon chip depends on chip temperature and decreases exponentially with temperature. -> Arrhenius equation. So, it's not wise to run the chip for a long periode at 125°C or even above.

    Kai
  • 0 in reply to kai klaas69
    TI__Expert 7035 points
    Hi Kishi,

    Kai is correct the "operating virtual junction" will be the same as operating junction temperature. And as the part is heating up the lifetime degrades according to the arrhenius equation.

    When you are designing the LDO you should take care to limit the junction temperature to within our operating range -40C to 125C. You can use the Theta JA numbers and the power dissipation to make sure that you are not exceeding the maximum junction temperature for the LDO.

    Regards,
    Mark
  • 0 in reply to Mark Sellers
    Genius 4425 points

    Hi Kai & Mark

    Thank you for reply.

    I realized that TPS7A49 was actually designed in the same way as Device with　Maximum Rating = 150℃
    (Tj must be less than 125°C.)

    As one confirmation, is the maximum rating of TPS7A49 actually 150°C correct?
    Just is not the data sheet changed?
    TPS74401 has revised datasheet and has changed from maximum rating = 125 ° C to 150 ° C. (Rev M ⇒ Rev N)
    I want to check whether the device whose maximum rating is 125 ° C, such as TPS7A49, is similar to TPS74401.

    Best Regard

    T Kishi

  • 0 in reply to T Kishi
    TI__Expert 7035 points
    Hi T Kishi,

    The datasheet for the TPS7A49 is correct with the abs max rating of 125C, there are no plans currently to increase the abs max junction temperature.

    The maximum junction temperature for the TPS7A49 is 125C. When designing with this part the thermal calculations should be done to keep this part under that temperature. However, if the junction temperature exceeds 125C like in the case of thermal shutdown the device will not immediately break it will simply degrade device lifetime.

    Regards,
    Mark
  • 0 in reply to T Kishi
    Guru 140200 points
    Hi Kishi,

    you wrote: "TPS74401 has revised datasheet and has changed from maximum rating = 125 ° C to 150 ° C"

    Nevertheless, the "recommended operation conditions" of datasheet mentions a maximum Tj of 125°C.

    Kishi, it's not wise to operate a silicon chip at such high temperatures. For a longlife application a Tj of 80°C, maximum 100°C is acceptable. But die temperatures beyond will exponentially decrease the lifetime of chip! Please have a look at the Arrhenius quation stuff.

    Kai