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SN74ALVC164245: Maximum junction temperature

Markus Nabecker
Intellectual 260 points
Part Number: SN74ALVC164245
Other Parts Discussed in Thread: SN74LVC16T245-EP, SN74AVC16T245

Dear supoprt team!

In the datasheet of this component the operating free air temperature is defined from -40 to +85°C.

Additionally there is definition of the thremal resistance ( Rth(j-a) ) specified.

When I try to calculate the maximum power dissipation at a certain temperature i need the maximum junction temperature of the chip.

Pmax = ( Tj(max) - Ta(max) )  /  Rth(j-a)

Unfortunately there is no Tj(max) defined. I know that commonly the maximum junction temperature is 150°C.

But is this temperature also guaranteed from Texas Instruments and why didn't they mention it in the datasheet?

Kind regards,

Markus Nabecker

  • 0
    TI__Guru* 97046 points
    Hi Markus,
    In logic devices, it's unlikely that the limiting factor for operation will be Tj(max). The value is equal to the maximum storage temperature (150C unless otherwise listed).

    In most device, you will hit a limit on output current long before you hit Tj(max).
  • 0 in reply to Emrys Maier
    Intellectual 260 points
    Hello!

    If the junction temperature is not a limiting factor why is there an operating free-air temperature specified from -40 to 85°C ?

    In our application we have the following issue:
    Our whole device is specified for -40 to +85°C. The level shifter itself has the same temperature range.
    The problem is, if the device is getting warmer inside due to self-heating the level shifter is surrounded by a higher ambient temperature (e.g.100°C).

    On the other side we did a worst case calculation of the level shifters power dissipation. After that, we calculated the worst case junction temperature at 85°C => the result is 92°C @ junction.

    This should lead to additional 15°C when ambient temperature increases the ambient temp. to 100°C - therfore 107°C junction temperature.

    Is this assumption correct?
    Does the level shifter have any problems with that?
  • 0 in reply to Markus Nabecker
    TI__Guru* 97046 points
    I see - the system warms up and the SN74ALVC164245 is subjected to operation at 100°C. As you pointed out, the SN74ALVC164245 is only characterized to operate at TA = 85°C -- we do not guarantee it to operate at TA = 100°C.

    I will ask our translation expert to look into options - I'm not sure if we have a 125°C characterized part that is a direct replacement.
  • 0 in reply to Emrys Maier
    TI__Guru 62180 points
    Markus ,

    what is the translation voltage requirements ?
    I can suggest you to use either the -Q1 automotive grade part www.ti.com/.../sn74avcb164245-q1.pdf
    or www.ti.com/.../sn74avc16t245-q1
    or sn74lvc16t245-EP device qualified for military from -55 to 125C.

    will either of these work for your application ?
  • 0 in reply to ShreyasRao
    Intellectual 260 points

    Hello!

    Unfortunately the components you mentioned are not available in 56-pin BGA package. In this application it is not possible to increase the size of the package.

    If I change the part to SN74AVC16T245 a max. junction temperature of 150°C is specified. A maximum ambient temperature of 85°C is also specified .

    If I take the Rth(j-a) of 64.6 K/W i come to the following max. Power Dissipation:

    Pmax = (150 - 85) / 64.6 = 1 Watt

    In our application we have only 150mW. Therefore the ambient temperature can rise up to:

    tmax = 150mW * 64.6 K/W + 85°C =  ~94°C

    Am i right?

    Kind regards,

    Markus Nabecker

  • 0 in reply to Markus Nabecker
    TI__Guru 62180 points
    Markus ,

    The junction temperature beyond which there could be reliability issues is termed as the abs max junction temp for the device which is 150C for most of the logic devices.
    however , maintaining the recommended operating ambient temperature (85C), Vcc, current ensures that the device is complaint to all the electrical specs of the device.