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LM25037-Q1: Thermal Protection

Shrikrishna Kaje
Prodigy 20 points
Part Number: LM25037-Q1
Other Parts Discussed in Thread: LM25037

Hello,

My Query is regarding Thermal protection given in section 7.4.6 of the datasheet LM25037/-Q1 Dual-Mode PWM Controller With Alternating Outputs.

The above mentioned section says “Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event the maximum rated junction temperature is exceeded.”

- Does the term junction temperature here pertain to the junction temperatures of Power MOSFETS used in Drivers of pin OUTA and OUTB ( Here I'am assuming that Power MOSFETS might be used in Main Output drivers of LM25037 )  ?  If it is not then, Can I get some more detailed information regarding junction tempertature of LM25037 IC.

Best Regards,

Shrikrishna 

 

  • 0
    TI__Genius 13660 points
    Hi Shrikrishna ,

    The junction temperature (TJ) mentioned in 7.4.6 means the junction temperature of IC LM25037. It doesn't mean the external power MOSFETS's.

    Maximum junction temperature (sometimes abbreviated TJMax) is the highest operating temperature of the actual semiconductor in an electronic device. It is used when calculating the necessary case-to-ambient thermal resistance for a given power dissipation. This in turn is used to select an appropriate heat sink if necessary.

    If the temperature rises above the TJMax, this will trigger a protection mechanism to cool the processor to prevent damage. For LM25037, When activated, typically at 165°C, the controller is forced into a low power standby state with the output drivers (OUTA and OUTB) and the bias regulators (VCC and REF) disabled. This helps to prevent catastrophic failures from accidental device overheating. During thermal shutdown, the soft-start
    capacitor is fully discharged and the controller follows a normal start-up sequence after the junction temperature falls to the operating level (140°C).

    An estimation of the chip-junction temperature, TJ, can be obtained from the following equation:
    TJ = TA + ( RθJA × PD )...
    where: TA = ambient temperature for the package ( °C )
    RθJA = junction to ambient thermal resistance ( °C / W )
    PD = power dissipation in package (W)

    Regards,
    Teng
  • 0 in reply to Teng Feng
    Prodigy 20 points
    Hello Teng,

    Thank you for the response.

    In your answer, you have mentioned
    " An estimation of the chip-junction temperature, TJ, can be obtained from the following equation:
    TJ = TA + ( RθJA × PD )...
    PD = power dissipation in package (W) "

    - How is power dissipation ( PD) in package for LM25037 is calculated as there no sufficient information about
    Internal MOSFETs/Switches given in datasheet ?

    Regards,
    Shrikrishna
  • 0 in reply to Shrikrishna Kaje
    TI__Genius 13660 points
    Hi Shrikrishna,

    From the datasheet, the typical supply current into VCC from external source is 4mA when VCC is 10V, so the typical PD is 40mA. For the actual operating supply current, you can measure it by the multimeter or other current measuring instruments.

    Regards,
    Teng