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TPS7B81-Q1: when does the thermal shutdown feature will enabled

Karthik Anandan
Prodigy 10 points
Part Number: TPS7B81-Q1

Tool/software:

Hello Together,
I am using the TPS7B8150QDGNRQ1 (Fixed 5V version) in one of our applications. As per the datasheet, the thermal shutdown is specified to occur at 175°C (device turns OFF) and the device resumes operation when the temperature drops to around 155°C.

However, I noticed that the maximum allowable junction temperature is specified as 150°C, which appears to be contradictory.. Can you elaborate on this?

Additionally, I would like to understand the behavior of the LDO when the output (5V) is shorted to ground. In our case, the input voltage is 18V.

  • 0
    TI__Genius 13670 points

    Hi Karthik,

    Please note that the recommended operating max temp is 150C for the junction. The abs max ratings are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. That said, I will check internally and update here if the 150C abs max is a typographical error in the datasheet.

    Karthik Anandan said:
    Additionally, I would like to understand the behavior of the LDO when the output (5V) is shorted to ground. In our case, the input voltage is 18V.

    When output is shorted to GND, the current limit/ short circuit fault protection limits the current through the pass element to I(LIM) to protect the device from excessive power dissipation. Fig 5-14 shows the I(LIM) value with respect to temperature (ambient). If at any point, the VIN-VOUT difference causes the power dissipation Pd = (VIN - VOUT) x I(LIM) to increase the junction temperature above 175C, thermal shutdown shuts off the output. The output recovers after the junction temperature reduces by 20C. The device can cycle between current limit and thermal shutdown until the short to GND on the output is removed.

    Regards

    Ishaan

  • 0 in reply to Ishaan Shetye
    Prodigy 10 points

    Hi Ishan,

    Thank you for the information.

    Could you please confirm the absolute maximum rating for the junction temperature?

    Also, as per my understanding, in the event of a short to ground at the output pin, the current is limited between 180mA and 690mA. Typically, this causes a rise in the LDO temperature. If the temperature reaches 175°C, thermal shutdown is triggered. In such a scenario, could you please confirm whether the IC experiences any degradation in functionality?

    Looking forward to your confirmation.

  • 0 in reply to Karthik Anandan
    TI__Genius 13670 points

    Hi Karthik,

    I will confirm with our design team on the absolute maximum rating for the junction temperature and get back to you. 

    Karthik Anandan said:
    In such a scenario, could you please confirm whether the IC experiences any degradation in functionality?

    For continuous normal operation, the junction temperature must not exceed the TSD trip point. If the junction temperature exceeds the TSD trip point, the output turns off. When the junction temperature falls below the TSD trip point minus the thermal shutdown hysteresis, the output turns on again. The device can keep cycling between an ON state and OFF state due to thermal shutdown but this is expected behavior. No degradation in functionality is expeccted in this case