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TPS92629-Q1: In what cases does a thermal shutdown trigger?

Masaru Oinaga
Expert 4425 points
Part Number: TPS92629-Q1

Tool/software:

Hello, Experts,

Our customer is testing the protection feature of TPS92629QDGNRQ1 and would like to know how they can trigger thermal protection. The IC has a short-to-GND protection and the output current is limited when output is shorted to ground, so the IC itself does not heat up enough to trigger thermal shutdown.

We think that this "thermal shutdown" is expected to be triggered mostly when heated by surrounding environment i.e. ambient temperture rise due to LEDs; is this correct understanding? What else is the expected case which triggers a thermal shutdown?

Best,
Masaru

  • +1
    TI__Genius 11765 points

    Hi Masaru-san,

    I would not expect a short-to-ground fault to trigger thermal shutdown because the TPS92629-Q1 limits the output current to 5mA during the fault condition.

    Assuming a battery voltage of 12V, the internal power dissipation in this case is 12V × 0.005A = 60mW. A rough estimate using only the θJA parameter indicates that the junction temperature will rise by approximately 60mW × 50.7°C/W = 3°C. Assuming the ambient temperature is 25°C, the junction temperature is therefore 28°C whereas the typical thermal shutdown threshold is 172°C.

    You are correct that you should consider the ambient temperature, however you must also consider the internal power dissipation.

    Consider a case in which the battery voltage is 12V and the output current is 250mA across a single LED with a forward voltage of 3V (assume no thermal sharing resistor is used). The internal power dissipation is (12V-3V) × 0.250A = 2.25W. A rough estimate using only the θJA parameter indicates that the junction temperature will rise by approximately 2.25W × 50.7°C/W = 114°C. If the ambient temperature is 65°C, the junction temperature is 179°C and the device is likely to enter thermal shutdown.

    Regards,

    Zach

  • 0 in reply to Zach Olson
    TI__Expert 4425 points

    Hi Zach,

    Thank you for your explanation. It is very helpful.

    Best Regards,
    Masaru