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TPS7B82-Q1: Vout Short to GND cause a damage to IC?

Part Number: TPS7B82-Q1

Hi team,

In the case that the output is shorted to GND, the device continues the current limit and the thermal shutdown cycle repeatedly.

If this condition continues, does it cause a damage to the device?

It looks the TSD(max) is higher than the absolute maximum temperature. So, in the above case, the Tj may exceeds Tj-abs max repeatedly. I concerned about if it damages to the device.

Regards,

Saito     

  • Hi Saito, 

    If the device is operating in current limit/thermal shutdown for an extended period of time, it will get damaged. 

    Best,

    Juliette

  • Hi Juliette-san,

    I believed the thermal shutdown is implemented to prevent the device damage from such a conditon like Vout to GND short. 

    Could you clarify how much period of time can the device tolerate the Vout to GND short condition, second order or minute order?

    Regards,

    Saito

  • Hi Saito, 

    It seems I misspoke. The device can go in and out of those protection modes, you are correct. The longevity of the part will go down. Having any electrical component running for a long time at high temperatures will degrade the part over time. 

    Sorry for the confusion, on my end. 

    Best,

    Juliette

  • Hi Juliette-san,

    Thanks.

    >The longevity of the part will go down. Having any electrical component running for a long time at high temperatures will degrade the part over time. 

    That make sense.

    >It looks the TSD(max) is higher than the absolute maximum temperature. So, in the above case, the Tj may exceeds Tj-abs max repeatedly. I concerned about if it damages to the device.

    What does your team think of this? The device may exceed Tj abs max because the TSD temperature is higher than Tj abs max. Is there no concern the device will get damaged? Just the longevity will go down?

    Regards,

    Saito

  • Hi Takahiro-san,

    The max operating condition of 150C is meant to indicate the maximum temperature the device can operate at before thermal protection kicks in.  The device is effectively "non-operational" while thermal protection circuitry is turning it off.  Common assumptions in device reliability reports are a junction temperature of around 55C.  So when the device is exposed to elevated temperatures, especially above 150C, it will be expected to have a reduce operating life.

    Otherwise, you need a stimulus which is so extreme that it exceeds the bandwidth of the device to react, while simultaneously breaking something in the device.  Over current protection has a finite bandwidth, so a severe short to ground which exceeds the current rating of the bond wires and causes them to fuse would be an example.  Keep in mind that I have no examples of this ever happening on any device, so I don't think it's very likely.  Another example would be a sudden temperature rise in the junction before the LDO can turn the circuitry off.  This is also highly unlikely as the bandwidth of a thermal limit loop would be expected to be orders of magnitude faster than the thermal time constant of the device.

    Another thing to consider is that we routinely test our devices operating in and out of thermal limit, inside ovens, for various tests for customers.  At the end of the test we consider the device "consumed" as the life has been reduced from the part.  I think your biggest concern will be reduced operating life in this case.

    Thanks,

    - Stephen

  • To add to Stephen's reply:

    Section 7.3 on Derating in the Linear Regulator Design Guide shows the Arrhenius Model used to predict semi conductor reliability. 

    The JEDEC standard we test our parts under guarantee a 9 year lifespan if operated at 55C. For power parts, however, 55C is not typically the temperature the junction runs at. The lifespan of the part degrades exponentially with temperature. 

    Best,

    Juliette

  • Hi Stephen-san,

    I appreciate the detailed explanation. I understand the lifespan will degrade severely especially when the Tj stays above 150C long time. Also, the hard short to the GND has a risk of the over current that have a possibility to get damaged to the device.

    Regards,

    Saito

        

  • Hi Juliette-san,

    Thank you for your answer from the point of view of JEDEC standard. I understand the temperature rise causes the lifetime degradation.

    Regards,

    Saito