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Question with Thermal Shutdown and Junction Temperature

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FreshmanNewbie

Advanced Member level 1
I'm using this Battery Charger IC - MCP73831.

So, I am using a SOT-23 package.

My input is 5V, the output Vbat charge regulated voltage on the Vbat pin is 4.2V and the maximum charge current is 340mA.

So, by calculation of power dissipation as per section 6.1.1.3 on page 18, it says that, for my condition,

Power Dissipation = (5V - 2.7V) * 0.34A = 782mW

Maximum junction temperature = (0.782 * 230degC/W) + 25deC (ambient) = 204degC approx.

But on page 3, absolute maximum ratings for maximum junction temperature are given as "Internally limited".

My questions:

1. What does "Internally limited" mean for junction temperature?
2. While searching for this answer, I searched for thermal shutdown and found section 4.10 on page 14 which says that the device will go to thermal shutdown if the die temperature exceeds 150degC.
So, according to my calculation, the junction temperature (204degC approx) exceeds the 150degC. So, for my application, when the die temperature or that is, the junction temperature comes close to 150degC and exceeds it, the device will go into thermal shutdown and my device would start to cool. Only if the temperature goes 10degC than 150degC (as mentioned in section 4.10), the device will start to work again and goes in a loop is it?

So, the device will always be stuck in this cycle and will never fail due to excessive junction temperature which is why they mentioned that the junction temperature will be internally limited, is it?

Hi,

I did a PDF search on "limit" and found..
"4.9 Thermal regulation"

Klaus

Shutdown response may be "real time" (probably with some hysteresis)
or latched. The latter is popular in consumer equipment because it
makes the consumer responsible for re-starting after any thermal
fault shutdown (no "motorboating" along the underside of thermal
shutdown threshold). But my customers often prefer a "self-righting"
fault response as there's one mission, and best finish it.

What do you think about my situation and other questions?

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