Is it a problem if an inrush current that exceeds the absolute maximum rating flows at startup?
LDO Linear RegulatorsProtection
In most cases, there is no problem.
The inrush current that flows when an LDO starts up is mainly a current to charge the output capacitor.
There are two points to consider about this inrush current: current value and heat generation.
For many LDOs, the inrush current at startup exceeds the absolute maximum rating, but the overcurrent protection function suppresses excess over current.
Also, when considering the duty of inrush current in the product life, the accumulated time is very short.
So, if steady state is designed within the absolute maximum rating, inrush current is usually not considered as a problem.
Regarding heat generation, calculate the junction temperature (Tj) using the transient thermal resistance, and there is no problem as long as it does not exceed the absolute maximum rating (Tjmax).
The transient thermal resistance value (Δθja) increases over time and eventually becomes equal to the thermal resistance value (θja).
For many packages, the transient thermal resistance value (Δθja) of 1 ms is about one order of magnitude smaller than the thermal resistance value (θja).
The period which an inrush current flows when an LDO starts up is often 1 ms or less.
Then, In case the steady state system is designed properly using thermal resistance value (θja), heat generation by inrush current will not be a problem.
For example, if a large-capacity output capacitor is connected such that it takes more than 100 ms for start-up, detailed consideration is required.
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