Some Practical PD Design Issues
We must keep in mind that once the PSE applies power to the port, it starts an internal inrush timer too and will shut down the port if things have not stabilized at the end of that period. Think of this as a race situation, and the start of that inrush interval as a starting gun. We must complete the race in the ascribed time, or be disqualified. For example, if we put a very low current limit on the PD’s pass-FET and/or an excessively large bulk capacitance, we will not have stable conditions when the inrush timer times out. So the port will be shut down. This also places limits on the amount of bulk capacitance. For example, if the PD places a current limit of 100 mA, then, to complete the charging within 50 ...
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