I have a doubt with inrush current limiting for an LDO. To understand that, I referred old literature of capacitors and others. I have some conflicting arguments which I need to clear out:
This is from Wikipedia:
The current into a capacitor is known to be
: the peak inrush current will depend upon the capacitance C and the
rate of change of the voltage (dV/dT). The inrush current will
increase as the capacitance value increases, and the inrush current
will increase as the voltage of the power source increases. This
second parameter is of primary concern in high voltage power
distribution systems. By their nature, high voltage power sources
will deliver high voltage into the distribution system. Capacitive
loads will then be subject to high inrush currents upon power-up.
The stress to the components must be understood and minimized.
This passage says that inrush current depends upon capacitance
value, voltage to applied to it.
- From my basic understanding: for sudden changes the capacitor is a short and the capacitor will not allow any changes in voltage suddenly. So, when we turn ON power at that instant C will be short having 0 voltage across it. So the max current will depends on the ESR of cap and any series path resistance. It doesn't depends on the capacitance value.
This passage says: Inrush current depends on ESR of the cap and not on value of capacitor, which contradicts the previous passage.
From all these how can we calculate how much transient will there be?
One more confusion: most of the regulators specify controlled slew rate of the output to mitigate this inrush current limiting problems. But the slew rate limiting will work for capacitors connected on the output side. But there will be capacitors that will be connected on input side of the regulator. Will those have large currents?