I am designing a SEPIC converter using a LT8364 for "power aplications" and a buck converter using a TPS62125 for powering a MCU.
Since I have a bunch (>100pcs) of 100uF, 16V, electrolitic caps laying around, I would like to use them to store a of bit current at the exit of thesse two switching converters.
I understand that using a big capacitor is better if you have an instant and huge current need, but I do not know what happends when you start everything up.
Question 1: Would a 100uF electrolitic capacitor draw an extremly high current at startup, as all capacitors do when they are being charged up and therefore would it destroy the IC or the inductor or would it be just fine because it's only high current for a fraction of a second?
Question 2: Would it be more effective to use a smaller value ceramic capacitor?
P.S. For the SEPIC, output would never go over 14V.
Best Answer
No the IC would protect itself and, in addition, the LT8364 has a programmable soft-start option: -
For the TPS62125, if you read the data sheet it tells you that there is internal current limiting circuit (max 900 mA) - see page 5 of the data sheet - this is to prevent the inductor going into saturation primarily but serves the purpose you appear to want.
There is also a 200 us output voltage ramp time to reach 1.8 volts and this means that dV/dt = 9 V / ms so, if the capacitor is (say) 100 uF, the current cannot be higher than 0.9 amps (coincidentally as per the current limit circuit).
Generally, you can assume most modern switching controllers will have features that protect themselves against load currents that are too high and these are no exception.
Use what is recommended in the data sheets = usually means use a ceramic for modern devices.