I'm designing a device with several ICs and they require so many different input supply voltages. 18V, 12V, 3.3V, 1.8V 1.3V.
18V will probably use around 80W out of 100W(20V, 5A) main supply budget and 3.3V~1.3V will probably use around 1A~2A.
So, I was thinking of using a couple of LDOs in parallel to relieve thermal issues for the 18V source and use a buck converter to make 20V into 5V and use LDO to supply 3.3V, 1.8V, and 1.3V.
But I'm not so sure if it's ok to directly connect buck converter and the LDO to a single 20V,5A power supply rail. My concern is that during operation, LDO and buck Vout could be unstable when either one pulls currents hard.
I'm thinking Al caps with high capacitance could help, but is this enough to maintain stability? Are there good guidelines for using linear regulators and switching converters?