decap电容的数量根据什么添加啊？

HeshamAhmed

The decap capacitor plays a major rule in the supply behavior in some cases:
- one is when a large current step is withdrawn from the LDO, naturally the LDO will take some time depending on its GBW to respond to this current step so if you have no decap at all the voltage of the LDO will fall down to 0 before the LDO starts working, if you have a decap it will be discharged by I/C for a delta T proportional to the GBW of your LDO so if you don't want your supply to fall down when such a behavior occur you need to determine the size of a decap to give you reasonable drop.
- another is when you have high speed circuits, their activity will cause supply ripples so you need enough decaps to short the supply and gnd of these circuits at the working frequency to keep their vdd-gnd fixed.