Buck Converter - Inductor CCM and DCM

Question

I have a doubt while selecting the inductor for a buck converter.

TI App Note

In This app note, in the abstract itself, they mention that this :

This application report gives the formulas to calculate the power stage of a buck converter built with an integrated circuit having a integrated switch and operating in continuous conduction mode.

This not mention anything about the DCM mode. So, does it mean that, if I follow the mentioned steps in the app note, for my Vin, Vout and Iout, I will not enter the DCM mode?

I understand about the DCM mode. But in this case, what care should I take while designing such that my selected inductor does not enter DCM.

Vin = 3.3V

Vout = 1.8V

Iout = 0.4A

Selected Inductor = 22uH

Answer 1

what care should I take while designing such that my selected inductor does not enter DCM.

If the chip itself can handle the transition from CCM to DCM then that should be OK. Changing from one mode to the other necessitates a change in how the control loop works and, if the chip is capable of handling this change automatically (many are of course) then there's usually no need to worry.

On the other hand, if you designed the inductor for DCM mode and it entered CCM mode you might get problems but, this is not usually due to the chip. DCM requires an inductor of lower value and, as such never sees the same peak current as might happen in CCM mode so, under these circumstances, the inductor might saturate.

Going from CCM to DCM usually isn't a problem and quite often happens when the load is very light because DCM can handle much lower energy transfers per switching cycle.