Forced Continuous Conduction Mode (FCCM) in synchronous Buck converter

[balamanikandan]

hi

" Synchronous DC DC Buck regulator with diode replaced or supplemented by a low drop MOSFET across it never enters DCM."

-Refer Switching Power Supplies A-Z
By Sanjaya Maniktala

https://books.google.co.in/books?id...FCCM dcm&pg=PA99#v=onepage&q=FCCM dcm&f=false

Please explain me how FCCM is achieved here?

 

[emontllo]

In a synchronous buck without "diode emulation" high and low side MOSFETS are commutated alternatively (with some dead-time of course).

Since these are bidirectional devices, at low output, after the inductor reaches zero current, it starts to conducting reverse current through the low side MOSFET. Therefore, DCM is avoided. This current comes from the output capacitor, therefore output ripple is increased.

Previous post discussed advantages and disadvantages of this mode of operation:

https://www.edaboard.com/threads/248280/