Does it need an NMOS at low side with buck?

[mycelldevice]

Hi all:
Does it need an NMOS at low side inside the buck converter?
Because I give a diode at external from gnd to sw.
Thanks very much!

 

[skowe26]

If your doing a synchronous buck converter, then you need it. Otherwise, there is no need to add.

 

[snafflekid]

Need? You don't need a NMOS.

What you should do is calculate the average current flowing through the inductor. Then multiply that by 0.7V and you will see how much power is wasted in the diode. Usually it is important.

 

[vsemi]

Two reasons that you need to use NMOS
1. Customers don't need to use external diode
2. Improve efficiency because Ploss on diode = 0.7V*Iout and Ploss on NMOS= Iout*Iout*Rdson of NMOS