synchronous buck converter

[bryce1]

I am trying to develop a circuit to convert 5-18Vdc, 100ma max to 0.4Vdc, 400ma. I am working on a synchronous buck converter design but I am finding limited resources on a discrete design. All of the buck converter IC's I found do not go low enough and have inadequate efficiency when they are even close. I have been toying with the idea of using the basic synchronous converter with a P and N channel fet. The problem is that I am trying to use a MSP430 microcontroller to drive the circuit. What would you reccomend for a gate driver for the upper P-channel fet? If you any other suggestions please put them in too.
Thanks

 

[cbarn24050]

Hi, I'd be inclined to split the converter into 2. Use an off the shelf unit to get down to 3v, then have you discrete converter to go down to 0.4.

 

[felixc]

A synchronous converter can be tricky with a microcontroller, as the timing between the MOSFETs has to be tight to avoid overshoots or a good efficiency.

 

[bryce1]

cbarn24050,
I like that idea, I'll have to look at that one. Efficiency is of great concern so I will have to see if that will work.

felixc,
I haven't seen a problem yet with "shoot through" or efficiency. I have the PWM code already written and put in a delay between switching each seperate gate drive.

The problem I am dealing with the most is that the microcontroller I am using is a 3V logic high and I can't drive the gates with that, especially the P-channel FET.

Thanks for the input so far.