buck converter question: need more current output!

[hazuki]

Hi all! I am trying to build a switching converter that will take 16.5 - 48V and convert it to 15.5V with a maximum current of 16A. Yep, about 250W! I am still a beginner at this, so I am using TI's Webench design tool to help me. The tool doesn't find any solutions for me when I give it my requirements. However it gives me a single solution when I decrease the required output current to 10A. The solution is a synchronous buck using an LM5116 controller.

From some researching (and other forum posts), I have determined that to increase the current output, I need to

A) Use FETs with a higher switch current rating (Is this equivalent to looking for a lower RDSon?)

B) Use a higher switching frequency (downside: decreases efficiency)

C) Use a bigger inductor (Usually marginal gains in current)

I am thinking about taking the design that was generated for me by the tool and simply doubling up the FETs. Is this a good idea? Are there drawbacks besides increased cost?

Furthermore, does the controller care how much current is actually being delivered? Not that I would, but is there anything stopping me from using more and better FETs until I can get like hundreds of amps out of it? I'm assuming the only thing stopping me is gate capacitance?

Thank you!

[Niklas]

Adding more MOSFETs might help a little bit, but not much. The inductor is probably a tougher problem. If you want 15 A output current, then the inductor must handle the peak ripple current of at least 20-25 A without saturating. Also the input voltage can affect the performance as higher voltage typically needs more inductance and lower switching frequency.
Have you thought about a multiphase converter? Split up the current path into several parts, convert and then add together again.

[Richard Head]

I don't mean to discourage you but you really need to understand the intracacies of switchmode power supply design.
The inductor will need to get bigger as well as the power switches and output diode. Also, if you opt for a non-isolated current mode buck converter then you will need slope compensation when the duty cycle gets above 50%, as it will when your input voltage drops below 31V.

[johansen]

the LM5119 is a two phase chip that will do what you want.

it will be a real learning curve to get it working, but the datasheet is well documented.