Odd problem: Very high step down ratio switching converter

[Speakerguy]

I've got a problem. I need to convert nominal 28V (which is allowed to be up to 32V in the system I'm in, but we need/want to protect up to 36V on the input to our regulator for spikes and such). We need to buck this down (or use some other type of step down switcher) to get this to very low levels - 3.3V, 1.6V, etc.

Is there a particular converter or topology I should be looking at? Most simple buck converters look like they are going to be only about 65% efficient in these scenarios, and heat is being an issue in our current design. Thanks!

 

[crutschow]

The usual question. What's the current required?

 

[Speakerguy]

Several amps output. Right now we are using four buck converters for different voltages on the board (3.4V, 1.6V, etc) and then using LDO's after them to kill ripple and step down a touch more. Each of the four buck converters is rated at 2A max. I'd say we're probably drawing 50-80% of what the regulators can do, depending on section.

But 2 amps min if we stay with multiple bucks, let's say 6 amps out max if we use one big buck to get from 28 to a more reasonable voltage (3.3V). I'm thinking a forward converter or something similar will end up being the most efficient.