I'm working on a portable project that takes 4 (appropriately-rated) Li-Ion cells in a 4S configuration (14.46-16.8V) and boosts it to 27V for a 10-20 Ohm resistive load (soldering iron). The majority of the purpose of the project is because I want the learning experience; I know there are commercial offerings.
Running my numbers, I'll be pumping ~70-80W around, which is higher power than anything I've done before. I spent a good amount of time trying to find a DC/DC converter that could handle the amperage I needed, but ultimately came up short. I DID, however, find an interesting example of a "2-phase converter" in the LT3579-1 documentation (side note: if I drop the out voltage a bit, that converter could handle the load at just about it's absolutely maximum rating... so I have a fallback).
This 2-phase converter had the FB pins and the Error Amplifier Output (VComp) pins of 2 ICs tied together, and the ICs were also synchronized (well, actually un-synchronized, 180 degrees out-of-phase) by way of some included circuitry. That chip is more than I want to spend, but it got me wondering if the approach would work generally for a step-up converter:
- Build N (or maybe N+1 to be safe) identical DC/DC Step-Up circuits on the board
- Tie all the FB lines together, as well as all the VComp lines
- Since the outputs on the DC/DC regulators are already going through a diode, I don't need to worry about the current from one flowing back into another
- Generate a frequency/clock that is (N or N+1) times as high as the IC's spec, then put it through an (N or N+1) divider to clock each IC as out-of-phase with the others as possible.
Is this a reasonable approach? I figure I'll get better efficiency at lower (not TOO low) current, too - so less total heat, plus I'll be dividing the heat that is generated across multiple chips, so it should be easier to manage all around. Am I missing something? Is this a good approach? Are there things I should watch out for - specific regulators that won't work in this configuration, etc? Thank you!