Comment by labcomputer
Comment by labcomputer 11 hours ago
The app notes and data sheets of related parts suggest that the target application is large conversion ratios, where the duty cycle in an inductive converter is close to 0 (or 1). That forces tradeoffs, like a lower switching frequency (lower efficiency), a larger inductor (more weight and/or cost) or very short T_on for one of the FETs (lower efficiency because transition times become important). So you can use the charge pump as the first stage of a hybrid converter to get a higher system efficiency.
My recommendation to anyone who finds themself stuck in this corner of the design space is to consider a tapped inductor converter.
I did a tapped inductor boost last year to take 3V input to 80V output (at not-much output current, I forget exactly what it was but it was mostly a bias voltage; also, the actual output voltage was DAC-set and could be quite low, so the loop dynamics were unpleasant). It was definitely annoying to wrap my head around, and very annoying to select the inductor (Würth has a nice OTS series, at the usual Würth prices; HVM would likely want a custom or semicustom design) but it just plain worked the first try and continued working through the usual stress tests and also the unusual stress tests of the Very Expensive Load™ getting itself Very Expensively Killed™ (for non-power-supply reasons). I was really happy with that converter, that kind of step-up ratio isn't easy and it just worked.