Hi Anston, thanks for the suggestion. The LM22671 does look interesting. By the way, it does not show up at all in the Webench selection tool. And if I try to find it with the parametric selector tool, it is listed in the overall list, but drops out when I select "frequency synchronization" as a required feature. I suspect that a lot of people may be missing what seems to be a very good part, one that apparently has been available for five years or so.
Also, in general, if one selects "inverting buck-boost" as the topology in the parametric selector, most of your buck converters are filtered out. This seems unfortunate, since pretty much any buck converter can be used in the inverting configuration.
One concern that I have with the LM22671 is the use of the sync pin. For my application the sync signal will not be available until sometime after power up. At first I read the datasheet as implying that the signal has to be present from the beginning, since the mode of the pin is set 100us after power up. But reading between the lines, there is the *suggestion* that even when the mode is latched as ext. sync, if the external signal is not present the chip will continue to run on its internal ~500 kHz clock. Is that the case? Can the external signal be applied and removed arbitrarily, with the chip then switching between the external signal and the internal clock as needed? If so, what does that transition look like? Will it be smooth, e.g. as if mediated by a PLL? Or wil there be a discontinuity that may cause a glitch in the output voltage?