1397 and 1398 mostly look to be pin-compatible, but the documentation I have says they're not entirely so. 1398 operates on a much different V/I which makes it fairly non-suitable for single-chip operations. I've looked into it, and the main regulator engineering would be difficult and probably pretty inefficient. A series string like we did for the R606 would be a lot easier to manage. In any case, a direct chip swap from 1397 won't work.