Has Enpirion planned a silicon revision of EM21xx to allow a straight synchronization by driving a simple external SYNC clock signal, as already do very well the others Enpirion EN63A0QI, EN6347QI, (Intersil and LT synchronous DC-DC buck devices too) present on my board?
I can't think that this "main device" cannot synchronize and place with a know skew with the others DC-DC, when today it's typical to have a lot of them on the same board.
that's no synchronization by external SYNC signal.
By PMBUS command (MFR_RESYNC command) you can just "open a time window" for a temporary re-alignment with a single edge of external SYNC signal but the EM21xx will never stay locked cycle-by-cycle in frequency and phase with the external SYNC signal, like all other DC-DC.
Just a bit after a MFR_RESYNC command, the EM21xx will start to shift frequency (and phase, of course) to the its free running frequency.
The behavior is substantially different compared to the other synchronous DC-DC, EN63A0Qi and EN6347QI included. Isn't it?
You are correct and SYNC function for EM21xx is different than what in the analog parts and below how it is working: