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:
- When the SYNC pin is configured as input clock, the external clock need to be available before the EM21XX is enabled.
- EM21XX will only lock to the external clock within 1ms after the device is enabled.
- After the device already locked to the external clock, It will not respond to any change on the external clock, so if that signal disconnected the EM21XX will continue working with the old clock value and will not be affected.
- EM21XX can be re-synchronized to the external clock signal next time when the external clock has been updated via PMBus MFR_RESYNC command.
- Sync function will not generate any spike on the output under any condition.