I'm working on a design where the LM43600 step-down is on the secondary side of a flyback.
To reduce ripple currents and noise in general (the board includes some precision ADCs etc.), it would be nice if the step-down draws current at the same time as the flyback rectifier diode conducts. But I don't see any spec of the relative phase between sync input and power switch.
I think there may be a PLL inside, as it is capable to sync to higher or lower frequency than free-running one.
But it depends on the internal phase detector (in a 4046 PLL you have 3 different ones, for example).
The primary of the flyback is LM5015 (powered from 802.3af PoE), I can sync it from the LM43600 as well, but it has the unpredictable internal divide-by-2. So it's easier to sync the flyback with 500 kHz pulses by small transformer (cost or size is not an issue in this project, it's not a mass-produced $9.99 consumer product but some special equipment in 19-inch rack size) from secondary to pirmary, and then sync the LM43600 with 250 kHz pulses from the flyback seconday winding. But I don't know the phase relationship. Ideally, the LM43600 step-down turn-on should be close in time to LM5015 flyback turn-off (secondary diode turn-on). It doesn't have to be exact, but it shouldn't be 180deg out of phase as that would maximize ripple.
Any suggestions?