If I drive the SYNC pin from a 74LVC inverter (3.3V CMOS output):
1. should it be AC coupled?
2. If AC-coupled should I pull-up/pull-down the SYNC pin at the LTM8074 side to define operation at startup?
1) This pin does not need to be AC coupled.
2) The setup on the SYNC pin depeneds on what mode of operation the LTM8074 should be in. Page 10 of the datasheet will provide description for the SYNC pin. Below is the snippet on the different modes and how to change the SYNC pin to match that mode:
- Burst Mode® Operation. Tie this pin to ground for Burst Mode operation at low output loads—this will result in ultralow quiescent current.
- Pulse-skipping mode. Float this pin for pulse-skipping mode. This mode offers full frequency operation down to low output loads before pulse skipping occurs.
- Spread spectrum mode. Tie this pin high (between 2.9V and 4.2V) for pulse-skipping mode with spread spectrum modulation.
- Synchronization mode. Drive this pin with a clock source to synchronize to an external frequency. During synchronization the part will operate in pulse-skipping mode.