I'm unclear about how the external synchronization mode works. This is the description in the datasheet:
"
In external synchronization mode, a resistor is connected between the RT pin and GND. The Sync pin requires a
toggling signal for this mode to be effective. The switching frequency of the device goes 1:1 with that of Sync pin.
External system clock-user supplied sync clock signal determines the switching frequency. If no external clock
signal is detected for 20 μs, then TPS50601-SP transitions to its internal clock, which is typically 500 kHz.
"
I bolded the text at issue. Does this imply that I need to start the external clock within 20 us? Or is it possible to let the regulator start in the default (500 kHz), then begin external synchronization seconds or minutes later? I feel like being able to start synchronizing later is typical for switching regulators, but the datasheet seems to imply that it might not be ok?
Thanks!