I'd like to know whether there are any sequencing requirements for supplying an external clock to the LTM4644 CLKIN input.
The datasheet only states the frequency range (1MHz +- 30%), minimum voltage level (>2V), and that the PLL is disabled during start-up, but leaves some points open:
- What clock is used during start-up? Is it the internal 1MHz?
- Can a clock be supplied without VIN being present? The Absolute Maximum Ratings suggest no, since no INTVcc is not present in that case.
- If applying the Clock after VIN, are there any time constraints?
The following questions are to plan for failure modes:
- What happens if the clock to CLKIN is stopped while outputs are enabled (either at low, high or high-Z state)? Will the internal 1MHz take over or will this result in outputs becoming unregulated? If the 1MHz take over, how fast does this happen?
- What happens if the clock to CLKIN (within the specified frequency range) is applied when the LTM4644 is already running from the internal clock and has outputs enabled? Will this lead to (transient) changes in output voltages and/or outputs becoming unregulated?
Thanks for your assistance