Hi,
We use the LT3645 to generate 5V & 3.3V from a 24V DC source as per the following circuit. The 5V output from the buck regulator is used as the input to the linear regulator.
With a recent build of units fitted with the LT3645HMSE regulator model, we have noticed that some units operate with a slighter higher input current (~3mA @ 24V) than other units.
Upon further investigation, we have found that (by observing the SW node voltage on a scope):
- The regulators with the higher input current operate in a discontinuous switching mode.
- The SW node voltage is not clean and contains some ringing.
Please see the attached document for some scope traces and more detail of the problem.
We would like to know:
- Why do some units operate in a discontinuous switching mode while others operate in a continuous switching mode?
- What would be the recommend inductor value for our application?
- Would there be any long term reliability issues if we continue to use the circuit as is?
- Do you have any other suggestions or circuit changes we could make to improve performance?
Thanks,
Kieran
