When you have a load that could feasibly be run across a wide range of currents, should you design a SMPS for the max load even if that means the typical usage falls into the discontinuous operation region. Or can you design for typical usage and just ensure the inductor is rated to handle the max usage too?
For example, I'm selecting an inductor for a 12V to 5V step down buck using the LM2596. The max load would be slightly below 2.5A if I maxed out the device processing + maxed out its USB current supply.
Doing the calculations for 2.5A max, 12 in, 5V out, I have an E.T of 18.88 which if I use with figure 30 of the datasheet (see attachment) @2.5A puts me slap in the middle of the L41 region a 33uH inductor.
So far, so good. Using figure 31 gives peak-to-peak ripple current of ~600mA and a peak switch current of 2.8A. Which when plugged into the min load before discontinuous operation gives 600mA/2 = 300mA.
Now what if I expect the device to operate generally at 250mA even though in some circumstances it could be used at 1A or up to 2.5A at the extreme. That would cause it to generally be running in the discontinuous region. That would seem like a poor selection of inductor?
In this case would it be safe to instead design the supply using an inductor choice based around a typical usage current rather than max load, resulting in a higher inductor selection due to lower load and a lower discontinuous cut off point (for example 200mA) but still ensuring the inductor was safe to use all the way up to 3A?
Datasheet LM2596]