Selecting capacitor and inductor for adjustable buck converter

Question

I'm trying to understand how to choose the right inductor for a buck converter that can produce different output voltages.

When using an LM2596 I can add a potentiometer into feedback loop to produce an output voltage between 1.8 V and 12 V, but the data sheet gives different recommended values for inductor and capacitor depending on the output voltage: between 15 μH and 22 μH and capacitors between 330 μF and 820 μF.

Is it possible to select inductor/capacitors to fit an output voltage range (like pick the max values), or do I need different circuits for different voltage ranges (like for 1-3 V, 3-6 V, 6-9 V, etc.)? What are the drawbacks of an approach using a larger than required inductor or a larger than required capacitor?

Answer 1

It is possible, but then you might compromise size, power limit, regulation, current*DCR or cost for an oversized inductor or perhaps adding heat vs removing PCB heat or affecting the step current overshoot from min load to max load without considering all the variables that affect damping.

Consider the energy stored in the inductor also and the energy tranferred to the load with some ratio for damping might require a larger peak/average current and thus increase cost.

Variable load current with bi-directional steps is the hardest test of stability (overshoot) for an underdamped RLC switched filter and choice of LC is critical along with ESR, DCR and error voltage.

Answer 2

I have never used LM2596 but I have built circuits with LM2596HV that happily output an adjustable 1.23-55 V supply apparently 1.23-63 V although I have not tested them above 55 V. do you specifically have to use LM2596 or would this schematic and board layout help you any (ignore R4, it was a fixed resistor replacement for the POT).