Buck converter after boost converter -- what is an advantage?

Question

I encountered a mass produced device that has a power circuit like this:

   5V from USB ==[boost converter]==> 13V ==[buck converter]==> 12V

and it confused me. I don't see why you would need a buck converter there.

The 13V rail is connected only to the buck converter, and nothing else. I think you can just set the boost converter to output 12V and omit the buck converter altogether, because power input is from USB and there's no need to drop voltage down (under normal circumstances). Or, if noise is a concern, you might use an LDO in place of the buck converter. However in case of this device the 12V rail is fairly noisy.

What is advantage(s) of this boost+buck configuration, over a single boost converter or a boost+LDO configuration?

EDIT: adding schematic which I reverse-engineered from the PCB, picture follows:

^{simulate this circuit – Schematic created using CircuitLab}

Note: the other side of the PCB is a ground plane. No traces there.

Answer 1

I’d say one possible reason is trust of the boost converter. Anecdotally I know people who see boost converters as a necessary evil, they are unstable and noisy.

These days it isn’t always the case, but you do see output ripple as quite high sometimes on boost converters compared to a similar buck converter. If a 12V rail needs to be very stable, it may be that they are boosting it to over 12V (13V in this case) in a rough and ready manner, and then brining it down to a very stable 12V in order to have the required cleaner supply rails.

We can’t know the real reason without being the designers, but it could be that the cost of getting a stable/clear enough 12V rail from a boost converter alone was higher than using the combination of a boost followed by buck.