What I mean by that is to adjust the voltage output of the converter to match the voltage of the GoPiGo3 board. this allows them to contribute power equally.
What I did was slightly different:
I measured the 5v with an Official Raspberry Pi-4 external supply attached, and then without.
With the external supply attached, the 5v measured almost 5.2v and without about 5.0 - so I adjusted the buck supply to provide the 5.2v the “official” supply provided.
This “over drives” the GoPiGo’s supply so the external supply provides the lion’s share of the 5v power, allowing the GoPiGo’s board to provide an increased amount of 12v power to the circuitry that needs it.
Should the external buck converter droop for whatever reason, the GoPiGo will pick up the slack.
The one thing I don’t like is that neither of the supply outputs are diode isolated so, theoretically, one supply can back feed power to the other which is not good.
However, since it is not possible to exactly balance the load-sharing between the two supplies without significant modifications to both supplies, I decided to imitate the action of the external Raspberry Pi supply.
What I am hoping happens is that with the output of the buck converter set higher than the GoPiGo’s 5v buck converter, the GoPiGo’s converter will detect a higher than needed voltage and shut down because it doesn’t need to supply additional power.
The result should be that the VCC voltage rises slightly because it is not providing power to the 5v circuitry anymore, (or is providing only de minimus power to keep the circuit alive) - which is exactly what appears to happen because the VCC voltage does rise slightly when I overdrive the 5v rail.
This should allow the excess battery power to provide extra power to the GoPiGo circuits that need it.