Connecting the grounds on a non-isolated DC/DC converter

Question

For isolated DC/DC converters, I know that it's a good idea to have two different grounds on both sides and that we should avoid to connect the two grounds together as the isolation is useless when they are connected. But what about non-isolated DC/DC converters ?

I want to know if it's a good idea to connect both sides of the converter to GND (circuit A), or if I should only connect one side to GND and connect the other side like if -VOUT was a GND (circuit B)

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

Your illustration show that -VIN and -VOUT are the same grounds. So it's theoretically the same potential to both side. I.e. it's a wire. You can ground both side to improve output decoupling and stability. This create a second way for the current to flow to the ground. However, be careful with some non-isolated dc/dc converter module witch integer a current sensing on the ground return. In this case, a small voltage drop appear between -VOUT and -VIN so you should not to ground the output in which case the module will not work (or at least, current limitation will not work).