Connection between BAT- and GND pins on A-Star 32U4 Mini ULV


Why is there a specific BAT- pin on this board? How is it interconnected to the GND pins ?

Thank you in advance.

The schematic for the 32U4 Mini ULV is here: … ematic.pdf

As you can see, on this particular model BAT- is not directly connected to ground, but is part of the power supply transition feature.

Thanks for the link.

Is the role of Q2 to prevent damage in case of of a polarity inversion when connecting a battery?


Yes, Q2 is part of reverse polarity protection circuit. Please note, the ULV version of the A-Star Mini uses a different reverse polarity protection circuit than what is found on the LV and SV versions. On the ULV version, a N-channel MOSFET is connected to BAT-, and on the LV and SV versions of the A-Star Mini, a P-channel MOSFET is connected to BAT+.

- Jeremy