Powering Zumo through VBAT / VB


I’m wondering when not powering the Zumo 32U4 with batteries but an external power supply, would it make more sense to connect it to VBAT or VB? What happens if batteries are present? Does the “reverse protection” avoid that they are charged if VBAT is powered? I don’t fully understand the schematic, but this doesn’t seem to be the case for me.
Besides, would there be drawback of connecting the power supply to VBAT instead of VB? I do not intend to charge the batteries with the external supply, for normal use they would not even be there.

Thanks! :slight_smile:


It is safer to apply external power to VB. If the batteries are installed when you apply power through VB, they will be charged. However, the VB node is before the reverse voltage protection circuit, so you should take care to apply voltage with the right polarity, or you could damage your batteries. If external power is applied at VBAT, it bypasses the reverse voltage protection, which is bad because if the polarity is backwards, it will damage the Zumo 32U4’s electronics. Also, power applied at VBAT bypasses the power switch, so the Zumo 32U4 will always be powered, regardless of the position of the power switch.


I didn’t even think of these simple arguments, but of course they both make totally sense. So I’ll go with VB.

Thank you very much :slight_smile: