Power WB55 via 5V Pin and have USB connected at the same time

[XG]

Hi,

is it safe to interface a WB55 via USB and simultaneously power it via the 5V pin from some external batteries? The battery-voltage I use is limited to 5V. I have some concerns about bricking some electronics due to multiple grounding. Are there some safety measures in place against it?

[TDK]

With multiple power supplies you need to ensure supplies do not power each other. That can be done by using a schottky diode between the supply and the VCC rail, or some other such isolation.

There are no issues with multiple grounds.

[XG]

What I forgot to mention:grinning_face_with_sweat: I'm using the WB55 on a nucleo board. See the schematic here. It has some diodes on it protecting the 5V pin. Do you think this is sufficient? I'm more of a programmer I can barely read these schematics. I'm surprised I even understand that there are diodes on it. But no schottky diodes I think :thinking_face:.

[AScha.3]

>is it safe to interface a WB55 via USB and simultaneously power it via the 5V pin

Which USB ? from st-link usb there is a power switch, to enable/disable connection.

And JP3 is there, to let you connect the source, you want.

"USB and simultaneously power it via the 5V pin " is no good idea , set the jumper on JP3 to the source you use, thats simple and safe.

Why you want "USB and simultaneously power it via the 5V pin " ?

[TDK]

If JP1 is configured so that USB can power the board, USB VBUS and 5V are directly connected without protection diodes in either direction. It is not safe in general to power both at the same time.

If VBUS is higher than the batteries, this will cause current to flow into the batteries--not safe.

If VBUS is lower than the batteries, this will cause the batteries to back-power VBUS--not safe.

If you mean the ST-Link USB connector, current from the batteries is blocked from powering VBUS, but not the other way around--not safe.

[XG]

I don't necessarily want to power my Nucleo WB55 via USB. I just want to read out any serial data that's transmitted over it. The peripherals i use (a SIM modem in particular) require short current peaks that the USB port of my PC isn't able to provide. Therefore I added some batteries and capacitors. I think you mixed up Jumper 1 and 3 a little. According to this document (Section 7.13) JMP1 has multiple connectors. Although I'm not sure if that document is describing that exact chip.

Curently I only have connected JP1 (1-2) on my board. If they are connected does that mean they are open or closed? I assume closed? So is there no way how I can interface (no powering) via USB and power via an external power supply?