Cant power B-L072Z-LRWAN1 with battery

[KPage]

We recently received our B-L072Z-LRWAN1 but are not able to run the program while batteries are plugged in. In the datasheet it says that we need to remove SB37 to accomplish this. But then I cant program it anymore? How can I use the board with battery only and still be able to program it?

[Tesla DeLorean]

Check the version of ST-LINK firmware being used. V25 might have an issue holding in reset.

@Andrew Neil​ identified and issue with a resistor or diode causing higher current draw​.

[Andrew Neil]

Are you able to "run the program" when powered from any of the other power sources?

Have you studied the schematics? They show why powering the device from the battery doesn't power the ST-Link.

As the UM tells you, the reason for removing the link is because the ST-Link doesn't get powered from the battery.

But, when you are programming, the ST-Link requires a USB connection anyhow - so it will be powered from that!

So you should be able to fit the link for programming while the ST-Link has USB power, and then remove the link to run on batteries ... ?

[JustMe]

I am having a similar problem. It works fine when powered from usb but when I try with batteries the LED lights up but it does not seem to transmit anymore. I have checked the schematic and the LED comes from the '5V ' line. This receives power from the various sources through diodes. I have tried with and without SB37 and still not transmission.

I have done some more testing and found that it only works when the stlink usb is used for power. None of the other power sources seem to work. Even though they do power the pcb as far as I can tell

[T J]

its just 2 batteries ? 3V not 5V...

I cant test it easily.

[JustMe]

With the linkUSB plugged in the MCU_nRST pin is at 3.3v. With any of the other supplies connected the MCU_nRST is at +- 1.5v. I have searched the schematic and can see no reason why this could happen. I am beggining to think that the schematic does not accuratly reflect what is happening on the PCB,

[JustMe]

3 batteries. 4.5v

But I put the 5v in quotes because the schematic shows that the 4.5v joins the 5v line

[Andrew Neil]

Shall I be pedantic and say it's 3 cells forming a battery of 4.5V ... ?

:smirking_face:

[Andrew Neil]

It's a long time since I did it, but it certainly did run from the battery.

But I think I only tried on battery after making all of the mods to minimise power - so maybe there's something in there that's actually required for running on battery ... ?

Have you tried debugging with an external ST-Link (or other debug probe) while running from battery?

[JustMe]

Not yet. At the moment I am not running the original firmware. At first I thought it might be firmware related but after inspecting the schematic there does not seem to be anything that would let the firmware know which usb plug the power is coming from for example.

I think there must be a bridge or jumper which ST has forgotten to mention. My PCB still has all the jumper setting in their original locations.

I have done all my testing with it plugged in to power via the link usb plug. Yesterday was the first day I tried it with 3 cells 😉 powering it, only to discover it did not transmit