When a 3V cell battery is connected to the Electron over VBAT and GND, the Electron attempts to turn on and then goes into a fault mode with the RGB LED showing red.
I've found this information in the datasheet, but there is no link:
VBAT Supply to the internal RTC, backup registers and SRAM when 3V3 is not present (1.65 to 3.6VDC). The Pin is internally connected to 3V3 supply via a 0 ohm resistor. If you wish to power is via an external supply, you'll need to remove this resistor. Instructions to remove this resistor can be found here
Seems as though this may be expected behavior. If I want to remove the connection to 3.3V power, where are these instructions?
Just wondering @jvanier any updates on this? I’m having the same issue myself, and couldn’t find any addt’l info in the docs or any feature branches in on Github
VBAT Supply to the internal RTC, backup registers and SRAM when 3V3 is not present (1.65 to 3.6VDC). The Pin is internally connected to 3V3 supply via a 0 ohm resistor. If you wish to power is via an external supply, you'll need to remove this resistor. Instructions to remove this resistor can be found here
As for instructions, all you need to do is desolder the resistor located here. If you don't have a soldering iron, you can probably use some diagonal cutters to clip the resistor off of the board (please buy a soldering iron though). Measure continuity between VBAT and 3V3 to ensure the 0 ohms has been removed.
@beck through testing, I found a reason why VBAT should definitely be connected to 3V3. It's not absolutely necessary... but if you need your SRAM to be initialized on first power up, you should connect it as follows:
[1] Note: If VBAT is floating when powering up for the first time, SRAM remains uninitialized. When using this feature for Backup RAM, it is recommended to have VBAT connected to a 3V3 or a known good power source on system first boot. When using this feature for Extra RAM, it is recommended to jumper VBAT to GND to ensure it always initializes on system first boot.
So how are we supposed to use VBAT in production? It can’t be required that we manually desolder a component from every single electron to get Vbat working?
The design of the Electron requires a battery due to cellular instantaneous power requirements so given there will always be a battery, Particle tied VBAT to V3.3 through a zero ohm resistor. Since V3.3 is either supplied by the power input or the battery, this means that VBAT is normally powered correctly.
If you fail to remove the zero ohm resistor and try to use VBAT for you own purposes, then it can be a problem.
Well in our case we embed electron into our “motherboard” which has the capability of providing enough power and there would not be any battery attached so this creates kind of problem. Especially as we’re using SRAM for some important storage which needs to survive reboot.
And I don’t really feel good to start removing a single very small smd component during production as it introduces way too many possible errors to everything. So I guess we have to choose to either get rid of the 0ohm resistor or forget about using sram…
If you need this unsoldered, we might be able to give you trays of electrons with this jumper de-populated. I'll find out if that's something we can offer.
@tuxie sorry for the delay, would you please write into and start a dialog referencing this thread? I think that’s probably the right way to handle this to get you more specialized information.
Also when powering from VIN alone from a power supply, I have found that I’ve needed a large 470uF capacitor directly on VIN and GND pins of the electron. Without this the current spikes that the electron draws for communication can cause errors due to power supply transients. If your power supply is fairly close you may not require this, but it’s something you can test and/or provide a footprint for on your PCB.
and start a dialog referencing this thread? I think that’s probably the right way to handle this to get you more specialized information.