[solved] How to use VBAT on Electron?

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?

Thanks for letting us know. A revision to the Electron datasheet with this information is in the works and will be posted shortly.

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

Thanks for reaching back. I’ll check with another Particle engineer who knows more about the Electron hardware.

Hey guys, looks like you found the note about the connection of VBAT and 3V3 on the Electron. From here: https://docs.particle.io/datasheets/electron-datasheet/#pin-markings-

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

While some info is in the Electron Datasheet, it’s obviously not enough and we intend on adding more of a description for the next revision of the datasheet. See known errata here: https://github.com/spark/docs/issues/19

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.

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Thanks @BDub!

Awesome thanks @BDub. Just curious, what’s the purpose of connecting 3v3 to Vbat in the first place?

@beck, STMicro recommends the connection when VBAT is not in use. :grinning:

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@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:

https://docs.particle.io/reference/firmware/electron/#backup-ram-sram-

[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.

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Great, thanks for the heads up!

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.

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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…

(never mind, I misread the previous comment)

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.

You can actually power the Electron from VIN without a battery as long as you supply enough voltage and current. The requirements are in the datasheet, 5V @ 2A on VIN https://docs.particle.io/datasheets/electron-datasheet/#vin

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Thanks @BDub that would be awesome option!

@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.

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