4.2V on the VUSB+ pin are not enough to charge the Li-Po battery?

[T1mS]

Hey all,

I have a problem with the build in battery charger. My boron is connected to a main board. From the main board i receive over UART data packages. There are additional 5V and GND connections between them. On the 5V line is a diode, to make sure the main board can’t draw current from the battery which is connected to the boron. The problem now is, that after the diode only 4.2V are applied on the VUSB pin, which is not enough for the battery charger to charge the battery.

In the boron datasheet I couldn’t find a voltage range the charger at least needs?

Second question is, if I add a voltage divider after the 5V line to get 3.3V can I use this as an wakeup interrupt? So as soon as the main board get’s turned on, my particle will wake up to send the newest data?

Thanks in advanced.
Tim

[ScruffR]

You may want to go for a different diode with lower forward voltage (e.g. Schottky with 0.2V are the lowest you can typically get)

So as soon as the main board get’s turned on, my particle will wake up to send the newest data?

This seems like a call for a function that is considered undesired behaviour in this thread

Mesh Products in deep sleep wake on USB/VIN power state change

reading the data sheet for the nrf I found the following statement “When VBUS rises into its valid range while the device is in System OFF, the device resets and transitions to System ON mode”. Looking at the schematic the Vbus pin is directly connected to the vbus of both the usb and the nrf, so this will always wake the device (And feed back into the PC!) which begs to wonder why this was used instead of connecting it the vin side of the lipo charger after the protection diode. So to me looks…

[T1mS]

You may want to go for a different diode with lower forward voltage (e.g. Schottky with 0.2V are the lowest you can typically get)

So there is no alternative to manage this on software site with for e.g. the PMIC?
Will order some and check it out.

This seems like a call for a function that is considered undesired behaviour in this thread

Thanks for the link

[ScruffR]

BTW, when you power your device off of LiPo you will not see any voltage on VUSB.
So the risk of powering your main board off the LiPo is not actually an issue

Have a look at the block diagram and schematics
https://docs.particle.io/datasheets/cellular/boron-datasheet/#block-diagram
https://docs.particle.io/datasheets/cellular/boron-datasheet/#power-1

[T1mS]

But before I was using the diode the main board didn’t turned off by using it main switch. That’s a strange behavior i guess.

Another strange thing: the battery is unplugged and the board is connected to the 5V line and even when both systems are off the particle boron draws 10mA which will discharge the battery of the main board in a while. I have an STH31-D temperature sensor connected to the 3.3V pin of the boron, but when the boron is off there should not be any current draw, right?

[peekay123]

@T1mS, can you share schematics of the board? It is hard to advise without an understanding of your hardware configuration.

[T1mS]

@peekay123 , here you go. The micromatch is the port I connect to the main board.

The aim is to charge the boron battery whenever the main board is switched on and to use the extra battery otherwise.

[ScruffR]

I have an STH31-D temperature sensor connected to the 3.3V pin of the boron, but when the boron is off there should not be any current draw, right?

Even when the Boron is in sleep mode, the onboard regulators will not be switched off and hence anything feeding from the 3v3 pin will also be powered.

[T1mS]

So using one of the digital pins to feed the sensor would be one option? This way I could turn the voltage on before reading and off afterwards?

[ScruffR]

That should be an option.

[T1mS]

Hi @ScruffR, @peekay123

I have another question, is it possible to switch between the connected battery and the VUSB+ as the main power supply? My main board also has an battery which is going to discharge to quickly even if the boron is on sleep. I made a measurement of the current which is drawn from the battery (connected to the boron) while my main board supplies these 5V and its only around 9 microA. So the main current is drawn from the main board (40-70 mA). I already realized that my battery only gets charged when the main board is connected to a charger.

Best regards,
Tim