Use nPM1300 fuel gauge without charger

[timonsku]

I have a bit of an unusual use case where the nPM1300 is quite ideal but need to use an external charger for the battery instead of the internal charger. The nPM1300 fuel gauge works great for the application and I would like to avoid using a third component for that. Does the fuel gauge depend on the charger being active or can it be used independently?

The battery model would still be created with the nPM1300 EVK but the final application would use an external charger. The nPM1300 would be subjected to the charge voltage of the external charger but would not exceed the rating of the nPM1300 battery input.

[Tharaka]

Hi,

For the nPM1300 fuel gauge to operate correctly, all the battery current both charge and discharge must flow through the nPM1300 PMIC.

In your use case, since you're using an external charger, fuel gauging during charging is not supported, as the PMIC cannot monitor the charge current.

However, you can still use the fuel gauge during discharge mode, provided that:

• All discharge current passes through the nPM1300 PMIC, and
• No other loads or circuitry are connected directly to the battery.

As long as you properly initialize the fuel gauge after a full charge cycle using the external charger, fuel gauging during the discharge phase remains possible as long as the external charger is disconnected and all current paths are routed through the PMIC.

Regards,

Tharaka

[timonsku]

Could you elaborate what you mean with properly initialize? Is there something more specific that I need to tell the fuel gauge in this case? As in do we need to tell it that a charge cycle terminated to prime it correctly for discharge tracking?
Atm we just use the Zephyr integration and initialize the fuel gauge device once automatically at boot and then regularly call the fuel gauge update function as demonstrated in the samples.

The charger would stay physically connected but it would not keep charging intermittently during use and all discharge happens through the PMIC. The external charger would connect directly to the battery input so would be in parallel to the nPM1300 battery input. The charger itself enters a deep sleep and use effectively no meaningful amount of current (<1uA) while the device is in operation and not charging so its current consumption should not affect the system very meaningfully.

All in all it sounds like this would then work for our situation?

[Tharaka]

Hi

By "properly initialize," I mean that the fuel gauge should begin tracking from a known state-of-charge reference point—ideally, right after an event from your external charger that,  full charge cycle has completed and your external charger is in deep sleep state. So call the nrf_fuel_gauge_init() after that.

Fuel gauge initialization at boot is also required.

Based on everything you've described, your setup should hopefully work fine. Since this isn’t a typical use case (using an external charger alongside the PMIC fuel gauge), we recommend performing additional testing on your end to verify fuel gauge accuracy with your application.

Regards

Tharaka

[timonsku]

thanks for all the details. We will certainly perform comprehensive tests but that gives us confidence that we are not actively working against the system in theory.