Radxa Zero 3W - Plan & Questions for Direct Battery Connection & PMIC (RK817) Features

#1

Hi Radxa Community and Team,

I’m currently working on a compact commercial IOT project and considering using the Radxa Zero 3W, and I’m planning to integrate a Li-Ion/Li-Po battery. My goal is to leverage the full onboard power management capabilities of the RK817-5 PMIC that the Zero 3W utilizes, specifically for direct battery connection, charging, power path management, and hopefully, the fuel gauge features.

I’ve been reviewing both the RK817 datasheet and the Radxa Zero 3W V1.12 schematics, particularly Sheet 21 (“Power PMIC”), to understand how these features are implemented. My intention is to solder a battery directly (or via an appropriate connector to pads if available) to utilize these integrated functions, hoping to create a more compact solution than using external power management boards (like a PowerBoost that I was using with a Raspberry Pi).

From theRK817 datasheet, it’s clear the PMIC offers:

  • An integrated switch-mode Li-Ion battery charger (up to 3.5A).
  • Intelligent power path management.
  • An accurate battery fuel gauge using voltage and current ADCs.
  • An integrated RTC.

I’m currently examining the Zero 3W schematics to identify:

  • The best physical connection points for a battery (e.g., pads or connector linked to RK817 BAT pins 56/57).
  • The implementation of the charging circuit around the RK817’s MIDU/BOOST (pin 54) and USB/OTG (pin 55) pins.
  • Connections for a battery thermistor via the TS/GPIO pin (pin 61).
  • The current sense resistor setup for the fuel gauge using SNSP (pin 62) and SNSN (pin 63).

My questions to the community and Radxa team would be:

  1. Are there recommended solder pads or an unpopulated connector footprint on the Zero 3W V1.12 PCB specifically intended for direct Li-Po battery connection to the RK817’s BAT pins? noticeably what is the “VCC_BAT+” on the schematics connected to pin 56,57
  2. Beyond the physical connection, are there any specific Device Tree overlay modifications or kernel configuration settings required to fully enable and utilize the RK817’s charger, power path, and fuel gauge features if they are not active by default in the official Radxa OS images for the Zero 3W?
  3. Has anyone in the community successfully implemented direct battery power with charging and fuel gauge monitoring on the Zero 3W using the RK817? Any tips, experiences, or recommended battery protection considerations would be greatly appreciated.
  4. Regarding the fuel gauge data (battery percentage, current, voltage), what’s the recommended way to access this information from userspace Linux

I’m aiming for a clean and reliable integration and am happy to share my progress and findings with the community as I move forward with this. Any guidance, advice, or shared experiences would be invaluable!

Thanks,