Mikroe nPM1300 PMIC Click – Incorrect Charging Behavior (Stops at 4.0 V and CV Mode Starts on First USB Plug-In)

[mhni]

Description:

Hello Nordic team,

I’m using the Mikroe nPM1300 PMIC Click Board (based on the Nordic nPM1300 PMIC) with an ESP32 over I²C to charge a Li-ion battery.

I am observing two issues related to the charging behavior.

Setup details:

• Battery: 3.7 V nominal, 950 mAh Li-ion

• Configured charge current: 800 mA

• Termination voltage (VTERM): 4.20 V

• Termination current: 20% of charge current (~160 mA)

• VBUS current limit: 1500 mA (set manually via I²C)

• NTC monitoring: Disabled

• Power source: 5 V adapter connected to VBUS
• Communication: I²C via ESP32 MCU

Issue  – First USB connection starts in constant-voltage (CV) mode:

When the board is powered for the first time and a battery (~3.6–3.8 V) is connected, the charger immediately enters CV mode instead of constant-current (CC) mode.
If I remove and reconnect the USB power, charging starts correctly in constant-current mode and later transitions to CV mode as expected near 4.2 V.

Questions:

1. Is there a known condition where the nPM1300 starts in CV mode after power-up?

2. Should I trigger a specific charger task (e.g., TASKCHARGERSTART) after VBUS connection to properly initialize the charge cycle?

3. Could the VBUS current limit or ADC enable sequence affect the initial charging phase detection?

4. Are there recommended register writes or startup sequences to ensure proper CC-to-CV transition behavior?

[Tomi Koskela]

Default termination voltage is 3.6V and it could be the initialization is not done in correct order. You need to first configure the charger and after that activate charger with the BCHGENABLESET. Note that with the VBUS current limiter you need to call TASKUPDATEILIMSW to activate the new setting and it will be reset back to default when you unplug/plug USB again.