Battery Stops Charging at 4.0 V (Expected 4.2 V Termination, 20% Termination Current)

[mhni]

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.

Setup details:

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

• Configured charge current: 800 mA

• Termination voltage: 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

Issue:
The battery stops charging around 4.0 V, even though the termination voltage is set to 4.2 V. Once the battery voltage reaches ~4.0 V, the charging current drops close to zero, and charging does not continue to 4.2 V.

Questions:

1. Could any internal safety or thermal mechanism cause early termination near 4.0 V?

2. Does disabling NTC monitoring affect charging accuracy or limit the termination voltage?

3. Are there specific status bits or event registers I can read to determine why charging stops early?

4. Could voltage drops on VBUS or board-level limitation cause this behavior?

5. Are there additional parameters (such as recharge threshold or termination comparator accuracy) that could affect this?

Any guidance on ensuring proper full-charge behavior up to 4.2 V would be appreciated.

Thank you,

[mhni]

Thank you for the clarification.
Could you please provide your final suggestions or best practices to achieve accurate charging termination at 4.2 V?
I’d like to ensure consistent performance similar to the intended termination voltage behavior.

[Tomi Koskela]

Hello, 

Note the termination current is typically specified in the battery datasheet. This is for safety reasons and avoiding overcharging the battery. So if you will follow the battery manufacturer guidance for charging the battery you will see this voltage step between the termination voltage and the cell voltage when charging has ended. If you want to get smaller termination current (and get closer to the termination voltage when charging stops) you can adjust the charging current lower through TWI. Unfortunately the lowest termination current is 10% of the charging current, so to get lower you would have to change the charging current itself. 

[mhni]

Hello,

Thank you for the detailed information.
As the termination current is fixed at 10% of the charging current, would it be possible to automatically reduce the charging current after the battery reaches about 80% SoC to achieve a lower termination current and a termination voltage closer to 4.2 V?

[Tomi Koskela]

Hello, 

We don't have that kind of automatic behavior in the PMIC if that is the question. But it could be done with SOC/software control if needed. 

[mhni]

Hello,

I have tried increasing the termination voltage to 4.30 V to reach the expected battery voltage of 4.20 V.
However, every time on the first power-on, the charging stops at around 4.13 V.
After re-enabling charging, the battery then charges up to 4.20 V as expected.

This behavior is observed using the nPM1300 EV Kit with the nPM PowerUP application.
Could you please share your suggestions or possible reasons for this behavior, and how it can be adjusted so the charging reaches 4.20 V on the first cycle?