NPM1100 charging to 4.1v with VTERM fixed to VSYS

RE: NPM1100 charging to 4.1v with VTERM fixed to VSYS

Kyrre Aalerud — Mon, 12 Jun 2023 10:55:14 GMT

Investigating what can cause a 100mV reduction in VTERM lead us to identify the battery protection!

Vthigh_delta is 100mV and is the reduction applied to VTERM if battery is detected to be over 45v but below 60c. Due to earlier batterys not having a thermistor we did place the suggested 10k resistor on board similar to datasheet. However BOM error has caused this to still be placed in latest manufacture causing temperature interpretation to be very close to 45c. The error was not discovered until summer as temperature under appox 25-30c in room still leads to normal charging.

For those finding this later:
NPM1100 can reduce VTERM by 100mV if it thinks battery is between 45c and 60c.
Make sure your NTC connection is correct!

RE: NPM1100 charging to 4.1v with VTERM fixed to VSYS

Kyrre Aalerud — Mon, 12 Jun 2023 08:31:13 GMT

According to multiple articles including this ( https://www.powerstream.com/lithium-ion-charge-voltage.htm ) and our own tests we are lacking quite a large portion of capacity. (Which I assume we gain as cycle life.)

We have been using the MAX17263 to report voltage and capacity via coulomb counting and the numbers appear to align with what we read.

Since the VTERM can be changed at any time the use of VSYS or VBAT should not matter. Thus, is the reason for the low termination simply errata on old devices that should not have been used in manufacture?

RE: NPM1100 charging to 4.1v with VTERM fixed to VSYS

ketiljo — Mon, 12 Jun 2023 08:22:19 GMT

VTERM can be changed any time, including during charging. VBAT level is considered "logic high" for VTERM, so 4.2 V.

Due to the internal resistance in the battery, the voltage measured on the outside (VTERM) will be higher than the internal voltage on cell when the charger is operating. When charging ends, you will hence measure lower voltage than VTERM. In any case, the difference in the charged capacity of the battery when the end voltage is 4.1 V vs 4.2 V is very little. If you are experiencing poor capacity, this is not caused by VTERM.

The devices you have are rather old, and should not be used in production.

RE: NPM1100 charging to 4.1v with VTERM fixed to VSYS

Kyrre Aalerud — Fri, 09 Jun 2023 13:37:57 GMT

Sure, since it is basically from datasheet I do not think that is a problem.

My concern is the statement that VTERM is fixed and should only be changed in powerdown, while datsheet recommends using VSYS which comes up on powerup. I checked and DEC also does this.

What happens if VTERM connects to VBAT?

RE: NPM1100 charging to 4.1v with VTERM fixed to VSYS

ketiljo — Fri, 09 Jun 2023 13:21:29 GMT

Can you share your schematic please?