MP2760 charge termination behavior

Good morning.
I integrated the MP2760 charge controller into my 5800mAh 4s2p lithium battery pack.
I’m noticing strange behavior, especially at the end of the charge.

In the following image the graph of the electrical variables acquired by the chip during a typical charging process.

The things I can’t understand are the following:

  1. because the system voltage is always lower than the battery voltage while the opposite is indicated in the datasheet.
  2. because at the end of the charge these voltages suddenly go from the end of charge value of 16.8V to around 17.3V sometimes causing an over-voltage warning.
  3. because at the end of charge the value of the CHG_STAT bits in the status register become 0b111 which does not seem to be a valid value from the datasheet.
  4. because at the end of charge the input and battery currents have a short peak at a value similar to that of DC charging mode.

In the following image the electrical diagram of the charging and gauging part.

The following list shows the configuration of the MP2760 registers:
REG0Eh: Configuration register 0: 0x0190
REG0Fh: Configuration register 1: 0xB242
REG10h: Configuration register 2: 0x0614
REG11h: Configuration register 3: 0x61A8
REG12h: Configuration register 4: 0x3473

I can’t understand what I could have done wrong.
Can someone help me, please?

Regards,
Christian.

Christian,

have you checked, that the set charge termination voltages do correspond with the LiIon battery type you use?
What if you set the charge termination voltage lower than the max. the battery tolerates?
Have you tried a different cell type from a different vendor?
Have you disabled trickle charge?

BR

Hi Klaus,
in the battery pack datasheet the termination voltage has been declared at 16,8V +/- 1%, see folloving image.

image

But in the PANASONIC cell datasheet was declared at 4,15V (16,6V), see following image.

image

Surely setting the end-of-charge voltage to a lower value is tolerated by the battery, it’s just a question of how completely you want to charge the battery.
Since I can’t completely eliminate the Trickle charging current, I set it to the minimum of 50mA.
In the following images, currents and voltages can be seen in detail at the moment of the end of the battery charge.
This is the one with the end-of-charge voltage set at 16,6V:

While this is the one with the end-of-charge voltage set at 16,0V:

I really don’t know what happens after the CV loading phase, when the CHG_STAT registers take on an unexpected value of 7 and charging resumes when it should have ended…
It’s true, in this way I managed to lower the end-of-charge voltage, but I didn’t understand why!
I don’t know what is stopping this further charging phase.
Do you think the problem is due to the BMS of this particular battery pack?
In the next few days I will test the charger with a battery pack from another manufacturer.
Regards
Christian.