Battery management system always in overcurrent mode.

[csrobertson63]

Hi Folks,

I am seeing an issue with AP9101CAK6-BVTRG1 Battery management system, and I am hoping you can give me new tips on things to try because I've been pulling my hair out on this for a few days.

Datasheet:https://www.diodes.com/assets/Datasheets/AP9101C.pdf

This is a very similar issue to these forum posts, both of which seem to have no solution:
https://www.eevblog.com/forum/projects/li-ion-protection-ic-too-protective-always-in-overcurrent-detect-mode/

https://www.reddit.com/r/AskElectronics/comments/8wmpsp/help_with_ap9101c_liion_protection_circuit_low/

I have chosen this BMS as it has auto power on mode which is needed in my application. The battery management system is designed on a PCB according to the reference design in the datasheet. The Mosfets used in the design are Texas instruments CSD16406Q3 (however I have used others as identified below), all other components are the same values as used in the data sheet.

This BMS also seems identical to the Ablic S-8250 (which is much harder to source) if that makes any difference.

Specifically the chip is the AP9101CAK6-BVTRG1 with Vdoc sense = 0.10v.

My design goals for the protection circuit are:
Undervoltage cutoff at ~2.8v
Overcurrent cutoff <= 1A
Normal current supply ~1mA, with a spike of about 800mA every  couple of hours.

My circuit is identical to the "Typical Applications Circuit" on page 2 of the datasheet. I'm using all of the recommended values as well for R1, C1, and R2. My load (A dummy 100ohm resistor) is across P+ and P-.

The current that I measure with just my load and battery is 34mA. Then when I hook up the protection circuitry, I measure a current of only 31mA.

From my calculations and those based off the quations in various data sheets and the previous forum posts, the voltage on the Vm pin should be at most

Vm = 34mA * (2* RDSon) = 0.35mV
RDSon = 5.2mOhm at vgs 4V

However, the value that im seeing, is ~130mV, as this is greater than the Vdoc value the BMS drives the DO pin low turning off the discharge fet. The output voltage drops to ~3.9V

Another weird thing I've noticed in testing is that if i turn the device on (using a battery or desktop PSU) with the load attached, the DO pin is low, and Vm = 130mv. If i then remove the load, the DO pin drives high and I get normal output (as expected with no load), however if i then re-apply the load, the DO pin remains high and the device works as normal.

I've tried 3 different MOSFETs with different RdsON values.
Here are the MOSFETs I have tried:
CSD16406Q3
CSD16301Q2
EFC8811R-TF

Its worth also noting I have tried multiple ICs and the identical chip without the auto power on mode and all work the same.

I have also tried multiple values for R2 from 0ohm through to 10kohm, these all changed Vm, all still over the 0.1V cutoff.

I can hook up my load and battery to the MOSFETs, and simply tie their gates to Vbat+, and the circuit performs as expected.

Also, I can take Vm pin and simply tie that to Vbat- and the circuit works as normal. This makes sense because Vm = 0v < 0.1v so it thinks there is no current flowing.

My Schematic is attached.

(I have tested with/without the additional Fuse, TVS diode and pmos on the input)

Any help is greatly appreciated. Please let me know what additional information you would like.

Thanks,
Cam.

[EAvMx]

Have you solved this?

I'm facing the exact same issue with the exact same chip version (BVTRG1)