Hi !
I want to build a protection for the 3.6V Panasonic NCR18650B Li-ion cell, using the AP9101C chip. It has the following schematics...
But I don't understand how that duble mosfet switch works. From what I understand, when a MOSFET is OFF it conduct through its body diode in the reverse way. Lets imagine the followin scenario... The battery is charging and it enters in overcharge protection, so the Q2 will switch OFF. Now we start discharging the battery, while it has charging disabled. The curent from the battery plus (+) will go through load and reach the Q2 Source terminal. The MOSFET being OFF, the channel is blocked so the current will flow throug the body diode. Em I right ? But, I think that that diode isn't supposed to be used that way. So, how this schematics works if the only available path is through those diodes, but they are not supposed to by used in normal operation. I think somewhere is a misunderstanding...

 

It seems that AP9101C chip si no longer manufatured... So, if you have any other sugestions for a similar Li-ion cell protection, I am open.
In the "big picture" I am trying tu build an uninterruptible power supply with the output voltage anywhere in the range 2V-5V, backed up by a 3300mAh Li-ion battery with all protections and a 4.2V charger with 5V input.

 

I decided to go with this chip...
Can someone help me to understand how can I calculate the overcurrent protections ? My chip will be the "AD" variant which has +/-120mV threshold for charging and discharging overcurrent and 700mV for discharging short circuit... First off all I don't understand if both mosfet Rdson counts to those 120mV threshold or just one ? As It seems to me, it must count everything that is between their sources ( VSS to P- ). But that is not constant because both mosfets are ON in normal operation, and just one in fault condition. Is verry confusing... And then when one mosfet is OFF it isn't conducting through the inverse body diode that create a 0.7V in the voltage monitored that will exced the 120mV and trigger the protection even in normal operation ?

 

I decided to go with this chip...
Can someone help me to understand how can I calculate the overcurrent protections ? My chip will be the "AD" variant which has +/-120mV threshold for charging and discharging overcurrent and 700mV for discharging short circuit... First off all I don't understand if both mosfet Rdson counts to those 120mV threshold or just one ? As It seems to me, it must count everything that is between their sources ( VSS to P- ). But that is not constant because both mosfets are ON in normal operation, and just one in fault condition. Is verry confusing... And then when one mosfet is OFF it isn't conducting through the inverse body diode that create a 0.7V in the voltage monitored that will exced the 120mV and trigger the protection even in normal operation ?

Help with AP9101C Li-Ion protection circuit low voltage on MOSFET gates : r/AskElectronics



batteries - DW01 Over current Voltage? - Electrical Engineering Stack Exchange

Use It = V_overCurrent / (2 x Ron)

 

You need to divide the threshold voltage by the rdson of the two MOSFETs in series.

You can also use HY2116 or ABLIC chips.