BQ76940EVM: Load Detection

Hi Joao,
The load detection circuit is a comparator and pull down on the CHG pin. If there is a sufficient load it will prevent the pull down from bringing CHG below the comparator threshold. With a load that is removed the pull down will eventually pull CHG below the comparator threshold indicating the load is removed. Connecting the charger where a load has been removed should immediately drop the PACK- below the comparator threshold indicating the load is removed, but it is not specifically a charger detection. If the load and charger are connected simultaneously the one with the greater current capability will win.
The bq76940 does not have a hardware over current charge (OCC) protection. When used with the bq78350(-R1) on the EVM and the charge current from regenerative braking exceeds the OCC thresholds it will protect. If the regenerative braking current events are above the threshold but below the delay, or if the gauge is not used, the cell voltage will be raised and may eventually reach an OV.

The bq78350-R1 is designed for series FETs. The bq78350-R1 will generally keep both FETs on unless there is some fault or condition to turn off a FET. The technical reference manual (TRM) for the part will describe various features and configuration. One behavior which is built in but not noted is FET body diode protection. If current is detected flowing through a disabled FET body diode, the FET will turn on. For example if the battery has the charge FET off due to a high temperature but discharge current is detected, the charge FET will be turned on again while that current is flowing to prevent heating of the FET.
The bq76940 and bq78350-R1 are designed for battery protection and gauging, and do not have features for system current control. The gauge has the KEY enable option to prevent discharge if the signal is disabled, but the body diode protection will turn on the discharge FET as noted. If the system allows both charger and load applied simultaneously with the key disabled, while the current flows into the battery the discharge FET is on. If the load exceeds the charger capability current could be drawn from the battery while it recognizes the discharge current and turns off the discharge FET again. If the load (motor) controller drops out and charge resumes the system could cycle. A better solution is to have the system recognize that the charger is attached and prevent current flow to the load or disable load controllers which could exceed the charger. For example it might be desired to enable bicycle instrumentation while charging but prevent motor and/or lighting operation, but those are controls which need to be implemented in the system rather than the battery.
If an MCU is used to control the bq76940 split FETs can be used but the load present will not work and each path will not be protected against current in the opposite direction. This is undesirable in situations such as if a charger becomes a load when off or regenerative braking in an electric bicycle where the battery could not prevent overcharging throught the discharge path.