1. The DC and CC pins are for controlling the charging and discharging FET. Are DC and CC pins both at high level during charging? Similarly, are they both at low level during discharging? If so, why do we need two control pins? It seems that one will do the job.
In the situation of normal battery charging and discharging, the voltage level of DC and CC are both high, such that the two MOSFETs are simultaneously conducting. If there is any over-discharging, over-charging, or over-current, one MOSFET can be turned off to stop the charging or discharging. Suppose that only the MOSFET at DC is used, the voltage at DC pin can be pulled low to stop discharging. However, in case of over-current, even pulling the voltage at DC low would not prevent the body diode of the MOSFET from conducting, therefore failing to protect the circuit.
2. PK+ and PK- are connected to a charger and load. It is said in the data sheet that, in case of over-voltage, the FET at the CC end will be shut down until the voltage is reduced. If the charger is disconnected at this moment, will the FET at the CC end be turned on immediately to supply power to the load?
Yes. As long as the over-voltage situation is resolved, the voltage at CC pin will become high, and the MOSFET will be conducting.
3. What is the maximum voltage supported by the charger? Is the FET at DC pin off during charging? I would like to know how the current flows through the chip during charging and discharging. If the DC end and CC end are both open during charging, wouldn't the voltage at VIN end be the same as the charging voltage? Will it be immediately determined that charging is complete?
The range of the power supply voltage of the DS2784 is 2.5V to 4.6V, which means that the voltage of the charger cannot exceed 4.6V, otherwise the DS2784 may be damaged. Both MOSFETs are open during charging and discharging, otherwise the current cannot flow into or out of the battery. During charging, the charging voltage will be pulled down by the battery after being applied to the battery, and it will gradually be increased along with the increase of battery capacity.