SLUSCU0I March 2018 – September 2020 BQ77915
The CHG and DSG FET drivers are designed to have fast switching time. Customers should select a proper gate resistor (RCHG and RDSG in the reference schematic) to set to the desired rise/fall time.
The CHG FET fall time is generally slower because it is connected to the PACK– terminal. The CHG driver will pull to VSS quickly when the driver is signaled to turn off. Once the gate of the CHG FET reaches ground or Vgsth, the PACK– will start to fall below ground, the CHG signal will follow suit in order to turn off the CHG FET. This portion of the fall time is strongly dependent on the FET characteristic, the number of FETs in parallel, and the value of the gate-source resistor (RGS_CHG).