SLUUCF2C January 2021 – May 2022 BQ769142
The BQ769142 device includes predischarge functionality, which can be used to reduce inrush current when the load is initially powered, by first enabling a high-side PDSG PFET (driven from the PDSG pin) with series resistor, which enables the load to slowly charge. If PREDISCHARGE mode is enabled, whenever the DSG FET is turned on to power the load, the device will first enable the PDSG FET, then transition to turn on the DSG FET and turn off the PDSG FET. PREDISCHARGE mode is enabled when Settings:FET:FET Options[PDSG_EN] is set.
When PREDISCHARGE mode is activated, the device remains in this mode until either a timeout is reached, or the voltage at the LD pin rises to within a programmable delta of the top-of-stack voltage, or both. The timeout can be set from 10 ms to 2550 ms in steps of 10 ms, using Settings:FET:Predischarge Timeout. If the timeout is set to 0, then the device does not use a timeout and exits PREDISCHARGE mode when the voltage condition is met. The voltage delta is programmable from 10 mV to 2550 mV in steps of 10 mV, using Settings:FET:Predischarge Stop Delta. If the voltage delta is set to 0, the device does not use a voltage condition and exits PREDISCHARGE mode based on the timeout.
If the Settings:FET:FET Options[PDSG_EN] bit is set and the DFETOFF or BOTHOFF signal is asserted, the DSG and PDSG FETs are disabled, but the device is initially blocked from entering SLEEP mode (if already in SLEEP mode, the device returns to NORMAL mode when the signal is asserted). SLEEP mode can again be allowed if the host sends the DSG_PDSG_OFF() or ALL_FETS_OFF() subcommand, or a protection fault occurs (such as a Host Watchdog Fault or an OTF fault).