SLUSE13A January 2020 – May 2021 BQ76952
SLEEP mode is a reduced functionality state that can be optionally used to reduce power dissipation when there is little or no system load current or charging in progress, but still provides voltage at the battery pack terminals to keep the system alive. At initial power up, a configuration bit determines whether the device can enter SLEEP mode. After initialization, SLEEP mode can be allowed or disallowed using subcommands. Status bits are provided to indicate whether the device is presently allowed to enter SLEEP mode or not, and whether it is presently in SLEEP mode or not.
When the magnitude of the CC1 Current measurement falls below a programmable current threshold, the system is considered in relax mode, and the BQ76952 device will autonomously transition into SLEEP mode, if settings permit. During SLEEP mode, comparator-based protections operate the same as during NORMAL mode. ADC-based current, voltage, and temperature measurements are taken at programmable intervals. All temperature protections use the ADC measurements taken at these intervals, so they will update at a reduced rate during SLEEP mode.
The BQ76952 device will exit SLEEP mode if a protection fault occurs, or current begins flowing, or a charger is attached, or if forced by subcommand, or if the RST_SHUT pin is asserted for < 1-sec. When exiting based on current flow, the device will quickly enable the FETs (if the CHG FET was off, or the DSG FET was in source follower mode), but the standard measurement loop is not restarted until the next 1-sec boundary occurs within the device timing. Therefore, new data may not be available for up to ≈1-sec after the device exits SLEEP mode.
The coulomb counter ADC operates in a reduced power and speed mode to monitor current during SLEEP mode. The current is measured every 12 ms and, if it exceeds a programmable threshold in magnitude, the device quickly transitions back to NORMAL mode. In addition to this check, if the CC1 Current measurement taken at each programmed interval exceeds this threshold, the device will exit SLEEP mode.
The device monitors the PACK pin voltage and the top-of-stack voltage at each programmed measurement interval. If the PACK pin voltage is higher than the top-of-stack voltage by more than a programmable delta and the top-of-stack voltage is less than a programmed threshold, the device will exit SLEEP mode. The BQ76952 device also includes a hysteresis on the SLEEP mode entrance, in order to avoid the device quickly entering and exiting SLEEP mode based on a dynamic load. After transitioning to NORMAL mode, the device will not enter SLEEP mode again for a number of seconds given by the hysteresis setting.
During SLEEP mode, the DSG FET can be driven either using the charge pump or in source-follower mode, as described in Section 11.4. The CHG FET can be disabled or driven using the charge pump, based on the configuration setting.