SLUUBY1B December 2020 – April 2022 BQ76942
SHUTDOWN mode is the lowest power mode of the BQ76942, which can be used for shipping or long-term storage. In this mode, the device loses all register state information, the internal logic is powered down, the protection FETs are all disabled, so no voltage is provided at the battery pack terminals. All protections are disabled, all voltage, current, and temperature measurements are disabled, and no communications are supported. When the device exits SHUTDOWN, it will boot and read parameters stored in OTP (if that has been written). If the OTP has not been written, the device will power up with default settings, and then settings can be changed by the host writing device registers.
Entering SHUTDOWN mode involves a sequence of steps. The sequence can be initiated manually by sending the 0x0010 SHUTDOWN() subcommand twice in a row within a 4-s time window if the device is SEALED. The subcommand is only required to be sent once if in UNSEALED or FULLACCESS modes. If this subcommand is sent twice in a row while the device is in UNSEALED or FULLACCESS modes, the delays associated with the sequence are skipped. The device can also be configured to enter SHUTDOWN mode automatically based on the top of stack voltage or the minimum cell voltage. If the top-of-stack voltage falls below Power:Shutdown:Shutdown Stack Voltage or if the minimum cell voltage falls below Power:Shutdown:Shutdown Cell Voltage, the SHUTDOWN mode sequence is automatically initiated. The shutdown based on cell voltage does not apply to cell input pins being used to measure interconnect, based on settings in Settings:Configuration:Vcell mode.
While the BQ76942 device is in NORMAL mode or SLEEP mode, the device can also be configured to enter SHUTDOWN mode if the internal temperature measurement exceeds Power:Shutdown:Shutdown Temperature for Power:Shutdown:Shutdown Temperature Delay seconds.
When the SHUTDOWN mode sequence has been initiated by the 0x0010 SHUTDOWN() subcommand or the RST_SHUT pin driven high for 1 second, the device will wait for Power:Shutdown:FET Off Delay then disable the protection FETs. After a delay of Power:Shutdown:Shutdown Command Delay from when the sequence begins, the device will enter SHUTDOWN mode (so Power:Shutdown:Shutdown Command Delay should be set longer than Power:Shutdown:FET Off Delay). However, if the voltage on the LD pin is still above the VWAKEONLD level, shutdown will be delayed until the voltage on LD falls below that level. Note: when SHUTDOWN mode is initiated in this manner, the device will first transition to NORMAL mode and will block entrance to SLEEP mode. If the FETs were initially off (such as if the device was in DEEPSLEEP mode) and Power:Shutdown:FET Off Delay = 0, the FETs will remain off. However, if Power:Shutdown:FET Off Delay > 0, the FETs may be enabled (if not blocked) upon entering NORMAL mode, then disabled after the Power:Shutdown:FET Off Delay. If this is not preferred, the host can send the 0x0095 ALL_FETS_OFF() before entering DEEPSLEEP mode, then can send the 0x0096 ALL_FETS_ON() when exiting DEEPSLEEP mode.
While the device is in SHUTDOWN mode, a ≈5-V level is provided at the TS2 pin with high source impedance. If the TS2 pin is pulled below VWAKEONTS2, such as by a switch to VSS, or if a voltage is applied at the LD pin above VWAKEONLD (such as when a charger is attached in series FET configuration), the device will exit SHUTDOWN mode. Note: if a thermistor is attached from the TS2 pin to VSS, this will prevent the device from ever fully entering SHUTDOWN mode.
As a countermeasure to avoid an unintentional wake from SHUTDOWN mode when putting the BQ76942 device into long-term storage, the device can be configured to automatically reenter SHUTDOWN mode after Power:Shutdown:Auto Shutdown Time minutes if the device boots from SHUTDOWN mode without any valid communications occurring or any charge or discharge current detected. This feature is disabled by default, so it is necessary to program it enabled in OTP to ensure it is enabled when an unintentional wake occurs. It also will not take effect after a watchdog reset has occurred. See Power:Shutdown:Auto Shutdown Time for more details.
The BQ76942 device performs periodic memory integrity checks and will force a watchdog reset if any corruption is detected. To avoid a cycle of resets in the case of a memory fault, the device will enter SHUTDOWN mode rather than resetting if a memory error is detected within Power:Shutdown:RAM Fail Shutdown Time seconds after a watchdog reset has occurred.
When the device is wakened from SHUTDOWN, it requires approximately 200 ms–300 ms (if Settings:Permanent Failure:Enabled PF A[CUDEP] is not enabled) for the internal circuitry to power up, load settings from OTP memory, perform initial measurements, evaluate those relative to enabled protections, then to enable FETs if conditions allow. This can be much longer if [CUDEP] is enabled, depending on its associated delay setting in Permanent Fail:CUDEP:Delay.
The BQ76942 device integrates a hardware overtemperature detection circuit, which determines when the die temperature passes an excessive temperature of approximately 120°C. If this detector triggers, the device will automatically begin the sequence to enter SHUTDOWN if the Settings:Configuration:Power Config[OTSD] configuration bit is set.
If the shutdown sequence has been initiated, but the TS2 pin is held below VWAKEONTS2, or the voltage at the LD pin is above VWAKEONLD, then the device will stay in a "soft shutdown" state until the TS2 pin voltage is no longer below VWAKEONTS2, and the LD pin voltage is below VWAKEONLD. While in "soft shutdown," FETs are disabled, protections and measurements are stopped, and serial communication is disabled. The device will exit "soft shutdown" if the LD voltage was allowed to first fall below VWAKEONLD, then was raised above VWAKEONLD by a charger being attached, if the RST_SHUT pin is transitioned from low to high, or the conditions allow the device to continue into SHUTDOWN mode.