SLUSE14A December 2020 – February 2021 BQ76942
SHUTDOWN mode is the lowest power mode of the BQ76942 device, 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 through the serial communications interface. 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 a programmed stack voltage threshold, or if the minimum cell voltage falls below a programmed cell voltage threshold, 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.
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 a programmed temperature threshold for a programmed delay.
When the SHUTDOWN mode sequence has been initiated by subcommand or the RST_SHUT pin driven high for 1-sec, the device will wait for a delay then disable the protection FETs. After the delay from when the sequence begins, the device will enter SHUTDOWN mode. 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.
While the device is in SHUTDOWN mode, a ≈5-V voltage is provided at the TS2 pin with high source impedance. If the TS2 pin is pulled low (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.
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 a programmed number of minutes.
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 a programmed number of seconds after a watchdog reset has occurred.
When the device is wakened from SHUTDOWN, it generally requires approximately 200 ms–300 ms 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 depending on settings.
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 automatically begins the sequence to enter SHUTDOWN (if this functionality is enabled through configuration).