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 V
WAKEONLD
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 V
WAKEONLD
(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 may prevent the device from 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 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).
13.6 CONFIG_UPDATE Mode
The BQ76942 device uses a special CONFIG_UPDATE mode to make changes to the data memory settings.
If changes were made to the data memory settings while the firmware was in normal operation, it could result
in unexpected operation or consequences if settings used by the firmware changed in the midst of operation.
When changes to the data memory settings are needed (which generally should only be done on the customer
manufacturing line or in an offline condition), the host should put the device into CONFIG_UPDATE mode,
modify settings as required, then exit CONFIG_UPDATE mode. See the
BQ76942 Technical Reference Manual
for more details.
When in CONFIG_UPDATE mode, the device stops normal firmware operation and stops all measurements and
protection monitoring. The host can then make changes to data memory settings (either writing registers directly
into RAM, or instructing the device to program the RAM data into OTP). After changes are complete, the host
then exits CONFIG_UPDATE mode, at which point the device restarts normal firmware operation using the new
data memory settings.
SLUSE14B – DECEMBER 2020 – REVISED DECEMBER 2021
52
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