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[FAQ] BQ76952: How does SHUTDOWN mode work?

Part Number: BQ76952

I would like to know more about SHUTDOWN mode.  

  • What methods can I use to enter SHUTDOWN mode?
  • How do I know if my device is in SHUTDOWN mode?
  • How do I WAKE the device from SHUTDOWN mode?
  • Hello,

    Below is an overview of SHUTDOWN mode that should answer the questions listed above:

    SHUTDOWN mode:

    SHUTDOWN mode is the lowest power mode of the device, and it is often used for shipment or long-term storage.  In this mode, internal logic is powered down, and all data memory (RAM) register information is lost.  While in SHUTDOWN, the device is completely disabled (including the internal, REG1, and REG2 LDOs).  The CHG, PCHG, DSG, and PDSG FETs are all disabled.  All battery protections are disabled, and no measurements are taken.  There is just a very low power ~5V internal rail that is driven onto TS2 through a ~4.6-MOhm resistor for WAKE detect.


    Entering SHUTDOWN mode:

    There are many different methods to initiate the SHUTDOWN sequence.  If any one of the conditions listed below are met—either a user action or fault—the device will initiate the SHUTDOWN sequence.

    Conditions to initiate SHUTDOWN sequence:

    • User action:
      • SHUTDOWN command given
      • RST_SHUT pin driven HIGH for ≥ 1s
    • Faults:
      • Low VBAT voltage (BAT pin voltage falls below VPORA – VPORA_HYS)
      • Low stack voltage (set by Power:Shutdown:Shutdown Stack Voltage)
      • Low minimum cell voltage (set by Power:Shutdown:Shutdown Cell Voltage)
      • Over-temperature
        • Set by Power:Shutdown:Shutdown Temperature
        • Set by Settings:Configuration:Power Config[OTSD]
      • Internal memory failure

    More information for condition thresholds and timing can be found in the Technical Reference Manual.

    If the SHUTDOWN sequence is initiated, and the TS2 pin remains LOW or the LD pin remains HIGH, then the device will not fully enter SHUTDOWN mode, and will instead be stuck in Soft SHUTDOWN.  Soft SHUTDOWN is a temporary state that the device transitions through when attempting to enter SHUTDOWN mode.  More details on Soft SHUTDOWN can be found in the Soft SHUTDOWN FAQ.

    After the SHUTDOWN sequence has been initiated, the device will wait for a delay of Power:Shutdown: FET Off Delay, then disable the protection FETs.  After a delay of Power:Shutdown:Shutdown Command Delay from when the SHUTDOWN command is first written, the device attempts to enter SHUTDOWN mode.  It will only be successful if the conditions for entering SHUTDOWN mode are met.

    Please note that the Power:Shutdown:Shutdown Command Delay should be set to a longer delay time than Power:Shutdown: FET Off Delay to ensure that the FETs will correctly turn OFF before the device enters SHUTDOWN mode.  To bypass the Power:Shutdown:Shutdown Command Delay, the user can send the SHUTDOWN() command twice while in either the UNSEALED or FULLACCESS mode.

    Determining if the BQ769x2 is in SHUTDOWN mode:

    To check if the device is in SHUTDOWN mode, the user can measure the voltage on the REG18 pin. If the device is in SHUTDOWN mode, then the pin will output 0V, otherwise the REG18 LDO will output 1.8V. 


    Exiting SHUTDOWN MODE:

    While in SHUTDOWN mode, TS2 will idle high with a weak pull-up of ~4.6Mohm.  To WAKE the device, the TS2 pin must be pulled to GND, or the LD pin must be pulled above ~1.45V.  Once this occurs, TS2 will stay around 0V weakly.  Upon waking from SHUTDOWN, the device will load OTP settings into the BQ769x2 device registers.  Any register settings that were not programmed into OTP will be reset to default upon WAKEUP.

    One exception to the typical WAKE procedure is SHUTDOWN caused by low VBAT voltage.  If voltage is brought up from below VPORA – VPORA_HYS, then the device will WAKE up.  Please note that the Power:Shutdown:Shutdown Stack Voltage must be above VPORA – VPORA_HYS , or the device will enter SHUTDOWN mode triggered by low stack voltage and can only be awakened by pulling the TS2 pin LOW or the LD pin HIGH.

    When the device is wakened from SHUTDOWN, it generally requires approximately 200-300ms 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.  Please see Table 16-2 from the Datasheet for more precise timing specifications:

    To combat inadvertent WAKEUP during SHUTDOWN mode, the BQ769x2 can also be configured to automatically re-enter SHUTDOWN mode after a period of time configured in Power:Shutdown:Auto Shutdown Time.  The BQ769x2 will only auto-SHUTDOWN if the device WAKES from SHUTDOWN mode without any valid communications occurring or any charge or discharge current detected.  These precautions prevent the device from entering SHUTDOWN mode in the case of intentional WAKEUP.

    For a summary of common methods used to transition between power modes, please see Figure7-1 from the Technical Reference Manual.

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