[FAQ] BQ76952: What is the Soft SHUTDOWN state?

Hello,

The answers to these questions and more information on Soft SHUTDOWN can be found below:

Soft SHUTDOWN:

When attempting to enter SHUTDOWN mode, some users may get stuck in Soft SHUTDOWN.  Soft SHUTDOWN is a temporary state that is entered if either the TS2 pin is held LOW, or the LD pin is held HIGH after the SHUTDOWN sequence is initiated.  If the user attempts to enter SHUTDOWN mode, but the REG18 pin is outputting 1.8V instead of 0V, then the device is not in SHUTDOWN mode and may be in Soft SHUTDOWN.  The device will stay in the Soft SHUTDOWN state until both of these conditions are resolved. 

• LD: In Soft SHUTDOWN where the LD pin has been held HIGH, the protection FETs are disabled, but serial communication is still enabled. The REG1 and REG2 LDOs are still enabled.  To transition from the Soft SHUTDOWN state to SHUTDOWN mode, the device will wait until the LD pin falls below the V_WAKEONLD level, then it will transition into SHUTDOWN.  To transition from Soft SHUTDOWN to NORMAL mode, allow the LD pin to fall below the V_WAKEONLD level, then raise the LD pin above V_WAKEONLD level through charger attach.  Alternatively, perform a partial RESET by asserting the RST_SHUT pin HIGH for < 1s.

NORMAL mode --> LD Soft SHUTDOWN --> SHUTDOWN mode

NORMAL mode --> LD Soft SHUTDOWN --> NORMAL mode

• TS2: If Soft SHUTDOWN is caused by TS2 being held LOW (often by a thermistor), then the FETs will be disabled, protections and measurements will be stopped, and serial communication is disabled.  The REG1 and REG2 LDOs are disabled. To exit Soft SHUTDOWN due to the TS2 pin being LOW, perform a partial RESET to transition the device into NORMAL mode (see the RESET FAQ for more information).

NORMAL mode --> TS2 Soft SHUTDOWN --> NORMAL mode

The most common reason for accidentally entering Soft SHUTDOWN mode is due to circuitry placed on the TS2 pin.  Placing a thermistor on the TS2 pin will directly pull the pin LOW, causing Soft SHUTDOWN, but even circuitry that does not pull TS2 directly to GND can cause issues.  This is because the TS2 pin’s internal pull-up to 5V is very weak, so any small leakage paths in the circuitry attached to the TS2 pin can prevent SHUTDOWN by pulling the pin down.  Even 1µA of leakage current can cause the device to become stuck in Soft SHUTDOWN.

Since the TS2 pin must be pulled HIGH via the BQ769x2’s internal pull-up to enter SHUTDOWN mode, if the user wants to place a thermistor on the TS2 pin and does not intend on using SHUTDOWN mode, then they should program the SHUT_TS2 bit to 1.  This will ensure that the device does not attempt (and fail) to enter SHUTDOWN mode.  The device will instead enter a low-power state and wait for a rising edge on the LD pin to transition into NORMAL mode.

• Both LD and TS2: If the SHUTDOWN command is given while TS2 is pulled LOW to GND and LD is pulled HIGH, then the device will enter LD Soft SHUTDOWN (communication is still enabled, the SD_CMD bit is set, and the device is waiting for the LD pin to go LOW to transition into SHUTDOWN mode). If the voltage is then removed from the LD pin during LD Soft SHUTDOWN, then the device transitions into TS2 Soft SHUTDOWN (all communication is lost, but the REG18 pin has 1.8V on it) since the TS2 pin is still pulled LOW.

If the device is in LD Soft SHUTDOWN, with the LD pin pulled HIGH and TS2 pulled LOW, and the LD pin remains HIGH while the TS2 pin transitions from LOW to HIGH, then the device will remain in LD Soft SHUTDOWN.  If the LD pin is then allowed to go LOW after the TS2 pin has transitioned HIGH, then the device will enter SHUTDOWN mode.

In short, the LD pin being asserted HIGH takes precedence over the TS2 pin being asserted LOW.  Please see the flowchart below for more information on determining device mode based on LD and TS2 pin states:

LD and TS2 Soft SHUTDOWN Flowchart

For information on normal SHUTDOWN mode, please see the SHUTDOWN FAQ.

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