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BQ40Z50: Behavior when awakened from sleep/shutdown to normal (FETs, current, charging, etc.)

Jason Muhammad
Prodigy 130 points
Part Number: BQ40Z50

I cannot find a simple clear description of what BQ40Z50 does when it is awakened. Here are some questions I have questions about BQ40Z50 when it is awakened from sleep/shutdown by applying voltage to PACK (pin 27). The example is when end product has a button that applies B4+ of a 4-cell system to PACK through 10k resistor (like Figure 17 of TI document SLUA660A):

1) When the BQ40Z50 is awakened via external pushbutton and is a load attached to PACK+ and PACK- (negative of the system where sense resistor is), what does the BQ40Z50 do? ie how does it measure current if the DSG FET is open? Does it periodically wake up, close the DSG FET, measure then if no current go back to sleep? I cannot find the how or the sequence of events upon wakeup.

2) When the BQ40Z50 is awakened via external pushbutton and there is NO load or charger attached to PACK+ and PACK- (negative of the system where sense resistor is), what does the BQ40Z50 do?

I cannot find anywhere in any BQ40Z50 document where it describes the exact operation of the FG in these situations...it's like it assumes that it is obvious or well known to everyone.

TI datasheet SLUSCS4A for BQ40Z50-R2, section 8.4 Device Functional Modes says "The bq40z50-R2 has a wake function that enables exit from SLEEP mode when current flow or failure is detected." but how does current flow from cells if DSG and CHG FET is open? When does DSG FET close?

TI tech ref SLUUBK0B, section 5.3.4 Wake Function says "The bq40z50-R2 device can exit SLEEP mode if enabled by the presence of a voltage across SRP and SRN." How does current flow?

  • 0
    TI__Genius 12215 points

    Hi, Jason

        The Sleep mode and shutdown are 2 different low power modes. shutdown mode can be simply thought as power off mode, the internal power supply of the gauge is turned off, when the gauge is awakened from this mode, it undergoes power cycle, and the internal state including CHG DSG FET Statuses will be initialized according to the dataflash configuration and voltage, current, temperature detected by the gauge.

        For example if the NR bit is set and no safety bits are set, then the FETs would be on, however, if the NR bit is clear and SYSPRES pin is detected high, then the FETs will be open, even a load is attached to Pack+ and Pack-, no current would flow through the load

        Sleep mode is another low power mode, the FET status in sleep mode can be configuration in the dataflash. It is possible for the FETs to be on and gauge detect a current when load is applied. The internal power to the gauge is still on, but the gauge has lowered down it clock frequency and diminished its activity to minimum. 

        In Sleep mode. The interrupt can still trigger the gauge, the voltage on SRN and SRP(either by applying a voltage across SRN and SRP or apply a load to the PACK+ and PACK-) can launch an interrupt to the gauge and wakes up the gauge from sleep mode