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Original question:

BQ78Z100: BQ78Z100 Sleep Mode and Current Draw

BQ78Z100: Battery can't get into SHUTDOWN mode when Vpack < Charger Present Threshold

Chen Jia
Intellectual 850 points
Part Number: BQ78Z100

Tool/software:

To whom it may concern:

We are using BQ78Z100 for a single cell battery, and noticed the fuel gauge can't get into SHUTDOWN mode when the cell voltage is lower than the SHUTDOWN threshold (2.5V), even Vpack (3V) < Charger Present Threshold (3300mV).

This special design could have 3V on the P+ terminal, but the battery is not charging (current = 0). Based on the BQ78Z100 tech reference, it should meet the voltage base shutdown conditions, but based on our test, the fuel gauge can't fall into SHUTDOWN mode. We also tried to increase the Charger Present Voltage to 3.6V, but it still didn't help.

Status        Condition                                                                                                           Action
Enable       Min cell voltage < Shutdown Voltage                                                                OperationStatus()[SDV] = 1
Trip            Min cell voltage continuous < Shutdown Voltage for   Shutdown Time             Turn DSG FET off 
Shutdown  Voltage at PACK terminal < Charger Present Threshold AND Current() ≤ 0     Send device into SHUTDOWN mode 

Could you help to check?

Thank you!

Chen

  • 0
    TI__Mastermind 27321 points

    Hi Chen,

    Can you send a log and gg file?

    I am thinking the [ Voltage at PACK terminal < Charger Present Threshold AND Current() ≤ 0 ] condition is not meeting. 

    Can you try removing any voltage at the pack pin if there's one? Let's test this with a 0V at Pack pin. 

  • 0 in reply to Jose Couso
    Intellectual 850 points

    Hello Jose:

    After removing the voltage on the P+, the IC can fall into SHUTDOWN mode as expected. Here is the GG file and SREC file.

    SW01414_1R05.zip

    The settings here:

    Power Shutdown Charger Present Threshold 3000 mV
    Power Sleep Sleep Current 10 mA

    I am not sure which log file you are looking for. Could you be more specific?

    Thank you very much!

    Chen

  • 0 in reply to Chen Jia
    Intellectual 850 points

    Hello Jose:

    BTW, we already tried to change the "Charger Present Threshold" to 3300mV, but the IC still can't fall into SHUTDOWN.

    Thanks.

    Chen

  • 0 in reply to Chen Jia
    TI__Mastermind 27321 points

    Hello Chen,

    So we know the device can enter shutdown after you remove the voltage on PACK pin. 

    When you have the charger attached, are you at least meeting the below two conditions?
    That is, SDV sets and DSG FET turns off?

    For this to work properly, the voltage at the PACK pin needs to drop below the Charger Present threshold after the FETs are disabled. If it doesn’t, the device might interpret that a charger is still present or some residual voltage is messing with the logic, and abort the shutdown process, reverting to normal operation.



    Threshold Setting    : 3000 mV is the default Charger Present threshold, which is reasonable for a 2-cell Li-ion pack (like yours, given 8.24 V fully charged). But if your system has a charger or load that keeps the PACK pin above this, you could try raising the threshold temporarily (say, to 5000 mV) to see if it helps the shutdown stick. Just don’t leave it too high for normal operation, as it might misdetect chargers.