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Original question:

BQ27Z746: bq27z746 - SLEEP and SHELF modes activation

BQ27Z746: Shutdown Mode

Sobin Sebastian
Prodigy 180 points
Part Number: BQ27Z746
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

Hello Team,

We are using BQ27Z746 in our smart hand held thermometer. We have calibrated this devices with proper configurations, learning cycle, Chem id etc.

Recently we observed that the the fuel gauge has its CHG and DSG  FETs disabled when the device is not used , means MCU is off but Charger IC and regulators are ON and a very less current approx. 10-15uA is sourced from battery through Fuel Gauge. This is observed when this low power mode is continued for 2.5 days or more. The battery cannot be charged or Discharged in this state.

But when the Fuel Gauge is power cycled the Fuel gauge enables its CHG and DSG FETs.

Why is Fuel Gauge showing this behavior, are we missing some configuration ?  Is this observation expected and how to solve this.

.

Any suggestion helps

Thanks,

Sobin.

  • 0
    TI__Mastermind 26135 points

    Hello Sobin,

    The fetes are open during shutdown mode, and this is down to save on power.

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    Prodigy 180 points

    In the datasheet Power Config is 

    and 

    Why does Power Config have two different default values in Technical reference Manual ?

  • 0 in reply to Alan Frias
    Prodigy 180 points

    Hello Alan,

    In the above Schematics we have DNP permanent pull down of ENAB. We have set the auto shutdown   time to 2 min. after 3 min both the FETs CHG and DSG has gone to OFF state but the fuel gauge is sourcing current from battery, about 150uA and 75uA and its toggling. Pulled the ENAB to gnd but its not enabling the CHG and DSG FETs. ?

  • 0 in reply to Alan Frias
    Prodigy 180 points

    Hello Alan,

     Could you please help us on this issue ?

    We are infact using TI  Fuel Gauge and TI Li-PO  Battery charger and planning to go for production. But we couldn't fix this fuel gauge issue. 

    Searched across TI forums and found that no exact solution is provided by TI on how to bring the Fuel gauge from Shutdown mode to Normal Mode.

    https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1330370/bq27z746-shutdown-mode-questions

    There are lots of Questions not answered by TI.

    1- The fuel gauge wakes from shutdown mode when its Pack terminal >VStartup- What is this Vstartup ? why there is no answer related to Vstartup, without knowing this how can we fix this issue ?.What is the Value of VStartup. 

    2-TI is saying this Fuel Gauge wakes from Shutdown when ENAB is pulled to LOW, that is not happening ? 

    3-After time based shutdown current drawn from the battery is toggling from 190uA to 70uA  what is the reason for this behavior ? 

    4-In forum its mention that the fuel Gauge does not go to shutdown if ENAB  pulled permanently LOW, But the CHG and DSG FETs  are off ,also its saying that when shutdown mode is activated I2C cannot be accessed, We could access the Fuel gauge data registers by connecting it to BQ Studio so is it really in shutdown Mode.

    Kindly support us on this issues, We are still not able to ship the devices to our customer since this is not solved.

    Thanks,

    Sobin.

  • 0 in reply to Sobin Sebastian
    TI__Mastermind 26135 points

    Hello Sobin,

    Sorry for the late response, I have received your questions and will work with the team to get a response sometime this week or early next week.

    Thank you,
    Alan

  • 0 in reply to Sobin Sebastian
    TI__Mastermind 24931 points

    Hello Sobin, 

    Vstartup is 2.0V typical for this gauge. In essence this requirement means that if there is a charger present then the gauge will wake up from shutdown mode. 

    How are you measuring the gauge iq? To obtain the gauge iq you must only provide power to the gauge through VDD and VSS, then you must take the average current consumed over at least a 30 second period. I have tested the gauge iq in shutdown mode for this gauge using the EVM and have measured an average iq consistent with the typical value we have spec'd in the device datasheet for shutdown mode. 

    If you can communicate with the gauge, then it is not in shutdown mode. You are also correct, if ENAB is permanently pulled low then it is impossible for the gauge to enter shutdown mode. I recommend referring to the enter and exit conditions for shutdown mode listed in the device Technical Reference Manual. 

    Regards, 

    Jonny. 

  • 0 in reply to Jonny
    Prodigy 180 points

    Hello Jonny,

    Thanku for your response.

    The takeaway from your response is Vstartup is 2.0V typical for this gauge. But even if we connect a charger/pull the Enab low this gauge is not going into Normal mode. If the device is disabling CHG and DSG FETS after  Auto shutdown time, what mode is it in ? It will enable its CHG and DSG FETs once the battery is removed and re-insert it.

    Referring to the Technical Reference Manual

    We are doing this, But not exiting from the UNKNOWN mode gauge is in, but current through FG is 190uA when in MAX.

    You are saying we cannot access gauge using I2C, so please confirm it will automatically get disconnected from BQSTUDIO ?

    We measured the Iq using an ammeter in series for more than 1 minute.. Min current is not less than 70uA, we are certain about it because battery voltage falls to Zero  in Weeks from full even when there is no load.

    Does TI have any Checklist or something for the USER to configure their Gauge with different battery's, for ex the if default capacity is 3000mAH, when we change it to 1000mAH what all parameters are to be changed.

    Please provide support on this along with previous queries.

    Adding to the above query, Have a doubt. I have been using a Battery with internal BMS, will that affect the fuel gauge. Or this fuel gauge is meant be used with a Battery (Li-po) without any BMS ? 

    Thanks,

    Sobin

     

  • 0 in reply to Sobin Sebastian
    TI__Mastermind 26135 points

    Hello Sobin,

    We are currently reviewing this question and will response when possible.

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    TI__Mastermind 26135 points

    Hello Sobin,

    Sobin Sebastian said:
    ut even if we connect a charger/pull the Enab low this gauge is not going into Normal mode

    This is dependent how much current you are pushing along with how you set your normal mode parameters, I would recommend looking into the exit condition parameters 

    Sobin Sebastian said:
    If the device is disabling CHG and DSG FETS after  Auto shutdown time, what mode is it in ? It will enable its CHG and DSG FETs once the battery is removed and re-insert it.

    FET will be enable/closed when there is current movement across the sense resistor

    Sobin Sebastian said:
    You are saying we cannot access gauge using I2C, so please confirm it will automatically get disconnected from BQSTUDIO ?

    -If you are using BqStudio that means there is communication going on meaning that it won't go into shutdown mode since the condition isn't meant. You can always access the gauge using I2C but it will cause a condition to exit it from shutdown/sleep/ship and etc. 

    Sobin Sebastian said:
    Does TI have any Checklist or something for the USER to configure their Gauge with different battery's, for ex the if default capacity is 3000mAH, when we change it to 1000mAH what all parameters are to be changed.

    -Please reference the EVM and the datasheet.

    EVM:https://www.ti.com/lit/ug/sluuch4a/sluuch4a.pdf?ts=1746564811184&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FBQ27Z746EVM-047
    Datasheet:https://www.ti.com/lit/ds/symlink/bq27z746.pdf?ts=1746564820564&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ27Z746

    Sobin Sebastian said:

    Please provide support on this along with previous queries.

    -Can you simplify the pervious queries in a bullet point list to better understand what question you still have remaining and to better provide a solution

    Sobin Sebastian said:
    Or this fuel gauge is meant be used with a Battery (Li-po) without any BMS ? 

    -It is meant to be without any BMS but adding another BMS can be added but it will export the same information as the gauge. The battery gauge is essentially a battery monitor but it contains the software to better calculate the state of charge of the cell.

    Thank you,
    Alan