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WEBENCH® Tools/BQ24773: How to avoid battery over discharging in BQ24773

Rahul Surawase48
Expert 2395 points
Part Number: BQ24773
Other Parts Discussed in Thread: TPS61088

Tool/software: WEBENCH® Design Tools

Hello TI, 


              We are working on our Own BMS design system which have BQ24773, BQ27542 and TPS61088.

We looking to avoid battery leakage when it is not in use .

When the system Operated  in battery power state with load and battery is goes below to the minimum system voltage, therefor load is need to disconnect from BMS(Power source), but the BMS steel ON and it's drain the battery till reach at depleted, we want to shutdown the BMS when battery voltage goes below the Minimum system voltage.

There is any Disable option in BQ24773 to avoid Over discharging the battery pack ..?

There is any Identification parameter in BQ24773 register command set for Battery charging and discharging Done notification to host controller ..?

What is suitable option to implement above mention feature in our BMS ..?  

In our System we don't have required number of ADC to read the BQ24773 parameter like IADP, IBAT and PMON, we are looking for the I2C based ADC IC please suggest us suitable part to our design, currently we are selected ADC128D818CIMTX  

Thanks and regards,

Rahul Surawase 

  • 0
    TI__Mastermind 25800 points

    Hey Rahul,

    There is no function to remove the discharge path between the battery and the system. Because of the BATFET body diode, the battery always has a path to the system and its load.

    You can potentially add some circuit between your system load the charger system rail like a load switch and disable it whenever the battery voltage falls below a certain level. The BQ24773 has an integrated independent comparator that you may use to monitor the battery voltage and trigger to disable the load switch with.

    There is no battery charging/discharging notification on this charger. Charging done is handled entirely by the host controller. 

    As mentioned above, I would suggest a load switch circuit that is controlled by the independent comparator of the charger.

    I do not have a recommendation for an ADC. I would suggest posting a new thread to the analog forum looking for a I2C based ADC.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Expert 2395 points

    Hello Joel, 


                      There is no function to remove the discharge path between the battery and the system. Because of the BATFET body diode, the battery always has a path to the system and its load. what is the use case of  BATFET, if it's not going to shut-down the battery Discharging ..?

    you mean, BATFET not going to turn of ever ..? we observe that, when we sent send FORCE BATFET Off (1: Turn off BATFET) load still ON but it's robot because of insufficient Power, is it expected result..?

    We need to full turn of the BATFET, to avoid leakage discharge current when BATFET is OFF, you have any suggestion on it ..?

    We expecting when BATFET get this instruction FORCE BATFET Off (1: Turn off BATFET) BATFET going to OFF state and load is disconnected from the system, is it possible...? if NO, provide reliable alternative to it ....

    I would suggest a load switch circuit that is controlled by the independent comparator of the charger. Can you please suggest suitable part for our System , we not aware about the load switch 

    There is no function to remove the discharge path between the battery and the system. Because of the BATFET body diode, the battery always has a path to the system and its load.  there is any alternative MOSFET to avoid battery path to load.

    find the attachment for schematic design, please refer the design schematic for more details.BMS_Schematic.pdf

    Thanks and regard, 

    Rahul Surawase 

  • 0 in reply to Rahul Surawase48
    TI__Mastermind 25800 points

    Hey Rahul,

    Rahul Surawase48 said:
    what is the use case of  BATFET, if it's not going to shut-down the battery Discharging ..?

    The BATFET is there to allow a path to power the system from either the buck converter or the battery. If the adapter is not present and the buck converter is not operating, the battery can support the system load. 

    Rahul Surawase48 said:
    you mean, BATFET not going to turn of ever ..? we observe that, when we sent send FORCE BATFET Off (1: Turn off BATFET) load still ON but it's robot because of insufficient Power, is it expected result..?

    If you turn off the BATFET, you will see a body diode effect to your system, meaning the system voltage will be VBAT - Vf,BATFET, typically ~1V for the parasitic body diode. This behavior may cause a brownout if your system cannot operate at VBAT - Vf,BATFET. 

    Rahul Surawase48 said:
    We need to full turn of the BATFET, to avoid leakage discharge current when BATFET is OFF, you have any suggestion on it ..?

    I would actually suggest adding a load switch between your system rail and the system load. This would give you a full disconnect in either scenario (battery only or adapter + battery).

    Rahul Surawase48 said:
    We expecting when BATFET get this instruction FORCE BATFET Off (1: Turn off BATFET) BATFET going to OFF state and load is disconnected from the system, is it possible...? if NO, provide reliable alternative to it ....

    Again, force BATFET does stops driving the BATFET (this reduces on-chip consumption for the BATFET gate driver). 

    Rahul Surawase48 said:
    Can you please suggest suitable part for our System , we not aware about the load switch 

    For the load switches, you can find our product selection here: http://www.ti.com/power-management/power-switches/load-switches/products.html. I would identify products within your battery and system voltage range as well as rated up to your peak load current. All you really need is an enable switch to control the disconnect event. 

    Rahul Surawase48 said:
    there is any alternative MOSFET to avoid battery path to load.

    There are no alternative MOSFETs for this situation. All MOSFETs have an inherent parasitic diode due to the construction of MOSFETs. 

    Regards,

    Joel H