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BQ40Z50EVM-561: Configuring the BMS

Part Number: BQ40Z50EVM-561
Other Parts Discussed in Thread: BQ40Z50


We want to use the BQ40Z50 for our application with following parameters and functions.

1. 60Ah capacity battery pack - 96cells, 2.5Ah, 3.22V, 24 cells connected parallel and 4 such in series. -- Can we scale the pack current and Ah in the BQ40Z50 and also the shunt?

2. BMS should be able to estimate the SOC, SOH and have all the protections, it should be able to drive the charge and discharge FETs (30A continuous current)  -- How many FETs can the BQ40Z50 can drive?

3. Battery charger is a dumb charger and no interface available. So cannot take the commands from the BMS. But charger is having the fixed CC limits and CV limits -- Can we use the BQ40Z50 in non communication mode and charge / discharge the battery?.

4. BMS should be able to interface with host laptop as and when connected via the SMBus. This is only to see the status of the battery (will be used very rarely).


  • Hello Venkata,

    1. Yes, you are able to scale the pack current, Ah, and the sense resistor. Note that the EVM uses a 1 mOhm sense
    resistor and that you should not use a resistance less than this. You can do scaling by calibrating the gauge.
    2. The BQ40Z50 can drive 3 FETS: charge FET, discharge FET, and pre-charge FET.
    3. Yes, you do not need to have coordination between the charger and the gauge. As long as the gauge is enabled and the
    protection are enabled then everything should work just fine.
    4. Yes, you will be able to interface the gauge with a laptop. All you will need is an EV 2400 and to have BQStudios
    installed on your laptop.

    Nick Richards

  • Hai Nick,

    How to configure the BQ40Z50 to work in normal mode i.e enable it to work in discharge mode and automatically get charged when the charger is connected, without any intervention from user. Does the BQ40Z50 automatically controls the charge and discharge FETs to work in charge or discharge mode.

    I think before using the BQ40Z50 in normal operation, we should complete the learning cycle of the battery. How to initiate the learning cycle and how to know whether the learning cycle is successfully completed.


  • Hello Venkata,

    The BQ40Z50 will automatically be in Normal Mode when the battery is discharging or charging. You can read section
    5.1 of the Technical Reference Manual (TRM) to learn more about each mode that the gauge supports, and the parameters
    that dictate what mode the gauge will be in.

    Yes, when you enable the Charge and Discharge FETs, they will automatically control the corresponding FETs.

    It is highly recommended that you complete a learning cycle for your battery. To learn more about the learning cycle
    please reference this document: 

    Nick Richards