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Original question:

BQ76940: BQ76940

BQ76940: Power management forum

Jitendra Parit
Prodigy 90 points
Part Number: BQ76940
Other Parts Discussed in Thread: TIDA-010030, TIDA-00792, CSD19536KTT

Hii..This is Jitendra 

respected sir

I want to design  BMS 48v and 100A rating

using BQ76940 ic 

sir, I want to ask only schematics which is given in design reference will be enough or we need to change anything in given schematics 

sir, please reply because I am just beginner in this

  • 0
    TI__Genius 10830 points

    Hi Jitendra,
    Please find here a few reference designs which you can reuse for your 48V project.

  • 0 in reply to David Hien
    Prodigy 90 points

    Respacted sir

    I have been reading   reference design of BQ76940

    but I am worry about current rating of bq76940 design bms

    if my rating is 48VOLT and  100A and 48volt ,60A in both case 

    Do I follow the same schematics which is given in BQ76940 reference design  or i need to change anything .

    If I need to change external protection Internal protection FET protection or any capacitor , resistance then which basis I should change the value and component rating

    please reply me while considering as a beginner

  • 0 in reply to Jitendra Parit
    TI__Guru 54715 points

    Hi Jitendra,

    You may need to modify the reference designs for your system environment.  If your specifications require more current than the reference designs you will most likely need to modify the reference designs.  Check the basic function of the designs, these may match what you need well, or you may select features from each.

    For example, the TIDA-00792 design guide shows at 30A and the sense resistors heating in figure 25.  When you increase the current by 2X you will increase the power by 4X and it will get hotter.  The FETs will be similar.  While the CSD19536KTT shown in the reference design can carry 100A, its use will likely be limited by how well you can get heat away from the part in the design.  TIDA-010030 uses 3 FETs in parallel, but again check the thermal conditions available for your design.

    In general, after you consider your features:

    • Look at the current dynamic range of your system.  Plan the sense resistor for the short circuit capability and the gauging measurement range of the monitors.  If you need short circuit at 100A, remember there is some tolerance and select a sense resistor which will let you achieve the level with the available selections.  Consider also your gauging currents.  If you need to gauge 100A without trip, keep the voltage in the proper sense input range.  Consider also the minimum current you will need to gauge.  The part has a limited dynamic range, so sometimes there is a compromise.  If you are gauging high load current the small current resolution may be poor.
    • Consider the power requirements for the load current and the selected sense resistance.  Determine how to handle that power in your battery, and how many resistors might be used in parallel.
    • Consider the power in the FETs selected.  You may need to have multiple FETs and consider how much heat you can get out of the battery.

    It can be complex to design a system.  I hope these are helpful.