• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 2 answers
  • Subscribers 65 subscribers
  • Views 618 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ76940: Please help me check the schematic, concerning bq76940

user5811580
Intellectual 700 points
Part Number: BQ76940
Other Parts Discussed in Thread: BQ78350, BQ76200

The schematic of BQ76940 is listed as below.

Would you please help me have a look and have a check?

Thanks a lot.

  • 0
    Intellectual 700 points
    I want to make a BMS made up of BQ76940+BQ78350+BQ76200,which would support 12 batteries.
  • 0 in reply to user5811580
    TI__Guru* 80963 points
    Hi Wu,

    I've looked over these images, and I do not see any major issues. There are some parts of the schematic that are not included. For example, the sense resistor and the charge/discharge FETs are not showing.
    I will also ask my colleague to take a look at this to make sure there is nothing I am missing.

    Best regards,
    Matt
  • 0 in reply to user5811580
    TI__Guru 54715 points
    Hi Wu,
    The bottom of C19 should connect to the gnd reference for VSS rather than VC0. See diagram 8-3 in the data sheet.
    The 1 uF input caps at VCn pins are good but can show voltage effects when balancing due to filter settling times. Some designs use 0.22 uF or 0.1 uF, select something suitable for your system.
    REGOUT shows 0.1uF C27, the minimum recommended is 1 uF, 4.7 uF is typical if using the supply for external uses.
    With 12 cells you have 4 cells per group, if you are using CHG and DSG to drive FETs you may want to put the REGSRC limiting diode in the Q14 drain path rather than source for higher voltage. See the REGSRC Supply section of www.ti.com/lit/slua749.
  • 0 in reply to WM5295
    Intellectual 700 points
    Hi,WM5295.
    I have made changes according to your suggestions.
    I just got the PCB.
    Now , I met a question when bq76940 is powered up.
    The voltage of Cell1~Cell12 is normal at the beginning, which is almost 4.2V.
    However, the voltage of Cell 10 will be up to 5.6V, the voltage of Cell 11 will drop to 1.1V and the voltage of Cell 12 is also up to 5.6V after several seconds.

    Would you please give some suggestions?
  • 0 in reply to user5811580
    Intellectual 700 points
    in fact,the voltages of cells are normal.But,the voltage at VC15，VC13，VC12 is wrong.
  • 0 in reply to user5811580
    TI__Guru 54715 points
    Hi Wu,
    The voltage of cell 10 going up and cell 11 dropping to low voltage typically indicates the connection common to those cells is missing. Check that the wire is attached to the source (cell) and that R67 and the VC12 pin are soldered properly and free of contamination.
    If VC15, VC13 and VC12 associated cells are reading wrong, check that power is applied to BAT pin through its components. Check the voltage across the input resistor, it should be small. If it is sizable find the cause.