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BQ40Z50-R2: interconnect resistance value to enter

Daniel Yu
Prodigy 70 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50EVM-561

Hi there,

Use BQ40Z50EVM-561 as a cells connection target, Please help me decide the Cell 1..4 interconnect resistance value for entering  (please refer to the sluubk0a bq40Z50-R2 TRM page 230/267)

if the cells interconnect resistances are distributed as shown in the following circuit diagram:

Thanks a lot!

Daniel

  • 0
    TI__Mastermind 34665 points
    Hi Daniel,

    Interconnect resistance is the resistance between series cells connection to the high current path of the PACK PCB, not the filter resistance to the gauge. In your example above the interconnect resistances are
    Cell 1 : 10m
    Cell 2 : 10m
    Cell 3: 40m
    Cell 4: 0m
  • 0 in reply to Damian Lewis
    Prodigy 70 points
    Hi Damian,

    I am a little confused, according to the sluubk0a bq40Z50-R2 TRM page 230/267, it read as:
    Cell 1 Interconnect Resistance: This is the interconnect resistance value entered by the user that represents the interconnect
    resistance between the negative rail and the bottom of Cell 1(my take is R1=10m), plus the
    interconnect resistance of the connection from the bottom of the first cell to the gauge(my take is
    R1=10m).
    Cell 2 Interconnect Resistance: This is the interconnect resistance value entered by the user that represents the interconnect
    resistance between the top of Cell 1 and the bottom of the Cell 2(my take is R2+R3=20m), plus the
    interconnect resistance of the connection from the bottom of Cell 2 to the gauge(my take is
    R3+R4=110m).
    Cell 3 Interconnect Resistance: This is the interconnect resistance value entered by the user that represents the interconnect
    resistance between the top of Cell 2 and the bottom of the Cell 3(my take is R5+R6=20m), plus the
    interconnect resistance of the connection from the bottom of Cell 3 to the gauge(my take is
    R5+R6+R7=120m).
    Cell 4 Interconnect Resistance: This is the interconnect resistance value entered by the user that represents the interconnect
    resistance between the top of Cell 3 and the bottom of the Cell 4(my take is R8+R9=20m), plus the
    interconnect resistance of the connection from the bottom of Cell 4 to the gauge(my take is
    R10=100m).
    Could we re-phase the description in the TRM?

    If only interconnect resistances of the high current path should be considered as you mentioned above, then, should we change the cell interconnect resistances as follows:
    A). J1 1N and J2 1P which is associated to the voltage reading of cell1 will be R1+R2=20m (to be entered as cell 1 interconnect resistance)
    B). J2 1P and J3 2P which is associated to the voltage reading of cell2 will be R3=10m. (to be entered as cell 2 interconnect resistance)
    C). J3 2P and J4 3P which is associated to the voltage reading of cell3 will be R5+R6+R8+R9=40m. (to be entered as cell 3 interconnect resistance)
    D). J4 3P and J5 4P which is associated to the voltage reading of cell4 will be R11=10m. (to be entered as cell 4 interconnect resistance)

    Your guidance please.

    Thanks a lot!

    Daniel Yu
  • 0 in reply to Daniel Yu
    TI__Mastermind 34665 points
    Hi Daniel,

    The interconnect resistance are between the voltage sense nodes for each cell. It helps the gauge assess what the actual cell voltage is based on the current flowing, the interconnect resistance and the voltage measured. R4, R7 and R10 are not part of the interconnect resistance. They are going to the RC filter network for the gauge voltage sense measurements. Based on your drawing the cells interconnects are shown below, which aligns with A, B, C and D above. Sorry I misinterpreted your drawing above.

    Cell 1 : R1+ R2
    Cell 2 : R3
    Cell 3 : R5 + R6 + R8 + R9
    Cell 4 : R11