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BQ76952: Resistive cell simulator

Francis Jiang
Intellectual 1650 points
Part Number: BQ76952

Hi Team,

On the BQ76952 EVM, there is a resistive cell simulator made up of 200-Ω series resistors (BQ76952EVM User's Guide (Rev. A) Fig. 5-10).

Can this 200 ohm resistors be replaced with 10k or 100k ohm resistors? In actual tests, the 10k and 100k ohm resistors will effect the voltage measurement. So, what is the range of series resistors? How them effect the internal voltage measurement?  

Best Regards

Francis Jiang

  • 0
    TI__Expert 8496 points

    Hi Francis,

    We recommend using the 200 ohm resistance value shown in the EVM documentation because the part sinks a small amount of current while taking voltage measurements.  If you use resistor values that are too large in the cell balancing resistor divider, then voltage drop will be too high, resulting in incorrect voltage measurements.  As you increase the resistance values in the resistor divider, the voltage measurements you collect will gradually become more inaccurate.  For best accuracy, we recommend using 200 ohm resistors.

    Best,

    Andria

  • 0 in reply to Andria McIntyre
    TI__Intellectual 1650 points

    Hi Andria,

    According to your comment, what is the direction of current flow and what is the principle of voltage measurement? (I understand there is an op amp.)

    Andria McIntyre said:
    because the part sinks a small amount of current while taking voltage measurements.

    Could you please explain in more detail what voltage will drop?

    Andria McIntyre said:
    then voltage drop will be too high

    Best Regards

    Francis Jiang

  • +1 in reply to Francis Jiang
    TI__Expert 8496 points

    Hi Francis,

    In response to your questions:

    Francis Jiang said:
    what is the direction of current flow and what is the principle of voltage measurement?

    Sinking current means that current is flowing into the BQ76952.  To learn more about voltage measurement in the BQ76952, please refer to Section 4.1 Voltage Measurement in the TRM (BQ76952 Technical Reference Manual (Rev. B) (ti.com)).

    Francis Jiang said:
    Could you please explain in more detail what voltage will drop?

    There will be measurement error during sampling when voltage drops across the cell simulator resistor divider network.  The mechanism for current flow and voltage drop is very complex, and attempting to explain it here is not feasible.  Essentially, increasing the resistor values in the cell simulator network will lead to an undesirably high voltage drop across the top cell simulator resistor and a higher current going into the BQ76952.  The effects of this are complicated, but ultimately lead to inaccurate voltage readings.

    Best,

    Andria

  • +1 in reply to Andria McIntyre
    TI__Intellectual 1650 points

    Hi Andria,

    Thanks for your detailed comments. I think I roughly understand the role of the sinking current.

    Best Regards,

    Francis Jiang