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Voltage supply for BQ2040

Charles Lambert
Prodigy 30 points
Other Parts Discussed in Thread: BQ2040

Hello,

My question is about BQ2040: http://www.ti.com/lit/ds/symlink/bq2040.pdf

Can I directly power the component using 28 NiMH cells and a 2N7002 FET, whereas the Chart 1 page 3 stops at 12 NiMH cells ?

If yes, what would be the ideal values for R4, R5, R11 ?

Thanks

  • 0 in reply to Charles Lambert
    TI__Intellectual 2120 points

    Hi Charles,

      For voltages that high an LDO is typically used to provide a solid Vcc.

    As for the values of R4 and R5, the formula is in the DS.

    Voltage Thresholds

    In conjunction with monitoring VSR for charge/discharge currents, the bq2040 monitors the battery potential

    through the SB pin. The voltage potential is determined through a resistor-divider network per the following

    equation:

    R5 / R4 = (MBV / 2.25) -1

    where MBV is the maximum battery voltage, R5 is connected to the positive battery terminal, and R4 is connected to the negative battery terminal. R5/R4 should be

    rounded to the next higher integer. The voltage at the SB pin (VSB) should never exceed 2.4V.

    Also, the total of R4 + R5 should be no more than ~1M

    Best regards

    Garry

  • 0 in reply to Garry Elder
    Prodigy 30 points

    thank you for the answer,

    I will use R4 = 34K, R5 = 909K, R11 = 3,3M and keep informed anyone following this post if it doesn't work as expected.