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BQ76952: Resistor Value Selection for REG Current Limiting (3S to 16S Setup)

Yasir Ziya Gültak
Prodigy 50 points
Part Number: BQ76952

Tool/software:

Hello,
Whether I use a 3S connection or a 16S connection, I would like to draw a total of 90mA current for REG1 and REG2.

 Let’s assume a 5S connection, with each cell at 3 V, and Vsat = 0.2 V. In that case,

current is obtained. Is my calculation correct? If so, what resistor value should I use?

  • 0
    TI__Prodigy 730 points

    Your equation seems correct for calculating the current limit for a BJT with Vce=0.2V, and REGIN=5.5V ,and Rseries=440
    For 16S configuration, the EVM typically uses 440ohm in series with the BJT's collector, and also a Diode to prevent reverse bias leakage from BREG to BAT.
    For a 3S configuration, assuming 3V per cell, the series resistor would need to be ~36ohm to maintain 90mA before the BJT would be current limited.

  • 0 in reply to Gavin Long
    Prodigy 50 points

    Thanks for the quick reply
    I need to choose the Rseries resistor with a low value in order to supply enough current for both the 3S and 16S connections. However, in this case, at high CD voltages, the transistor dissipates a lot of power. That’s why I decided to supply the REGIN pin externally. According to the datasheet, the circuit looks like the one in the figure. Do you think there is any mistake? 

  • +1 in reply to Yasir Ziya Gültak
    TI__Prodigy 730 points

    This is correct. If BREG pin is not used but REGIN pin is used (such as driven from an external source), then this pin should be connected to REGIN.