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BQ34Z100-R2: Circuit component calculations

Randy Draper
Prodigy 30 points
Part Number: BQ34Z100-R2

I am using a Neewer 7.4V, 5600mAh, 41.4 Watt Hour lithium ion battery professional camera battery to power our design.

.I am using Figure 8-3 on page 13 of the BQ34Z100-R2 PDF  datasheet as a reference guide for this battery but I am running into some design problems.

I am look at the Detailed Design Procedure on page 15 of this document but I do not understand the calculations in Step 1, Step 3, and Step 4.

Would it be possible for you to clarify this calculations or show me the calculations based on the Neerwer battery information I gave you.

Thank you.

Randy Draper

WidePath Communnications Inc.

  • 0
    TI__Genius 12215 points

        Step1 is regarding how to configure the Design Capacity, Design Energy and Cell Charge Voltage in the data flash, say if the capacity of the battery is 5600mAh, for such capacity and application for camera, current do not needs to be scaled down to be accommodated by the 2 bytes side Design Capacity parameter in dataflash, you can set Current Scale to 1, which will consequently be the value reported by CurrScale() command. And set the Design Capacity in dataflash as 5600mAh. The Energy Scale in dataflash can also be set as the default value of 1, then the value stored in Design Energy should be 4144 cWH.

       The Cell Charge Voltage is the charging voltage averaged to single cell, no scale needs to be considered, just use desired value specified in the Cell spec under different temperature should be fine, or you can consult the cell vendor if some of the charging voltages are not specified in the spec.

       For Step 3, it is regarding how to calculate the top and bottom legs of the voltage divider resistor string, which are R1 and R7 in figure 8-3, the formula is to scaled down the maximum battery voltage to around 0.9v at BAT pin for gauge ADC input

        For Step 4 is regarding how to determine the value of sense resistor, if the maximum absolute value of current is 10A, the a 10mOhm resistor can be considered, so that 10*10=100mV can be within the +/-125mV for most optimum current input range, +/-300mV is only for max sustainable input range, but the current can be measured correctly when it is out of +/-125mV range.