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BQ76930: Inquiry about temperature calculation method using bq76940 evaluation software

kim myoungsoo
Prodigy 65 points
Part Number: BQ76930
Other Parts Discussed in Thread: BQ76940,

Hi

I have a question about converting the temperature data to the actual temperature when checking the data using i2c communication with the bq76930 chip using the bq76940 evaluation software.

Please tell me how to derive the data “0x1085 Vtsx” displayed on Temp Sensor 2 in the current window among the attached picture files as the actual temperature using a calculation formula.

"VTSX = (ADC in Decimal) x 382 µV/LSB (4)

 RTS = (10,000 × VTSX) ÷ (3.3 – VTSX)"

If you look at the menu, it says to use the above formula, but I don't know how to calculate it in detail.

NOTE: The thermistor resistor value is 10K Ohm

Please...

 

  • +1
    TI__Guru 54715 points

    Hi Kim,

    In the picture shown the Stack V/T/I section is selected to display raw counts, so the ADC result is displayed without processing.  0x1085 is the ADC value in hex.  In decimal 4229.

    To get the VTSx us the formula, here VTS2 = 4229 LSB x 382 uV/LSB = 1615478 uV or 1.615 V

    The RTS formula is from the voltage divider with the internal 3.3V and 10k resistance, VTS = 3.3V x RTS/(RTS+10,000).  Solving for RTS gives the equation shown.

    RTS = (10000 x 1.615)/(3.3 - 1.615) = 9585 ohms.

    Looking up 9585 in your thermistor data sheet will give you a temperature.  For the 103AT-2 thermistor on the EVM this corresponds to between 25 and 30 deg C.  You can interpolate or use an equation or a look up table as desired to derive a temperature.