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BQ76930 OV and UV protections

Rania Chaibi
Intellectual 290 points

Hi,

To write OV_TRIP and UV_TRIP to the corresponding registers I read in the datasheet that I should calculate  OV_TRIP_FULL and  UV_TRIP_FUL as follows

 OV_TRIP_FULL = (OV – ADCOFFSET) ÷ ADCGAIN

UV_TRIP_FULL = (UV – ADCOFFSET) ÷ ADCGAIN

the value of adcoffset that i read is 0xCE  (206 in decimal), so shoud I use this value directly to calculate the OV and UV_TRIP_FULL? I had read in the datasheet (p 40) that there is 2 complement scale range .

  • 0
    TI__Expert 6085 points

    Section 7.3.1.2 in the D/S can be little confusing.

    please read the Design requirement section of selection of OV Trip.

     

    (1)     There is *only* a 14-bit ADC in the device for cell voltage measurement.

     

    (2)     When the cell( 2V-5V)is measured with a 14 bit  ADC, 1LSB = 5V/2^14 = 380uV.

     

    A 14-bit “register representation” is adequate for 0-16V. There are no concerns here.

     

    However, in the stack “pack” measurement up to 65V, a 16 bit-register representation(unassigned integer, also cannot be zero), is needed.

     

    So, to obtain it, the measured 14 bit ADC value, is shifted left by 2 bits to be represented in a 16-bit register format.

    This is the same as multiplying by 4. Hence the new LSB is, 380uV *4 = 1.520mV. 

     

    As an example, if the 14-bit ADC is  0x2C86. If shifted left by 2 bits, the new 16-bit representation would 0xB218.