SLYS021A January 2021 – May 2022 INA228
Parametric values are calculated by multiplying the returned value by the LSB value. Table 8-4 below shows the returned values for this application example assuming the design requirements shown in Table 8-3.
|PARAMETER||Returned Value||LSB Value||Calculated Value|
|Shunt voltage (V)||311040d||312.5 nV/LSB||0.0972 V|
|Current (A)||314572d||10 A/ 219 = 19.073486 µA/LSB||6 A|
|Bus voltage (V)||245760d||195.3125 µV/LSB||48 V|
|Power (W)||4718604d||Current LSB x 3.2 = 61.035156 µW/LSB||288 W|
|Energy (J)||1061683200d||Power LSB x 16 = 976.5625 µJ/LSB||1036800 J|
|Charge (C)||1132462080d||Current LSB = 19.073486 µC/LSB||21600 C|
|Temperature (°C)||3200d||7.8125 m°C/LSB||25°C|
Shunt Voltage, Current, Bus Voltage (positive only), Charge, and Temperature return values in two's complement format. In two's complement format a negative value in binary is represented by having a 1 in the most significant bit of the returned value. These values can be converted to decimal by first inverting all the bits and adding 1 to obtain the unsigned binary value. This value should then be converted to decimal with the negative sign applied. For example, assume a shunt voltage reading returns 1011 0100 0001 0000 0000. This is a negative value due to the MSB having a value of one. Inverting the bits and adding one results in 0100 1011 1111 0000 0000 (311040d) which from the shunt voltage example in Table 8-4 correlates to a voltage of 97.2 mV. Since the returned value was negative the measured shunt voltage value is -97.2 mV.