INA230 Datasheet, PDF (15/35 Pages) Texas Instruments – High- or Low-Side Measurement

INA230
www.ti.com
SBOS601 – FEBRUARY 2012
PROGRAMMING THE INA230
An important aspect of the INA230 is that it does not necessarily measure current or power. The INA230
measures both the differential voltage applied between the IN+ and IN– input pins and the voltage applied to the
BUS pin. In order for the INA230 to report both current and power values, both the Current register resolution
and the value of the shunt resistor present in the application that resulted in the differential voltage being
developed must be programmed. The Power register is internally set to be 25 times the programmed least
significant bit of the current register (Current_LSB). Both the Current_LSB and shunt resistor value are used
when calculating the Calibration register value. The INA230 uses this value to calculate the corresponding
current and power values based on the measured shunt and bus voltages.
The Calibration register is calculated based on Equation 1. This equation includes the term Current_LSB, the
programmed value for the LSB for the Current register. This is the value used to convert the value in the Current
register to the actual current in amps. The highest resolution for the Current register can be obtained by using
the smallest allowable Current_LSB based on the maximum expected current, as shown in Equation 2. While this
value yields the highest resolution, it is common to select a value for the Current_LSB to the nearest round
number above this value to simplify the conversion of the Current register and Power register to amps and watts
respectively. R_SHUNT is the value of the external shunt used to develop the differential voltage across the input
pins. The 0.00512 value in Equation 1 is an internal fixed value used to ensure scaling is maintained properly.
0.00512
CAL = _{Current_LSB · RSHUNT}
(1)
Current_LSB
=
Maximum
Expected
2¹⁵
Current
(2)
After the Calibration register has been programmed, the Current register and Power register are updated
accordingly based on the corresponding shunt voltage and bus voltage measurements. Until the Calibration
register is programmed, the Current and Power registers remain at zero.
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