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8.5 Programming

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. 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

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. RSHUNT 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.

CAL =

0.00512

Current_LSB

SHUNT

(1)

Maximum Expected Current

Current_LSB =

(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

8.5.1 Programming the Calibration Register

Figure 9-1 shows a nominal 10-A load that creates a differential voltage of 20 mV across a 2-mΩ shunt resistor.

The bus voltage for the INA230 is measured at the external VBUS input pin, which in this example is connected

to the IN– pin to measure the voltage level delivered to the load. For this example, the VBUS pin measures less

than 12 V because the voltage at the IN– pin is 11.98 V as a result of the voltage drop across the shunt resistor.

For this example, assuming a maximum expected current of 15 A, the Current_LSB is calculated to be 457.7

μA/bit using Equation 2. Using a value for the Current_LSB of 500 μA/bit or 1 mA/bit would significantly simplify

the conversion from the Current register (04h) and Power register (03h) to amperes and watts. For this example,

a value of 1 mA/bit was chosen for the Current_LSB. Using this value for the Current_LSB does trade a small

amount of resolution for having a simpler conversion process on the user side. Using Equation 1 in this example

with a Current_LSB value of 1 mA/bit and a shunt resistor of 2 mΩ results in a Calibration register value of 2560,

or A00h.

The Current register (04h) is then calculated by multiplying the decimal value of the Shunt Voltage register (01h)

contents by the decimal value of the Calibration register and then dividing by 2048, as shown in Equation 3.

For this example, the Shunt Voltage register contains a value of 8,000 (representing 20 mV), which is multiplied

by the Calibration register value of 2560 and then divided by 2048 to yield a decimal value for the Current

example.

ShuntVoltage

CalibrationRegister

2048

Current =

(3)

INA230

SBOS601A – FEBRUARY 2012 – REVISED DECEMBER 2021

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