INA230 datasheet(17/44 Pages) TI

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The LSB for the Bus Voltage register (02h) is a fixed 1.25 mV/bit, which means that the 11.98 V present at the

VBUS pin results in a register value of 2570h, or a decimal equivalent of 9584. Note that the MSB of the Bus

Voltage register (02h) is always zero because the VBUS pin is only able to measure positive voltages.

The Power register (03h) is then calculated by multiplying the decimal value of the Current register, 10000, by

the decimal value of the Bus Voltage register (02h), 9584, and then dividing by 20,000, as defined in Equation

4. For this example, the result for the Power register (03h) is 12B8h, or a decimal equivalent of 4792. Multiplying

this result by the power LSB (25 times the [1 × 10–3 Current_LSB]) results in a power calculation of (4792

× 25 mW/bit), or 119.82 W. The power LSB has a fixed ratio to the Current_LSB of 25. For this example, a

programmed 1 mA/bit Current_LSB results in a power LSB of 25 mW/bit. This ratio is internally programmed

to ensure that the scaling of the power calculation is within an acceptable range. A manual calculation for the

power being delivered to the load would use a bus voltage of 11.98 V (12 VCM – 20 mV shunt drop) multiplied by

the load current of 10 A to give a result of 119.8 W.

Current

BusVoltage

20,000

Power =

(4)

Table 8-1 lists the steps for configuring, measuring, and calculating the values for current and power for this

device.

Table 8-1. Calculating Current and Power(1)

STEP

ADDRESS

CONTENTS

DEC

LSB

VALUE

Step 1

Configuration register

00h

4127h

—

Step 2

Shunt register

01h

1F40h

8000

2.5 µV

20 mV

Step 3

Bus Voltage register

02h

2570h

9584

1.25 mV

11.98 V

Step 4

Calibration register

05h

A00h

2560

—

Step 5

Current register

04h

2710

10000

1 mA

10 A

Step 6

Power register

03h

12B8h

4792

25 mW

119.82 W

(1)

Conditions: Load = 10 A, VCM = 12 V, RSHUNT = 2 mΩ, and VVBUS = 12 V.

8.5.2 Programming the INA230 Power Measurement Engine

8.5.2.1 Calibration Register and Scaling

The Calibration register makes it possible to set the scaling of the Current and Power registers to the values that

are most useful for a given application. One strategy may be to set the Calibration register so that the largest

possible number is generated in the Current register or Power register at the expected full-scale point. This

approach yields the highest resolution based on the previously calculated minimum Current_LSB in the equation

for the Calibration register (Equation 1). The Calibration register can also be selected to provide values in the

Current and Power registers that either provide direct decimal equivalents of the values being measured, or

yield a round LSB value for each corresponding register. After these choices have been made, the Calibration

an external ammeter, the exact current is known. The value of the Calibration register can then be adjusted

based on the measured current result of the INA230 to cancel the total system error, as shown in Equation 5.

Corrected_Full_Scale_Cal = trunc

Cal

MeasShuntCurrent

INA230_Current

(5)

8.5.3 Simple Current Shunt Monitor Usage (No Programming Necessary)

The INA230 can be used without any programming if it is only necessary to read a shunt voltage drop and bus

voltage with the default power-on reset configuration and continuous conversion of shunt and bus voltage.

Without programming the INA230 Calibration register, the device is unable to provide either a valid current or

power value, because these outputs are both derived using the values loaded into the Calibration register.

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INA230

SBOS601A – FEBRUARY 2012 – REVISED DECEMBER 2021

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