The RSHUNT term is the resistance value of the external shunt used to develop the differential voltage across the

IN+ and IN– pins. Use Equation 1 for ADCRANGE = 0. For ADCRANGE = 1, the value of SHUNT_CAL must be

divided by 4.

SHUNT_CAL =

0.00512

Current_LSB × RSHUNT

(1)

where

• 0.00512 is an internal fixed value used to ensure scaling is maintained properly.

• CURRENT_LSB is a selected value for the current step size in amperes. Must be greater than or equal to

CURRENT_LSB (minimum), but less than 8 x CURRENT_LSB(minimum) to reduce resolution loss.

• The value of SHUNT_CAL must be divided by 4 for ADCRANGE = 1.

(2)

Note that the current is calculated following a shunt voltage measurement based on the value set in the

SHUNT_CAL register. If the value loaded into the SHUNT_CAL register is zero, the current value reported

through the CURRENT register is also zero.

After programming the SHUNT_CAL register with the calculated value, the measured current in Amperes can be

read from the CURRENT register. Use Equation 3 to calculate the final value scaled by the CURRENT_LSB:

Current [A] = CURRENT_LSB x CURRENT

(3)

where

• CURRENT is the value read from the CURRENT register

The power value can be read from the POWER register as a 16-bit value. Use Equation 4 to convert the power

to Watts:

Power [W] = 32 x CURRENT_LSB x POWER

(4)

where

• POWER is the value read from the POWER register.

• CURRENT_LSB is selected value for the lsb size of the current calculation used in Equation 1.

Refer to Detailed Design Procedure for a design example using these equations.

8.1.3 ADC Output Data Rate and Noise Performance

The INA232 noise performance and effective resolution depend on the ADC conversion time. The device

also supports digital averaging which can further help decrease digital noise. The flexibility of the device to

select ADC conversion time and data averaging offers increased signal-to-noise ratio and achieves the highest

dynamic range with lowest offset. The profile of the noise at lower signals levels is dominated by the system

noise that is comprised mainly of 1/f noise or white noise. The effective resolution of the ADC can be increased

by increasing the conversion time and increasing the number of averages.

Table 8-2 summarizes the output data rate conversion settings supported by the device. The fastest conversion

setting is 140 µs. Typical noise-free resolution is represented as Effective Number of Bits (ENOB) based on

device measured data. The ENOB is calculated based on noise peak-to-peak values, which assures that full

noise distribution is taken into consideration.

INA232

SBOSAA2 – DECEMBER 2022

www.ti.com

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