INA237 datasheet(29/45 Pages) TI

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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

multiplied by 4.

SHUNT_CAL = 819.2 x 10

6 x CURRENT_LSB x R

SHUNT

(1)

where

• 819.2 x 106 is an internal fixed value used to ensure scaling is maintained properly.

• the value of SHUNT_CAL must be multiplied by 4 for ADCRANGE = 1.

Maximum Expected Current

Current_LSB =

(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. The final value is scaled by CURRENT_LSB and calculated in Equation 3:

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 24-bit value and converted to Watts by using

Equation 4:

Power [W] = 0.2 x CURRENT_LSB x POWER

(4)

where

• POWER is the value read from the POWER register.

• CURRENT_LSB is the lsb size of the current calculation as defined by Equation 2.

For a design example using these equations refer to Section 8.2.2.

8.1.3 ADC Output Data Rate and Noise Performance

The INA237 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 INA237 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 50 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.

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INA237

SBOSA20 – FEBRUARY 2021

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