INA228 datasheet(16/48 Pages) TI

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Settings for the conversion time and number of conversions averaged impact the effective measurement

resolution. For more detailed information on how averaging reduces noise and increases the effective number of

bits (ENOB) see Section 8.1.3.

7.3.5 Shunt Resistor Drift Compensation

The INA228 device has an internal temperature sensor which can measure die temperature from –40 °C to +125

°C. The accuracy of the temperature sensor is ±2 °C across the operational temperature range. The temperature

value is stored inside the DIETEMP register and can be read through the digital interface.

The device has the capability to utilize the temperature measurement to compensate for shunt resistor

temperature variance. This feature can be enabled by setting the TEMPCOMP bit in the CONFIG register, while

the SHUNT_TEMPCO is the register that can be programmed to enter the temperature coefficient of the used

shunt. The full scale value of the SHUNT_TEMPCO register is 16384 ppm/°C. The temperature compensation is

referenced to +25 °C . The shunt is always assumed to have a positive temperature coefficient and the

temperature compensation follows Equation 1:

RADJ = RNOM +

RNOM x (DIETEMP - 25) x SHUNT_TEMPCO

(1)

where

• RNOM is the nominal shunt resistance in Ohms at 25 °C.

• DIETEMP is the temperature value in the DIETEMP register in °C.

• SHUNT_TEMPCO is the shunt temperature coefficient in ppm/°C.

When this feature is enabled and correctly programmed, the CURRENT register data is corrected by constantly

monitoring the die temperature and becomes a function of temperature. The effectiveness of the compensation

will depend on how well the resistor and the INA228 are thermally coupled since the die temperature of the

INA228 is used for the compensation.

Note

Warning: If temperature compensation is enabled under some conditions, the calculated current

result may be lower than the actual value. This condition typically occurs when there is a high value of

shunt voltage ( >70% of full range), there is a shunt with high temperature-coefficient value ( >2000

ppm/°C), and there is a high temperature ( >100°C). Consider the example of constant current flowing

through a high temperature coefficient shunt such that at lower temperatures the shunt voltage is in its

upper range. As the temperature increases, the device will correctly report a constant current until the

maximum shunt voltage is reached. As temperature continues to increase after the maximum shunt

voltage is reached, the device will start reporting lower currents. This is because the effective

resistance calculated will continue to increase while the detected shunt voltage will remain constant

due to the voltage exceeding the selected ADC range.

7.3.6 Integrated Precision Oscillator

The internal timebase of the device is provided by an internal oscillator that is trimmed to less than 0.5%

tolerance at room temperature. The precision oscillator is the timing source for ADC conversions, as well as the

time-count used for calculation of energy and charge. The digital filter response varies with conversion time;

therefore, the precise clock ensures filter response and notch frequency consistency across temperature. On

power up, the internal oscillator and ADC take roughly 300 µs to reach <1% error stability. Once the clock

stabilizes, the ADC data output will be accurate to the electrical specifications provided in Section 6.

7.3.7 Multi-Alert Monitoring and Fault Detection

The INA228 includes a multipurpose, open-drain ALERT output pin that can be used to report multiple

diagnostics or as an indicator that the ADC conversion is complete when the device is operating in both triggered

and continuous conversion mode. The diagnostics listed in Table 7-1 are constantly monitored and can be

INA228

SLYS021 – JANUARY 2021

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