INA3221 datasheet(18/50 Pages) TI2

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7.4.2.2 Averaging and Conversion-Time Considerations

The INA3221 has programmable conversion times for both the shunt- and bus-voltage measurements. The

selectable conversion times for these measurements range from 140μs to 8.244ms. The conversion-time

settings, along with the programmable-averaging mode, enable the INA3221 to optimize available timing

requirements in a given application. For example, if a system requires data to be read every 2ms with all

three channels monitored, configure the INA3221 with the conversion times for the shunt- and bus-voltage

measurements set to 332μs.

The INA3221 can also be configured with a different conversion-time setting for the shunt- and bus-voltage

measurements. This approach is common in applications where the bus voltage tends to be relatively stable,

and allows for the time focused on the bus voltage measurement to be reduced relative to the shunt-voltage

measurement. For example, the shunt-voltage conversion time can be set to 4.156ms with the bus-voltage

conversion time set to 588μs for a 5ms update time.

There are trade-offs associated with the conversion-time and averaging-mode settings. The averaging feature

significantly improves the measurement accuracy by effectively filtering the signal. This approach allows the

INA3221 to reduce the amount of noise in the measurement caused by noise coupling into the signal. A greater

number of averages allows the INA3221 to be more effective in reducing the measurement noise component.

The trade-off to this noise reduction is that the averaged value has a longer response time to input-signal

changes. This aspect of the averaging feature is mitigated to some extent with the critical-alert feature that

compares each single conversion to determine if a measured signal (with noise component) has exceeded the

maximum acceptable level.

The selected conversion times also have an impact on measurement accuracy. This effect can seen in

Figure 7-7. The multiple conversion times shown in Figure 7-7 illustrate the impact of noise on measurement.

These curves shown do not use averaging. to achieve the highest-accuracy measurement possible, use a

combination of the longest allowable conversion times and highest number of averages, based on system timing

requirements.

−120

−80

−40

120

Conversion Time: 140µs

Conversion Time: 332µs

Conversion Time: 1.1ms

200

400

600

800

1000

Number of Conversions

Figure 7-7. Noise Versus Conversion Time

INA3221

SBOS576C – MAY 2012 – REVISED SEPTEMBER 2025

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