measured shunt voltage to determine if the measurements has exceeded the programmed limit. The AFF, bit

4 of the Mask/Enable Register, asserts high any time the measured voltage exceeds the value programmed

into the Alert Limit Register. In addition to the AFF being asserted, the Alert pin is asserted based on the Alert

Polarity Bit (APOL, bit 1 of the Mask/Enable Register). If the Alert Latch is enabled, the AFF and Alert pin remain

asserted until either the Configuration Register (00h) is written to or the Mask/Enable Register is read.

The Bus Voltage alert functions compare the measured bus voltage to the Alert Limit Register following every

bus voltage conversion and assert the AFF bit and Alert pin if the limit threshold is exceeded.

The Power Over-Limit alert function is also compared to the calculated power value following every bus voltage

measurement conversion and asserts the AFF bit and Alert pin if the limit threshold is exceeded.

6.4 Device Functional Modes

6.4.1 Averaging and Conversion Time Considerations

The INA226 device offers programmable conversion times (tCT) for both the shunt voltage and bus voltage

measurements. The conversion times for these measurements can be selected from as fast as 140 μs to as long

as 8.244 ms. The conversion time settings, along with the programmable averaging mode, allow the device to be

configured to optimize the available timing requirements in a given application. For example, if a system requires

that data be read every 5ms, the device can be configured with the conversion times set to 588 μs for both shunt

and bus voltage measurements and the averaging mode set to 4. This configuration results in the data updating

approximately every 4.7ms. The device can also be configured with a different conversion time setting for the

shunt and bus voltage measurements. This type of approach is common in applications where the bus voltage

tends to be relatively stable. This situation can allow for the time focused on the bus voltage measurement to

be reduced relative to the shunt voltage measurement. The shunt voltage conversion time can be set to 4.156

ms with the bus voltage conversion time set to 588 μs, with the averaging mode set to 1. This configuration also

results in data updating approximately every 4.7 ms.

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

averaging feature can significantly improve the measurement accuracy by effectively filtering the signal. This

approach allows the device to reduce any noise in the measurement that can be caused by noise coupling

into the signal. A greater number of averages enables the device to be more effective in reducing the noise

component of the measurement.

The conversion times selected can also have an impact on the measurement accuracy. Figure 6-2 shows

multiple conversion times to illustrate the impact of noise on the measurement. to achieve the highest accuracy

measurement possible, use a combination of the longest allowable conversion times and highest number of

averages, based on the timing requirements of the system.

Figure 6-2. Noise vs Conversion Time

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INA226

SBOS547B – JUNE 2011 – REVISED SEPTEMBER 2024

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