−120

−80

−40

0

40

80

120

0

200

400

600

800

1000

Conversion Time: 140µS

Conversion Time: 332µS

Conversion Time: 1.1mS

G023

INA3221

SBOS576 – MAY 2012

www.ti.com

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

Figure 23. Multiple conversion times shown in Figure 23 illustrate the impact of noise on the measurement.

These curves were taken without averaging used. In order to achieve the highest accuracy measurement

possible, a combination of the longest allowable conversion times and highest number of averages should be

used, based on system timing requirements.

Figure 23. Noise versus Conversion Time

ALERT MONITORING

Because the INA3221 allows programmable thresholds that ensure the intended application operates within the

desired operating conditions, multiple monitoring functions are available via four Alert pins: Critical Alert, Warning

Alert, Power Valid Alert, and Timing Control Alert. These Alert pins are open-drain connections.

Critical Alert

The Critical Alert monitors functions based on individual conversions of each shunt voltage channel. The Critical

Alert Limit feature compares the shunt voltage conversion for each channel to the corresponding value

programmed into the corresponding limit register to determine if the measured value exceeds the intended limit.

Exceeding the programmed limit indicates that the current through the shunt resistor is too high. The default

Critical Alert Limit value for each channel is set to a positive full-scale value to effectively disable this alert at

power-up. The corresponding limit registers can be programmed at any time to begin monitoring for out-of-range

conditions. The Critical Alert pin is asserted and pulled low if any channel measurements exceed the limit present

in the corresponding channel Critical Alert Limit. When the Critical Alert pin is asserted, the Mask/Enable

Register can be read to determine which channel caused the Critical Flag Bit to assert.

The INA3221 also allows the Critical Alert pin to be controlled by the Summation Control function. The

Summation Control function compares the sum of the single conversions of the desired channels based on the

Summation Channel Control bits set in the Mask/Enable Register to determine if the combined sum has

exceeded the programmed limit. In order for this summation limit to have a meaningful value, all included

channels must use the same shunt resistor value. The individual conversion values cannot be added directly

together in the Shunt Voltage Sum register to report the total current unless equal shunt resistor values are used

for each channel. The Summation Channel Control bits either disable the Summation Control function or allow

the Summation Control function to switch between including two or three channels in the Shunt Voltage Sum

register. The Shunt Voltage Sum Limit register contains the programmed value used to compare the Shunt

Voltage Sum register to determine if the total summed limit has been exceeded. If the Shunt Voltage Sum Limit

value is exceeded, the Critical Alert pin is asserted low. Either the Summation Flag bit or the individual Critical

Alert Limit bits in the Mask/Enable Register can determine the source of the alert when the Critical Alert pin

asserts.

14

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