AVG #

÷

New

Sample

-

+

+

+

Output

Register

20

21

22

23

24

25

26

1000

2000

3000

4000

5000

6000

7000

Samples

1 Average

16 Averages

1024 Averages

G020

INA3221

SBOS576 – MAY 2012

www.ti.com

INA3221 AVERAGING FUNCTION

The INA3221 includes three channels to monitor up to three independent supply buses. Multichannel monitoring

potentially results in poor shunt resistor placement. Ideally, the shunt resistors should be located as close as

possible to the corresponding channel input pins. However, because of system layout and multiple power-supply

rails, one or more shunt resistors may have to be located further away from the INA3221 than they otherwise

ideally would be, thus presenting potentially larger measurement errors. These errors can result from additional

trace inductance and other parasitic impedances between the shunt resistor and input pins. Longer traces also

create an additional potential for coupling noise into the signal if they are routed near noise-generating sections

of the board. The INA3221 averaging function mitigates this potential problem by limiting the impact any single

measurement has on the averaged value of each measured signal. This limitation reduces the influence noise

has on the averaged value, thereby effectively creating an input signal filter.

The averaging function is described in Figure 21. The INA3221 operation begins by first measuring the shunt

input signal on channel 1. This value is then subtracted from the previous value that was present in the

corresponding data output register. This difference is then divided by the value programmed by the Averaging

Mode setting (Configuration Register bits[11:9]) and stored in an internal accumulation register. The computed

result is then added to the previously-loaded data output register value and that resulting value is loaded to the

corresponding data output register. After the update, the next signal to be measured follows the same process.

The larger the value selected for the averaging mode setting, the less impact or influence any new conversion

has on the average value, as shown in Figure 22. This averaging feature functions as a filter to reduce input

noise from the averaged measurement value.

Figure 21. Averaging Function Block Diagram

Figure 22. Average Setting Example

12

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