1.2 V Detected on

Channel 1 Bus Voltage

Measurement

Measure For 1.2 V

on Channel 2

Bus Voltage

1.2 V on Channel 2 Detected

1.2 V on Channel 2 Not Detected

Timing

Control

Output

High

Low

28.6 ms

Load 2

Power Supply

(0 V to 26 V)

Ch 1

Ch 2

Ch 3

ADC

”

10

”

10

Ceramic Capacitor

INA3221

www.ti.com

SBOS576 – MAY 2012

Figure 27. Timing Control State Diagram

The Timing Control Alert function is only monitored at power-up or when a software reset is issued by setting the

RESET bit (bit 15) in the Configuration Register. The Timing Control Alert function timing is based on the default

device settings at power-up. Writing to the Configuration Register before the Timing Control Alert function

completes the full sequence results in disabling the Timing Control Alert until power is cycled or a software reset

is issued.

FILTERING AND INPUT CONSIDERATIONS

Measuring current is often noisy, and such noise can be difficult to define. The INA3221 offers several filtering

options by allowing conversion times and the number of averages to be selected independently in the

Configuration Register. The conversion times can be set independently for the shunt and bus voltage

measurements for added flexibility in configuring power-supply bus monitoring.

The internal ADC is based on a delta-sigma (

ΔΣ) front-end with a 500-kHz (±30%) typical sampling rate. This

architecture has good inherent noise rejection; however, transients that occur at or very close to the sampling

rate harmonics can cause problems. Because these signals are at 1 MHz and higher, they can be managed by

incorporating filtering at the INA3221 input. The high frequency enables the use of low-value series resistors on

the filter with negligible effects on measurement accuracy. In general, filtering the INA3221 input is only

necessary if there are transients at exact harmonics of the 500-kHz (±30%) sampling rate (greater than 1 MHz).

Filter using the lowest possible series resistance (typically 10

Ω or less) and a ceramic capacitor. Recommended

capacitor values are 0.1

μF to 1.0 μF. Figure 28 shows the INA3221 with an additional filter added at the input.

Figure 28. INA3221 with Input Filtering

Copyright © 2012, Texas Instruments Incorporated

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Product Folder Link(s): INA3221