Datasheet
Load 2
Power Supply
(0 V to 26 V)
Ch 1
Ch 2
V
IN
2
V
IN+2
Ch 3
ADC
R
FILTER
” 10
R
FILTER
” 10
C
FILTER
: 0.1-µF to 1-µF
Ceramic Capacitor
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
INA3221
www.ti.com
SBOS576A –MAY 2012–REVISED JUNE 2013
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
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