INA3221 datasheet(11/50 Pages) TI2

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7.3 Feature Description

7.3.1 Basic ADC Functions

The INA3221 performs two measurements on up to three power supplies of interest. The voltage developed from

the load current passing through a shunt resistor creates a shunt voltage that is measured between the IN+ and

IN– pins. The device also internally measures the power-supply bus voltage at the IN– pin for each channel. The

differential shunt voltage is measured with respect to the IN– pin, and the bus voltage is measured with respect

to ground.

The INA3221 is typically powered by a separate power supply that ranges from 2.7V to 5.5V. The monitored

supply buses range from 0V to 26V.

CAUTION

Based on the fixed 8mV bus-voltage register LSB (for any channel), a full-scale register value results

in 32.76V. However, the actual voltage applied to the INA3221 input pins must not exceed 26V.

There are no special power-supply sequencing considerations between the common-mode input ranges and the

device power-supply voltage because each are independent of the other; therefore, the bus voltages can be

present with the supply voltage off and reciprocally.

The INA3221 takes two measurements for each channel: one for shunt voltage and one for bus voltage.

Each measurement can be independently or sequentially measured, based on the mode setting (bits 2-0 in

the Configuration register). When the INA3221 is in normal operating mode (that is, the MODE bits of the

Configuration register are set to 111), the device continuously converts a shunt-voltage reading followed by a

bus-voltage reading. This procedure converts one channel, and then continues to the shunt voltage reading of

the next enabled channel, followed by the bus-voltage reading for that channel, and so on, until all enabled

channels have been measured. The programmed Configuration register mode setting applies to all channels.

Any channels that are not enabled are bypassed in the measurement sequence, regardless of mode setting.

The INA3221 has two operating modes, continuous and single-shot, that determine the internal ADC operation

after these conversions complete. When the INA3221 is set to continuous mode (using the MODE bit settings),

the device continues to cycle through all enabled channels until a new configuration setting is programmed.

The Configuration register MODE control bits also enable modes to be selected that convert only the shunt or

bus voltage. This feature further allows the device to fit specific application requirements.

In single-shot (triggered) mode, setting any single-shot convert mode to the Configuration register (that is, the

Configuration register MODE bits set to 001, 010, or 011) triggers a single-shot conversion. This action produces

a single set of measurements for all enabled channels. To trigger another single-shot conversion, write to the

Configuration register a second time, even if the mode does not change. When a single-shot conversion is

initiated, all enabled channels are measured one time and then the device enters a power-down state. The

INA3221 registers can be read at any time, even while in power-down. The data present in these registers are

from the last completed conversion results for the corresponding register. The conversion ready flag bit (Mask/

Enable register, CVRF bit) helps coordinate single-shot conversions, and is especially helpful during longer

conversion time settings. The CVRF bit is set after all conversions are complete. The CVRF bit clears under the

following conditions:

1. Writing to the Configuration register, except when configuring the MODE bits for power-down mode; or

2. Reading the Mask/Enable register.

In addition to the two operating modes (continuous and single-shot), the INA3221 also has a separate selectable

power-down mode that reduces the quiescent current and turns off current into the INA3221 inputs. Power-down

mode reduces the impact of supply drain when the device is not used. Full recovery from power-down mode

requires 40µs. The INA3221 registers can be written to and read from while the device is in power-down mode.

The device remains in power-down mode until one of the active MODE settings are written to the Configuration

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INA3221

SBOS576C – MAY 2012 – REVISED SEPTEMBER 2025

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