Overview

The INA3221 is a triple-channel, high-side current and bus voltage monitor IC manufactured by Texas Instruments. Mounted on a purple or black breakout board with 3 sets of screw terminal blocks, it measures current, voltage, and power across three independent power rails simultaneously (e.g., monitoring 3.3V, 5V, and 12V rails in a single system).

Equipped with three onboard 0.1 Ω (100 mΩ)0.1\ \Omega\ (100\ \text{m}\Omega) precision shunt resistors, the INA3221 measures bus voltages from 0V0\text{V} to 26V26\text{V} DC and bi-directional current up to ±3.2 Amperes\pm 3.2\text{ Amperes} per channel with 13-bit ADC resolution. It communicates over an I2CI^2C bus (0x40 default, configurable to 4 addresses) and includes hardware alert outputs (CRITICAL, WARNING).

Quick reference

Operating voltage (VCC)2.7 V to 5.5 V DC (3.3 V or 5.0 V nominal)
Monitored bus voltage (VBUS)0 V to 26 V DC (across all 3 channels)
InterfaceI2CI^2C / SMBus (up to 2.4 MHz)
Default I2CI^2C address0x40 (Configurable 0x40 to 0x43 via A0 pin)
Number of channels3 independent high-side measurement channels
Onboard shunt resistors0.1 Ω (100 mΩ)0.1\ \Omega\ (100\ \text{m}\Omega) per channel
Max current range±3.2 A\pm 3.2\text{ A} per channel (±163.84 mV\pm 163.84\text{ mV} shunt voltage)
Shunt ADC resolution13-bit (40 μV40\ \mu\text{V} LSB voltage step)
Bus ADC resolution13-bit (8 mV8\text{ mV} LSB voltage step)
Hardware AlertsCRITICAL, WARNING, PV (Power Valid) open-drain output pins

Pinout

Breakout board header & Terminal Blocks:

PinNameTypeDescription
1VCCPowerSupply power input (+2.7 V to +5.5 V DC)
2GNDPowerGround reference (0 V)
3SCLDigital InputI2CI^2C Serial Clock
4SDADigital Input / OutputI2CI^2C Serial Data
5A0Digital InputI2CI^2C Address Selection pin
6CRIDigital OutputActive-Low Critical Over-Current Interrupt
7WARDigital OutputActive-Low Warning Over-Current Interrupt
8PVDigital OutputPower Valid Status Output
CH1, CH2, CH3Screw TerminalsPower Input/OutputHigh-side current sensing terminals for Rails 1, 2, 3

Specifications

ParameterSymbolMinTypMaxUnitConditions
Supply VoltageVCCV_{CC}2.73.3 / 5.05.5VDC
Active Supply CurrentICCI_{CC}—350550µAActive 3-channel sampling
Power-Down CurrentIpdI_{pd}—5.010.0µASoftware shutdown mode
Bus Voltage RangeVBUSV_{BUS}0—26VCommon-mode input range
Max Shunt VoltageVSHUNTV_{SHUNT}-163.84—+163.84mVFull-scale differential input
Shunt Voltage LSBLSBshuntLSB_{shunt}—40—µV13-bit ADC step
Bus Voltage LSBLSBbusLSB_{bus}—8—mV13-bit ADC step

Math & Current Calculations

With the factory-installed RSHUNT=0.1 ΩR_{SHUNT} = 0.1\ \Omega:

  1. Calculate Channel Current (ICHI_{CH}):

ICH (A)=VSHUNTRSHUNT=VSHUNT (mV)100 mΩI_{CH}\text{ (A)} = \frac{V_{SHUNT}}{R_{SHUNT}} = \frac{V_{SHUNT}\text{ (mV)}}{100\ \text{m}\Omega}

  1. Calculate Channel Power (PCHP_{CH}):

PCH (W)=VBUS (V)×ICH (A)P_{CH}\text{ (W)} = V_{BUS}\text{ (V)} \times I_{CH}\text{ (A)}

Wiring

INA3221 Pin→Arduino / MCUESP32Notes
VCC5V / 3.3V3.3VPower rail
GNDGNDGNDSystem ground
SCLA5GPIO 22I2CI^2C Clock
SDAA4GPIO 21I2CI^2C Data

Example (Beelan INA3221 Arduino Library)

cpp
#include <Wire.h>
#include <INA3221.h>

// Set I2C Address 0x40
INA3221 ina3221(INA3221_ADDR40_GND);

void setup() {
  Serial.begin(115200);
  Wire.begin();

  Serial.println("TI INA3221 Triple Power Monitor Test");

  ina3221.begin();
  ina3221.reset();
}

void loop() {
  for (int ch = 1; ch <= 3; ch++) {
    float busVolts = ina3221.getBusVoltage(ch);
    float current_mA = ina3221.getCurrent_mA(ch);

    Serial.print("CH"); Serial.print(ch);
    Serial.print(" Voltage: "); Serial.print(busVolts); Serial.print(" V | ");
    Serial.print("Current: "); Serial.print(current_mA); Serial.println(" mA");
  }

  Serial.println("----------------------------------------");
  delay(2000);
}

Common mistakes

  • Leaving shared ground jumper traces un-isolated: Some generic purple INA3221 breakout boards ship with the negative terminals of all 3 channels pre-bridged together to system GND on the PCB traces. If monitoring 3 isolated power supplies with different ground references, cut the GND trace jumpers between channels on the back of the PCB.
  • Forgetting address collision with 0x40: 0x40 is shared by HDC1080, HTU21D, and INA219. Pull A0 to VCCV_{CC} to change INA3221 to 0x41.

Notes

  • INA3221 vs INA219 vs INA226: INA3221 monitors 3 channels up to 26V; INA219 monitors 1 channel up to 26V; INA226 monitors 1 channel up to 36V with 16-bit resolution.

Assets & downloads