INA219

No. The INA219 measures the voltage across an external shunt that you place in the bus; TI specifies a shunt full-scale input range of ±40 mV, ±80 mV, ±160 mV or ±320 mV set by the PGA. The 0.1 Ω figure everyone quotes comes from the popular breakout boards, which fit a 0.1 Ω 1 percent shunt on the PCB — with the ±320 mV range that gives 3.2 A full scale. If you are designing your own board, select the shunt so that maximum current produces a drop inside your chosen PGA range, and remember the shunt's own tolerance and temperature coefficient add directly to your measurement error.

The INA226 is the upgrade: 36 V bus range instead of 26 V, 16-bit converters instead of 12-bit, lower offset and better gain accuracy, and an alert pin with programmable limits. The register map is similar but not identical, so firmware changes are needed. Use the INA219 where the 26 V bus ceiling is comfortable, cost matters and 12-bit resolution (10 µV shunt LSB) is enough; use the INA226 for 24 V industrial rails with margin, 48 V systems or high-precision power accounting. For very high currents look at the INA240 or INA250 family, which integrates the shunt.

Same package, register map and functionality; the B grade has tighter DC accuracy. At PGA ÷1 the maximum input offset voltage is ±100 µV for the INA219A and ±50 µV for the INA219B, and TI publishes the B grade with 0.5 percent maximum accuracy over temperature versus wider limits for the A. Offset drift and PSRR are the same class. The price difference is small, so specify INA219B for new designs — particularly when your shunt is small (for example 5 mΩ to 20 mΩ) and offset becomes a significant fraction of the measured signal.

Follow TI's procedure. Choose your shunt R_SHUNT and the maximum expected current I_MAX. Set Current_LSB = I_MAX / 2^15 (round up to a clean number), then Cal = 0.00512 / (Current_LSB × R_SHUNT), and Power_LSB = 20 × Current_LSB. Write Cal to register 0x05, configure BRNG, PGA, BADC/SADC and MODE in register 0x00, and afterwards the current register (0x04) returns amperes directly as a signed value and the power register (0x03) returns watts. Worked example: with R_SHUNT = 0.1 Ω and I_MAX = 3.2 A, Current_LSB = 100 µA and Cal = 512.

Sixteen addresses are available from 0x40 to 0x4F, selected by strapping A0 and A1 to ground, VS, SDA or SCL in the four combinations TI lists in the datasheet — 0x40 is the common default with both pins grounded. That means up to 16 INA219 devices on a single bus, which is why the part is popular in multi-rail servers and battery packs with per-cell monitoring. The bus runs at up to 400 kHz in fast mode or 2.56 MHz in high-speed mode. Since there is no device-ID register, always verify addressing by reading the configuration register back.

That is set by your shunt, not by the device: the constraint is the shunt voltage, which must stay inside ±320 mV at PGA ÷8. With the 0.1 Ω shunt on typical breakout boards that is 3.2 A. Drop to 0.01 Ω and the same range gives 32 A; use 5 mΩ for 64 A. At those currents shunt self-heating dominates the error budget, so specify a low-TCR alloy shunt (manganin or a metal-strip part), Kelvin-connect the INA219 inputs to the inner edges of the shunt pads, and derate the shunt for the ambient temperature inside the enclosure. Above roughly 100 A, consider a Hall-effect sensor such as the ACS758 or a dedicated integrated-shunt monitor.

Yes — this is a bidirectional monitor. The shunt voltage channel is sign-extended, so current flowing in either direction is reported correctly, and the current register returns a two's complement value. That makes it suitable for battery charge and discharge monitoring, regenerative braking, solar MPPT and any application where power flows both ways. Make sure the bus voltage channel is wired so that IN- sits on the load side of the shunt as shown in the datasheet, since bus voltage is measured at IN- with respect to ground and the common-mode range must stay within 0 V to 26 V.

Because the register map has no ID field, screen electrically: measure quiescent current (0.7 mA to 1 mA active, 6 µA to 15 µA in power-down), apply a known millivolt source across IN+ and IN- and verify the shunt register against the 10 µV LSB, check that offset stays inside ±100 µV (A grade) or ±50 µV (B grade), and confirm the address strapping works. Physically check laser marking on the SOIC-8, lead finish and date-code traceability to TI. MOQ is 2,500 pcs on tape-and-reel for INA219AIDR or INA219BIDR, or 100 pcs loose; TI authorized channel lead time is typically 8-14 weeks and Shenzhen stock ships in 1-3 days.