In each case, an internal ΣΔ ADC measures current across an integrated sensing resistor, as well as voltage and temperature – communication with the host if via I2C. The ICs need a separate supply of between 2.7 and 5.5V (640µA typ, 5µA max shut-down), and will operate across -40 to +125°C.
Taking the INA781 as an example, the ADC is 20bit.
“The INA781 reports current, bus voltage, die temperature, power, energy and charge accumulation while performing the needed calculations in the background,” said TI. “The integrated temperature sensor is ±2.5°C accurate over the junction temperature range. The low offset and gain drift design allows the device to be used in precise systems that do not undergo multi-temperature calibration during manufacturing.”
The internal resistor is a four-wire sensor (see diagram) with ~535μΩ in the current path, of which nominally 400μΩ produced its output voltage. The measurement system is pre-calibrated to its sense resistor and temperature compensated during operation.
Maximum continuous current is ±75A at 25°C, and although measurement runs out with ±78.64A peaks, higher peaks can be withstood for short periods.
An internal oscillator trimmed to better than 0.5% is used to time ADC conversions and act as a time-base for energy and charge calculations.
In-built digital filter response varies with conversion time, “therefore the precise clock ensures filter response and notch frequency consistency across temperature”, said the company.
ADC conversion times from 50µs to 4.12ms are provided, as well as 1x to 1,024x sample averaging for noise reduction.
Offset current is ±5.5mA max, with ±25µA/°C max drift. System gain error is ±0.5% at 50A, with ±25ppm/°C typical drift. Maximum common-mode rejection is ±100µA/V, and maximum input bias current is 2.5nA.
Power monitoring accuracy is ±0.6%, and both energy and charge accuracy are ±1.1% (all at 25°C, full scale).
Packaging for the INA781 is 6 x 6mm WSON 15, and the similar INA741 comes in a 5 x 43mm QFN 14 and has a ±35A 800µΩ shunt.
With 16bit converters, other new devices in the family are: INA780x, INA740x (800µΩ shunt), INA745x (40V, 800µΩ shunt) and INA700 (40V, 2mΩ 15A).
Applications are foreseen in power delivery, grid infrastructure, industrial batteries, test equipment, telecom equipment and enterprise servers.
The INA781 product page can be found here
