The INA740x operates off a 2.7 V to 5.5 V supply but can measure voltage and current on rails as high as 85 V. The current is measured by sensing the voltage drop across an internal shunt resistor. The input stage of the INA740x is designed such that the input common-mode voltage can be higher than the device supply voltage, V_S. The common-mode voltage range at the inputs is –0.1 V to +85 V to support both high-side and low-side current measurements. There are no special considerations for power-supply sequencing because the common-mode input range and device supply voltage are independent of each other; therefore the bus voltage can be present with the supply voltage off (and vice-versa) without damaging the device.

The device also measures the bus supply voltage through the VBUS pin and temperature through the integrated temperature sensor. The current is calculated from the voltage drop across the internal shunt resistor which is sensed by the IN+ and IN– pins, while the bus voltage is measured with respect to device ground. Monitored bus voltages can range from 0 V to 85 V, while monitored temperatures can range from –40°C to +150°C.

Shunt voltage, bus voltage, and internal temperature measurements are multiplexed internally to a single ADC (see Figure 6-6).

Figure 6-6 High-Voltage Input Multiplexer