Isolated amplifiers are widely used for voltage measurements in high-voltage applications that must be isolated from a low-voltage domain. Typical applications are AC line voltage measurements, either line-to-neutral or line-to-line in grid-connected equipment.

Figure 8-1 illustrates a simplified schematic of an onboard charger (OBC) application that uses three AMC1350-Q1 devices to measure the AC line voltage on each phase of a three-phase system. The AC line voltage is divided down to an approximate ±5-V level across the bottom resistor (RSNS) of a high-impedance resistive divider that is sensed by the AMC1350-Q1. The output of the AMC1350-Q1 is a differential analog output voltage proportional to the input voltage but is galvanically isolated from the high-side by a reinforced isolation barrier. A common high-side power supply (VDD1) for all three AMC1350-Q1 devices is generated from the low-side supply (VDD2) of the system by an isolated DC/DC converter circuit. A low-cost solution is based on the push-pull driver SN6501-Q1 and a transformer that supports the desired isolation voltage ratings.

The high-impedance input, high input voltage range, and the high common-mode transient immunity (CMTI) of the AMC1350-Q1 ensure reliable and accurate operation even in high-noise environments.