Figure 8-1 shows a simplified schematic of the AMC3311 in a typical motor drive application. The DC link voltage is divided down to an approximate 2-V level across the bottom two sense resistors (RSNS1 + RSNS2) of a high-impedance resistive divider. This voltage is sensed by the AMC3311. The AMC3311 digitizes the analog input signal on the high-side, transfers the data across the isolation barrier to the low-side, and reconstructs an analog signal that is presented as a differential voltage on the output pins OUTN and OUTP.

Figure 8-1 The AMC3311 in a Motor Drive Application

The AMC3311 integrates an isolated power supply for the high-voltage side and therefore is particularly easy to use in applications that do not have a high-side supply readily available. In this example, the integrated power supply of the AMC3311 is also used to power an AMC23C11 isolated, high-speed comparator that is used for low-latency overvoltage detection on the DC link.

The AMC23C11 isolated comparator senses the voltage across the bottom resistor (RSNS2) of the resistive divider and compares that value against an adjustable reference voltage (V_REF). The isolated comparator pulls down the open-drain output on the low-side whenever the input voltage exceeds the reference value. For a detailed description of the isolated comparator, see the AMC23C11 data sheet available for download at ti.com.

The bottom resistor in the resistive divider is split into two equal-value resistors (RSNS1 and RSNS2) to accommodate the headroom requirements of the reference voltage (V_REF) of the isolated comparator, as explained in the Detailed Design Procedure section.