The document describes a fully isolated current sensing circuit with built-in isolated power supply, which has strong robustness and precise measurement capabilities.
The CN-0280 is a fully isolated current sensing circuit designed for use in solar photovoltaic (PV) inverter systems. It features an integrated isolation power supply and is engineered to provide accurate current measurement in high-voltage environments, such as those found in grid-tied inverters where peak AC voltages can reach hundreds of volts. The circuit utilizes a 1 mΩ shunt resistor and a dual-channel AD8639 amplifier to measure currents ranging from a few mA up to 25 A (or higher with adjusted gain).
The core of the design relies on the AD7401A isolated Σ-Δ modulator, which converts the analog input signal into a high-speed 1-bit data stream. This stream is processed by a DSP or FPGA using a sinc3 digital filter to reconstruct the original information. The circuit also incorporates the ADuM6000 isolated DC-DC converter to provide the necessary 5 V power across the isolation barrier, ensuring safety and signal integrity while minimizing EMI/RFI effects.