This article will first introduce the common-mode transient immunity (CMTI) specification and its importance in a system. We will discuss a new isolated sigma-delta modulator family, its performance, and how it improves and facilitates system current measurement accuracy, especially for offset error and offset error drift. Finally, a recommended circuit solution will be introduced.
Isolated modulators are widely used in motors/inverters where high accuracy current measurement and galvanic isolation are required. With the high integration and high efficiency revolution in motor/inverter systems, SiC and GaN FETs are beginning to replace MOSFET and IGBT due to their smaller size, higher switching frequency, and lower heatsink advantages. However, high CMTI capability is required for the isolation components. Higher accuracy current measurement is also needed. The next-generation isolated modulator greatly increases the CMTI capability and improves the accuracy itself.