A Negative-Gm Oscillator With Common Mode Transient Immunity Enhancements For Galvanically Isolated Gate Drivers

This paper presents a Common Mode Transient Immunity (CMTI) enhancement circuit for transformer based galvanically isolated gate drivers with a negative-Gm oscillator. Regardless of the isolation method or structure, the communication path is susceptible to CMTI events due to the inherent parasitic capacitance. The proposed CMTI enhancement concept prevents false turn-OFF events during negative transients by activating a timer-based current source, which maintains the negative-Gm oscillator active. The CMTI enhancement circuit was verified by means of simulations and integrated in a 0.25 $\mu \mathrm{m}$ CMOS technology as part of a galvanically isolated gate driver. Comparative experimental results with the CMTI enhancement circuit disabled and enabled demonstrate increased resilience against negative transients. The proposed solution achieves Common Mode Transient Immunity levels between 1 kV and 150 $\mathrm{k}\mathrm{V}/\mu \mathrm{s}.$