Cascoded GaN half-bridge with 17-MHz wide-band galvanically isolated current sensor
Abstract A cascoded GaN half-bridge with wide-band galvanically isolated current sensor is proposed. A 650-V depletion-mode GaN FET is switched by a low-propagation-delay gate driver in active-mode. The standby and active modes are switched by a 25-V N-ch LDMOS. The current sensor uses the LDMOS as a shunt resistor, gm-cell-based sense amplifier and mixer based isolation amplifier for wider bandwidth. PVT variations of on-resistance of the current-detecting MOSFET are compensated using a reference MOSFET. A digital calibration loop across the isolation is formed to keep the current sensor gain constant within ±1.5% across the whole temperature range. The wide-band current sensor can measure power device switching current. In this study, a cascoded GaN half-bridge switching and inductor current sensing using low-side and high-side device current are demonstrated. The proposed techniques show the possibility of implementing a GaN half-bridge module with isolated current sensor in a package.
