Integrated current sensing in GaN power ICs

Integrated current sensors at the drain and source of lateral GaN-on-Si power transistors are presented, using the existing resistive metal fingers of large-area comb-structures as shunts. In comb-structures, the finger current flows orthogonal to the channel current, thus the sensor signal is independent from the dynamic channel resistance. At 1MHz pulsed switching of 75V in a half-bridge converter, the drain and source sensors are characterized (around 4m shunt resistance as part of a 100m transistor) in both high-side and low-side configurations. The measured current sense-ratio temperature coefficient of 0.003/K results mainly from the finger metal and is correctable by integrated linear temperature sensors with a similar coefficient. A readout circuit which proportionally reproduces the continuous external inductor current is implemented by summation of the switched high-side source and low-side drain current sensor signals. Integrated current sensors enable control and protection of GaN HEMTs and ICs, for example in monolithic or copackaged GaN half-bridges.