PCB-Integrated Pickup-Coil for Overcurrent Detection in High-Current, Paralleled GaN HEMTs

In this work an easy to integrate and low-cost solution for an overcurrent detection in a high-current half-bridge module based on paralleled 100V, 7mΩ GaN HEMTs is presented. The overcurrent detection is realized with a simple pickup-coil which is integrated into the carrier PCB adjacent to the GaN transistors. The pickup-coils have a sensitivity of around 12mV/A, which results in a peak voltage of above 1.5V at 111A switched current and is twice as high as the peak voltage at the rated current of 50A per HEMT. By a comprehensive finite element s-parameter simulation up to 3GHz, the main coupling parameters between the pickup-coils and the surrounding structures are identified. For lower frequencies below 100MHz an inductive coupling between transistor and pickup-coil is higher, while for higher frequencies the capacitive coupling between inlay and pickup-coil is dominanting. A simple signal evaluation circuit based on an integration amplifier and a fast comparator is presented, which allows a very fast and reliable detection of overcurrent events in 24ns. The presented pickup coil has a significantly increased sensitivity to parasitic effects and coupling due to the high bandwidth of above 400MHz, but demonstrates a very simple implementation and shows the advantages of a non-invasive measurement and scalability for higher voltage classes.