Investigating GaN power device double-pulse testing efficacy in the face of VTH-shift, dynamic Rdson, and temperature variations

Double-pulse testing is widely used in the power-electronics industry for rapid evaluation of power devices. These tests aim to allow observation of how a power device under test (DUT) would behave in real-world continuous-mode operation, without having to operate a full converter. It is well known that several device parameters are temperature-dependent, and for full accuracy, in the double-pulse test the temperature of the DUT must be controlled such that it matches the temperature(s) expected in real-world operation. Further and more challenging complications arise if a GaN (Gallium nitride) transistor is being tested, as these suffer from electron/hole trapping between different layers of the device (e.g., p‑GaN, GaN, AlGaN), which can modulate the gate voltage threshold (VTH) up or down, and give rise to the phenomenon known as dynamic Rdson. This paper reviews the factors that give rise to these dynamic effects in the two main families of normally-off p‑gate GaN power transistors: Schottky-gate and ohmic-gate. Experiments performed with a 400 V, 2 kW-rated converter, whose power devices are mounted on a daughter-board so they can be interchanged without affecting the power board, demonstrate the types and levels of discrepancy to be expected between double-pulse testing and continuous-mode operation. Modification of the double-pulse test to an N-pulse test is proposed, and it is shown that this new test method can reproduce the waveforms seen during continuous operation.