Pairing Gate Driver Performance with ISO 26262 Functional Safety Requirements

Abstract:
The challenges for a SiC-MOSFET and IGBT gate driver in automotive applications have increased due to three main factors. First, DC-Link voltage is higher due to higher battery voltages in Battery Electric Vehicles (BEVs) and commercial vehicles making safe operation of power semiconductors a more demanding task. As an example, the 800V battery voltage results in DC-Link voltages in the traction converter of up to 950V in operation, which in turn results in less margin when implementing safe turn-off of 1200V SiC-MOSFET and IGBT modules. The second factor is Functional Safety (FuSa). FuSa requirements according to ISO 26262 and the resulting Automotive Safety Integrity Level (ASIL) requirements up to Level D apply. The third factor is the requirement for interference immunity — a big challenge due to the compact designs of the converters and increasing dv/dt of the power semiconductors especially when using SiC-MOSFETs. In addition to interference immunity, the galvanic isolation between the primary side (low voltage) and secondary side (high voltage), as well as between the upper and lower power semiconductor switch, must be addressed. Associated with increased voltage are higher clearance and creepage distances, as well as the partial-discharge properties of the insulation material. Almost all customers require reinforced electrical isolation according to IEC 60664 for a 1000V system. The high-voltage insulation creates a coupling capacitance that is stressed by the dv/dt of the switching power semiconductors as well as by the di/dt of the load current. The Common Mode Transient Immunity (CMTI) characteristics of the isolation barrier and its upstream and downstream components must be considered