Automotive Dual Channel SiC MOSFET Gate Driver Reference Design with Two Level Turn-off Protection
Created: Jul 30, 2018
This reference design is an automotive qualified isolated gate driver solution for driving Silicon Carbide (SiC) MOSFETs in half bridge configuration. The design includes two push pull bias supplies for the dual channel isolated gate driver respectively and each supply provides +15V and -4V output voltage and 1W output power. The gate driver is capable of delivering 4A source and 6A sink peak current. It implements reinforced isolation and can withstand 8kV Peak and 5.7kV RMS isolation voltage and >100V/ns common mode transient immunity (CMTI). The reference design contains the two-level turn-off circuit which protects the MOSFET from voltage overshoot during the short circuit scenario. The DESAT detection threshold and the delay time for second stage turn-off are configurable. The ISO7721-Q1 digital isolator is implemented for interfacing the signals of fault and reset. All designed on a two layer PCB board with a compact form factor of 40mm × 40mm.
SiC MOSFETs are gaining popularity in many high-power applications due to their significant advantages of superior switching performance, higher dielectric-breakdown field strength, and higher ambient operating temperatures. The SiC MOSFET has been widely used in high-voltage, high-frequency, power electronic converters in the HEV/EV. Examples are high-voltage PFC converters, LLC, or phase-shifted full-bridge DC/DC converters, bidirectional DC/DC converters, high-voltage Flyback converters, and so on. Challenges are raised in the design of appropriate gate drivers. The characteristics of SiC MOSFETs require consideration of a gate-driver circuit that optimizes the switching performance of the SiC device. • Gate voltage must be kept as high as possible, within the specified range, to operate the devices at a lower Rdson, so that the conduction losses can be minimized. • The gate driver must have a low-propagation delay time and also a fast turn-on and turnoff slew rate. Low turn-on loss (Eon) and turnoff loss (Eoff) allow the device to operate at high-switching frequencies. SiC devices can be turned-on and turned-off within tens of nanoseconds, which largely depends on internal and external gate resistance. • SiC MOSFETs are (normally off) voltage-controlled devices. The off and on gate voltages are normally in the range of 0 V and 20 V, respectively. A negative drive in the order of –5 V is preferred at the time of turning off the device, to ensure faster turnoff and to avoid faulty turn-on due to noise or ringing at the gate. Considering the system requirements, many require reinforced isolation for safety reasons. A half-bridge configuration built in a compact board is usually preferred, because of ease of layout design and reduced parasitics. This reference design features the following benefits: • Compact, dual-channel, gate-driver solution for driving SiC MOSFETs in half-bridge configuration • 4-A source and 6-V sink peak-current driving capability suitable for driving SiC MOSFET, Si MOSFET, and IGBT, with switching frequency up to 500 kHz • Built-in, compact, high-efficiency, isolated-bias supply, with 15 V and –4 V outputs • Flexible and configurable as dual channel in half bridge, in parallel, dual high-side and dual low-side • Gate-driver dead time control with shoot-through protection ensures safe operation • Low-propagation delay ensures easy control and allows increased switching frequency • Discrete, two-level turnoff for short-circuit protection, with adjustable current limit and delay (blanking) time • Provide high CMTI of > 100 kV/µV and reinforced isolation of 8-kV peak and 5.7-kV RMS voltages