Challenges of Short Circuit Protection for Wide Band Gap Power Semiconductor - Richardson RFPD

Short Circuit Protection of WBG (SiC and GaN) power devices

1. Challenges of Short Circuit Protection for Wide Band Gap Power Semiconductor Michele Sclocchi, Application Engineer, Richardson RFPD

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3. SiC Short Circuit Withstand Times Short circuit withstand capability measures the MOSFET’s ability to survive an instantaneous short of the DC link across its drain-source terminals.   SOURCE : *Review and analysis of SiC MOSFETs’ ruggedness and reliability, Jung Wang, Xi Jang, IET Journal 2020 ** Comparison and Discussion on Shortcircuit Protection for SiC MOSFET Modules, Slavko Mocevic IEEE *** An intelligent medium voltage gate driver with enhanced short circuit protection, A. Kumar IEEE 2018 (**) Short Circuit Response time (SCRT) below 2µs is relatively safe for a single SC event Short-circuit withstand time increases with larger device area and MOSFET channel length

4. Typical SiC MOSFET Short-circuit Behavior Ohmic region Saturation region 2.2kV Overshoot *Source: New definition of critical energy for SiC MOSFET robustness under short circuit operation: The repetitive critical energy. Microelectronics Reliability Nov 2020 A Survey of SiC Power MOSFETs Short-Circuit Robustness and Failure mode Analysis, L. Ceccarelli , P.D. Reigonsa , F. Iannuzzo , F. Blaabjerg ** Reducing Size, Noise, and Field Failures of Transportation APUs, Bodo’s Power Dec 2020. Microchip shows a SCWTs between 3 to 14µs with dependence on dc link voltage and applied Vgs . Short Circuit Response time (SCRT) below 2µs is relatively safe for a single Short Circuit event Soft-Turn-Off is adopted to avoid voltage overshoot MOSFET Switched off with Overshoots

5. Destructive Test on SiC Module *Source: Wolfspeed - Analog Device – Driving SiC Campaign I SC = 6,000 A V DC =700 V V GS Device enters saturation Module Damaged Enters saturation ~1 m s Turning-on into a fault Must detect fault in this region Unlike an IGBT, fault on a SiC device may have to be detected before the short-circuit (SC) current reaches a peak (rising portion of SC current) and saturates. In most SiC modules, faults must be detected when the SC current is still rising (<1 µs) and hasn’t saturated. *Test results on a BM3 module

6. Fast Short-Circuit Protection with DeSat Set the Dsat voltage based on the maximum desirable current at 150 ° C Fast reverse recovery Dsat diode with low capacitance Blanking time is tuned to avoid false fault protection to (200-400nsec) The saturation circuit detects the drain to source voltage of MOSFET SOURCE : *ADuM4177 Analog Device ** Comparison and Discussion on Short-circuit Protection for SiC MOSFET Modules, Slavko Mocevic IEEE Fault Under load Desat detect Hard Switching Fault Accuracy expectations limited by the tolerance of the components. Good for short-circuit protection not over-current detection Hard Switching Fault has the highest detection time.

7. Fault Response Time – Hard Switched Fault Gate Driver: ADuM4177 R G(ON) = 1.2 W R G(OFF) = 0.5 W R G(SOFT OFF) = 2.0 W V DESAT = 7V T BLANK =300ns SiC Module: CAB450M12XM3 (1200V / 450 A) 1 2 3 4 5 6 7 MID DC+ DC− Copper Jumper

8. Fault Response Time – Hard Switched Fault Vdc: 800V Blanking time: 400ns SC current 6.2kA Fault detected and Switch turned off in <1 µs Driver: Analog Device ADuM4137 programmable Gate Driver Board SiC MOSFET Module: Wolfspeed WAB400M12BM3 1200V 400A 3.25m Ω half bridge module

9. GaN Short Circuit Withstand Times Short circuit withstand capability of GaN devices are 10 x lower than SiC at DC bus voltage above 400V, and relatively long withstand time from 0V to 350V SOURCE : *Short Circuit Capability and Degradation Mechanism Analysis of E-mode GaN HEMPT, Thesis Xiao Li, Ohio State University GaN devices can deliver much higher power density in smaller areas than conventional silicon devices, therefore with a steeper rise in temperature during short-circuit events resulting in shorter SCWT than silicon-based counterparts.

10. GaN Short Circuit Capability – test results SOURCE : * GaN Systems – Short Circuit Capability test results from GaN Systems Test results from GaN Systems GS66508B 650V 30A 50m Ω 400V short-circuit withstand time of 235ns In 100ns time level, the saturation current is about 160Amps GS66516B 650V 60A 25m Ω The saturation current is about 320A Larger device will have longer withstand time Relatively long withstand time from 0 to 350V Isat is always about 5x larger than the rated current

11. Short Circuit Protection optimized for GaN : * Source: A Simple Desaturation-Based Protection Circuit for GaN HEMT With Ultrafast Response – IEEE June 2021 The Short Circuit Protection for GaN must be ultrafast with a response time less than 300ns with a 650V GaN device: Integrated DESAT detection circuit must be optimized for speed Soft turn-OFF stage to limit the voltage spike on the dc link Si8271GB Isolated Gate Driver GS66516B GaN E-HEMT 650V 25m Ω 60A

12. * Source: AN1288: Si828x External Enhancement Circuit Skyworks Application Note ** SiC MOSFET short-circuit protection using skyworks SI828x Gate Driver – Test Report PRD-02344 Wolfspeed *** Short-Circuit Capability with GaN HEMPTs, Davide Bisi , Bill Cruse Standard DESAT Protection circuits can be enhanced for fast response time << 1 Adding a resistor (RI) in series of a diode to speed up the detection time   US Patent # 109170810 Short Circuit Protection optimized for fast protection response time: DESAT detection time 180nS DESAT response time 370nS

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