Gate Drive — Wolfspeed Power Applications Forum

[FAQ-GD-5] How can I control the turn-on and turn-off slew rate?

TBhatia — Wed, 01 Feb 2023 15:29:27 +0000

The slew rate is easily controlled with an external gate resistor between the gate driver and SiC MOSFET gate. The higher the value of the resistor, the slower the slew rate will be, but the switching losses will increase. This is a design tradeoff between EMI (dv/dt) and switching losses.

[FAQ-GD-4] Do I need short-circuit protection? How is it different than IGBT desat protection?

TBhatia — Wed, 01 Feb 2023 03:09:14 +0000

The need for short-circuit protection depends on the application and reliability requirements. SiC MOSFETs are capable of withstanding several microseconds of short circuit conditions (MOSFET gated on with minimal resistance or inductance to limit the rate of current rise) where the drain current rises very quickly. However, in order to prevent damage to the MOSFET, the fault condition must be detected and the MOSFET turned off quickly.

Although SiC MOSFETs do not exhibit desaturation behavior like IGBTs, the voltage across the drain to source of the part will increase as the current increases. Therefore, a circuit very similar to an IGBT desat detection circuit can be used to detect the fault condition. The voltage levels and timing requirements are different for SiC MOSFETs. We have worked closely with our gate driver partners at Analog Devices, Skyworks, Texas Instruments, NXP, and Broadcom to develop robust short-circuit protection solutions. Please contact your FAE for additional resources regarding short-circuit protection.

[FAQ-GD-3] Can Wolfspeed C3M MOSFETs operate at Vgs(off)= 0V to be compatible with other suppliers?

TBhatia — Wed, 01 Feb 2023 02:53:45 +0000

Wolfspeed C3M MOSFET’s can be fully turned off at 0V. We recommend negative voltage turn-off for half bridge configuration where the cross talk can potentially cause parasitic turn-on under hard-switching condition. Negative turn-off voltage can guarantee the voltage spike on the gate will not go above the gate threshold voltage during switching transition so that there is no shoot through in half bridge configuration.

For common single switch topologies like Boost, Buck, Flyback converters or other topologies with no risk of parasitic turn-on, it is fine to use 0V for turn-off.

[FAQ-GD-2] Can Wolfspeed C3M MOSFETs operate at Vgs= +18V to be compatible with other suppliers?

TBhatia — Wed, 01 Feb 2023 02:40:07 +0000

Wolfspeed C3M MOSFET’s have been thoroughly optimized for Vgs(+)= 15V operation and the benefits of operating at Vgs(+)=18V are minimal. Furthermore, operation at Vgs(+)> 15V causes unnecessary gate stress which we do not recommend. Wolfspeed has worked with our partners to develop drivers optimized for Vgs=15V/-4V operation. While a Vgs(+)=15V gate drive circuit is always recommended, Wolfspeed has prepared some simple power supply design options for interoperability between various positive and negative Vgs voltages.

[FAQ-GD-1] How can I generate the gate drive bias needed for SiC MOSFET's

SiC_Power_Admin — Thu, 05 Aug 2021 19:20:24 +0000

Wolfspeed C3M SiC MOSFET's require a gate drive voltage of +15V/-4V which can be generated using several different methods. An Application Note that discusses the various techniques along with the pro's and cons's of each will be available on Wolfspeed.com soon. Some additional notes on the methods is below :

An off-the-shelf isolated DC/DC power supply from Murata, Mornsun or Recom is the simplest way to generate the required bias.The Wolfspeed evaluation board CGD15SG00D2 demonstrates application of the the Murata module MEJ2D1209SC for generation of +15V/-3V gate drive voltage.
A discrete design can provide a more cost effective solution, flexible and smaller form factor at a low cost. One example can be found in the Texas Instruments reference design - TIDUE55B .