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Application Considerations for SiC MOSFETs

January 2011

CPWR-AN08, REV -

Application Considerations for SiC MOSFETs -

January 2011

This document is provided for informational purposes only and is not a warranty or a specification.

For product specifications, please see the data sheets available at www.cree.com/power. For warranty

information, please contact Cree Sales at PowerSales@cree.com.

SiC MOSFET

Figure 1: O

The modest transconductance and short

device. The CMF20120D needs to be driven with a higher gate voltage swing than what is customary

with SJMOSFETS or IGBTs. Presently,

for the CMF20120D. Care needs to be taken not to exceed

of gate voltage will have a greater effect on the rate of rise of the drain current due to the

transconductance. Therefore, the gate drive needs to supply a fast rise and fall time gate pulse to

maximize switching speed. The CMF20120D

(2V nominal). Like the Si SJMOSFET, consideration

especially at high temperatures.

The rather large triode region can have

active de-saturation circuits. Some of these designs assume t

impedance constant current and/or tran

CMF20120D , the output impedance is lower and the

region during this type of over-current fault

drain to source voltage will not increase as much

carefully considered in fault protection schemes.

The forward conduction characteristics of the

IGBTs are presented in Figure 2. T

were somewhat similar. At 150 °C,

°C to 150 °C, whereas both the Si SJMOSFET and Si MOS8 devices

significant effect on system thermal design. The obvious advantage is that a smaller device can be used

at higher operating temperatures.

2

Si NPT IGBT

ance and short-channel effects are important to consider when applying the

needs to be driven with a higher gate voltage swing than what is customary

with SJMOSFETS or IGBTs. Presently, a +20V and -2V to -5V negative bias gate drive is recommended

Care needs to be taken not to exceed -5V in the negative direction

of gate voltage will have a greater effect on the rate of rise of the drain current due to the

transconductance. Therefore, the gate drive needs to supply a fast rise and fall time gate pulse to

CMF20120D also has a threshold voltage similar to the Si SJMOSFET

(2V nominal). Like the Si SJMOSFET, considerations need to be made for the lower threshold voltage,

have an impact on certain types of fault detection schemes, chiefly the

saturation circuits. Some of these designs assume that the switching device enters a fairly high

and/or transconductance saturation region during over-current

, the output impedance is lower and the device does not go into a clean constant current

current fault, especially under moderate over-currents. Therefore, the

not increase as much. These characteristics of the SiC MOSFET need

carefully considered in fault protection schemes.

The forward conduction characteristics of the CMF20120D along with the Si SJMOSFET,

The Si SJMOSFET’s relatively high positive temperature coefficient of

considerable effect on its conduction losses. At 25 °C, the Si SJMOSFET and

whereas both the Si SJMOSFET and Si MOS8 devices increase by 250%.

significant effect on system thermal design. The obvious advantage is that a smaller device can be used

Si NPT IGBT

channel effects are important to consider when applying the

needs to be driven with a higher gate voltage swing than what is customary

gate drive is recommended

5V in the negative direction. The rate of rise

of gate voltage will have a greater effect on the rate of rise of the drain current due to the lower

transconductance. Therefore, the gate drive needs to supply a fast rise and fall time gate pulse to

also has a threshold voltage similar to the Si SJMOSFET

s need to be made for the lower threshold voltage,

impact on certain types of fault detection schemes, chiefly the

hat the switching device enters a fairly high

current faults. For the

device does not go into a clean constant current

. Therefore, the

. These characteristics of the SiC MOSFET need to be

Si SJMOSFET, TFS, and NPT

temperature coefficient of

Si SJMOSFET and CMF20120D

only about 20% from 25

ase by 250%. This has a

significant effect on system thermal design. The obvious advantage is that a smaller device can be used