SiC MOSFET Gate Drive Requirements
Silicon carbide (SiC) MOSFETs become ever increasing members of the power semiconductor family. SiC MOSFETs (as the name tells) can hold off higher voltage, and have lower conduction losses than their expensive cousins silicon MOSFETs, and so they can switch faster and faster. As the whole world tries to get in on this power conversion business, SiC MOSFETs are the technology of choice for Among other things, power electronics, EVs, photovoltaics, and so on. But let’s assume now that we do wish to drive a SiC MOSFET, just what is the secret ingredient? What is special? What do you need then? Here I review – what are the gate drive requirements of SiC MOSFETs?
What You Should Know about SiC MOSFETs
So first, what is the black magic of the SiC MOSFET? These little darlings are fabricated using silicon carbide (it’s a compound of Si, C which is a wide-bandgap semiconductor. It has good thermal conductivity, and it stands the heat of higher voltages and higher temperatures than silicon. They thus find themselves in applications requiring high efficiency under high power, and often low-volume conditions such as EV inverters and solar inverters, and motor drive and industrial power.Their voltage figuring is much higher than silicon, and they are lower loss (yes, of course), and they switch faster.
This bunching of the geeky good bits means that to get the best of the beasts, the gate drive requires special attention.
Gate Drive Requirements for SiC
As you might expect the gate drive requirements of SiC are:
Gate Drive Voltage
The gate voltage of a SiC is also crucial. In general, SiC MOSFETs will require higher gate drive voltage than silicon MOSFETs as they are wide bandgap devices.
While a normal silicon MOSFET will light up at around 10 to 15 volts, SiC devices generally require 18volts to 20volts for a full on. This greater gate voltage insures the SiC Mosfet is ultimately enhanced, therefore, so that its on resistance (Rds(on)) is as low as can be, reducing conduction losses, but the voltage must also be below the maximum rating permitted by the particular manufacturer of the device to avoid gate oxide damage.
Gate Drive Current
Increasing the gate drive current to switch SiC MOSFETs rapidly requires the gate drive circuit to supply enough current to charge and discharge the gate capacitance. The gate capacitance in a SiC MOSFET is larger than progressively met in a silicon MOSFET, especially at the higher voltages, and so the gate drive circuit will have to provide larger current pulses of a few amperes.The greater the gate drive current the faster the MOSFET will get to its on state, therefore, and the speedier operation will therefore reduce the MOSFET switching losses but will demand, obviously, more powerful gate drivers. The designer must therefore trade the benefit of speed against the power budget allowable such that they do not raise too much heat.
Switching Speed And Gate Charge
We use the term switching speed to convey an impression of just how fast, on average, a given SiC, will turn on/off. The SiC switch will generally be quicker than a silicon MOSFET and specifications will often talk of switching frequencies greater than 100 kHz.
Gained on speed, and controlling acceptable onset speed (the time in which the switch turns on to settles at 50% full on), calls for good gate drive handling.
Gate Charge
Gate charge is a number that represents the total charge that must be transferred to the gate of the MOSFET in order to turn the device on and off successfully. These numbers tend to be much greater for SiC MOSFETs as compared with silicon, and especially for higher voltage ratings. For this reason drive circuits must be accounted to be able to flow enough charge in order to charge/discharge the gate capacitance in whatever switching time is required.
To summarize, in order to obtain fast smart gate drive switching transitions with little power loss, the driver must have a low output impedance and be capable of large peak currents.Any parasitic inductances and capacitances that become part of the gate drive must thus be minimized to obtain fast speeds and reduced losses.
Changing the actual switching losses, minimizing them and allowing the SiC to operate at high frequency is all part of the delight of the technology. Driver circuit design needs to be low loss as there is a switching process actually going on. Making the transition both on and off takes energy, and therefore that energy is related to the charge transacted through the gate, and hence to switching frequency. The only way to cut this loss to the bone is for the gate drive to switch the SiC device on as quickly as it possibly can, but without any ringing and overshoot. The driver circuits have also to ensure as far as possible that for the very short brief time that the SiC device is switching that it is either totally obviously on or off to minimize conduction loss. 2.5 Protection features Protection features which figure highly in a Gate drive for SiC MOSFETs. Common protection features include: Desaturation detection – to warn if mosfet is in saturation region and not turning adequately on – this should be self evident as to be, if is a fault of of the value of the gate drive voltage (gategtv) supplied to it.Overvoltage and Undervoltage Lockout (OVLO and UVLO)
– for the foibles of protecting a made gate for SiC mosfets – if over or under voltage is applied to the gate – it simply doesn’t turn on.Thermal shutdown
– if it gets hot, it’s going to be stopping for you. Avoids the Scary Stuff. If that mosfet does its job and goes on to interface with some other high power hardware, it has to defend itself adequately3Thermal management
if you’re procuring into high power you’re intending to get hot the mosfets as part of their requisite purposes. So the gate driver itself for the SIc’s should be sufficiently distinct as to interface properly with them in a thermal sense, but nevertheless as close as it can get without receiving stray electromagnetic fied effects of the other devices in the circuits (mainly), and thus confine itself bout about for distances accordingly. The monitor qould also ideally be gated into a low on state and measure the mosfet’s junction temp periodically to be fore warned and have an idea of what state of operation its in, for instance, to determine batters so that we know its safe and won’t go pop in device qualify performance from there.Gate driver selection
When dealing with SiC mosfets – selecting the right gate drive for this particular activity(, mainly) is critical. Lots to be thought of – some of these being:Voltage rating – without rambling too long here – if the mosfen’s happy enough to accept a gate voltage any greater than what can be supplied from its gate drive the drive shouln’t be seen to work to try keep it on. Too low and it will neither be helping it switch at your desired current, and you wont get it in its intended state achiev looking at something to see what might be figure above have to saySuffice to say voltage rating matters!Current drive capability – the current within the gate driver supplying the ideal quantity to your mosfets easily otherwise.Package type – possibly determines amount of power per square inch apparently in total, but definitely dictates the circles dimensions etc,,, but can however offer quite tiddy power output too.Go driver you picked of course has to fit in that.Integration – do you have room on the PCB left?Conclusion
Good for you if you made it this far. SiC MOSFET chips offer lots of interesting aspects in terms of quite literally handling voltage, extremely hot heat, and gaining rabid do/flyback response rates at high frequencies. Whenever you need to alone provide it, it will materialise and meet those demands, of many good component suppliers you could assess,or instate to gauge; you can handle a good number of obstacles this way.