# Why is increasing gate voltage beyond 'reasonable' limits not advantageous in power MOSFETs?

In a power MOSFETs datasheet I see Rds(on) specified at Vgs= +10V whereas +Vgs (absolute max) is +30V. Why do they (manufacturers) restrict to +10V while quoting Rds(on)? The manufacturer could have boasted a lower Rds(on) if they quoted at a higher Vgs.

Is +10V kept as a standard for easier comparison? Is there a diminishing return post +10V?

Is there anything I should worry about if I drive Vgs at +15V or +20V?

Wiki says ".., a high gate to source voltage reduces significantly the lifetime of the MOSFET, with little to no advantage on RDSon reduction."

• Fig. 2 in your datasheet shows that Rds saturates to a constant value above 10v, so going higher will not help. Feb 14, 2022 at 15:22

Why do they (manufacturers) restrict to +10V while quoting Rds(on)?

Reasons against

• If you operate this MOSFET at high speeds then turning off the MOSFET requires discharging the 2.45 nF G-S capacitance from nearly 30 volts down to below 3.0 volts ($$\V_{GS(THRESHOLD)}\$$) and that can significantly slow down the switching if you don't use a powerful gate driver.
• Why bother specifying at 20 volts or 30 volts when the data sheet graphs can tell you what the likely improvement in $$\R_{DS(ON)}\$$ is at higher drive levels like 15 volts. Admittedly it's not 30 volts, but, the gains to be made are meagre or small: -

• You can estimate $$\R_{DS(ON)}\$$ (at higher G-S voltages) to a reasonable degree of accuracy using the graphs in the data sheet
• It's common practice to use 10 volts as a reference drive level so that easy comparison can be made with other MOSFETs.

Is there a diminishing return post +10V?

Look at the graphs above - I'd say there was a significant diminishing return. Remember also that this device is targeted at high frequency applications so it's a compromise on how strongly you drive the MOSFET (conduction losses) versus how quickly you can drive it from one state to the other (switching losses): -

Is there anything I should worry about if I drive Vgs at +15V or +20V?

I would have to have good reasons to want to exceed this graph in the data sheet: -

I might initially consider a 15 volts G-S drive level but, I'd also be mindful that if the MOSFET junction temperature rose towards 175°C, it could take an excessive drain current in some circumstances. So, I'd probably end up restricting my drive level to 12 volts in the end.

• Something seems to have gotten a bit confused at the end of this answer. Your last point about not wanting to drive Vgs above 12V based on the "Fig 3. Typical Transfer Characteristics" seems to imply you're misinterpreting that graph (or assuming an ideal voltage source for Vds). That graph doesn't indicate that a higher Vgs will result in a higher Tj. It says that with a higher Vgs the part can sustain a higher Id (if that's what is possible from other parts of the system) and still maintain the same Tj (i.e. the curves are points where the same power will be dissipated in the junction). Feb 15, 2022 at 3:03
• While there are other considerations as to why one might want to limit Vgs to a lower value, the issue usually isn't Tj. It would be Tj, if what was supplying Vds was quite close to an ideal voltage source (i.e. nothing in the system limits the possible Id, which may or may not be the case). If Vds is truly fixed and there's nothing limiting Id, then, yes, you want to limit Vgs, as having an Rdson which is too low would result in too much current, and thus too much power being dissipated in the device. However, there's usually something else limiting Id, particularly if switching. Feb 15, 2022 at 3:03
• @Makyen Yes it reads a little confusing. I didn't mean that driving the gate harder causes an excess of temperature directly but rather that I should be mindful about the junction temperature being high. Feb 15, 2022 at 9:01

People routinely drive at 12-15V to give some margin for the bootstrap cap to discharge in high side gate drive. 20V is the rated limit of many devices though and combined with gate ringing is too close for comfort.

Your device having a max rating of 30V is unusual and on the high end. Traditionally, it has been 20V.

Big gate volts can reduce conduction losses at high currents. This can slightly reduce junction temps. One must be careful because the voltage that the semiconductor dye sees can be more than the drive volts that you have generated and measured on the scope. If you see ringing on your scope this is a warning that this could be happening and the mosfet could have a short life. If you are running high frequency with a square wave drive which is not uncommon then be mindful of gate power dissipation inside the mosfets gate spreading resistance. Sure your driver wastes more power, but gate power ratings are much much lower than total power ratings. In fact in the MHz region the nominal 10 Volts can be too high.

The manufacturer could have boasted a lower Rds(on) if they quoted at a higher Vgs.

But then you'd have to use a gate driver circuit which is able to provide that +30V Vgs in order to fulfill the manufacturer's requirements. Such gate drivers are more expensive than more common 5-15V ones, and the improvement in Rds(on) will be marginal and most likely wouldn't justify this additional cost. So, you'd rather pick a MOSFET which has an acceptable Rds(on) with a lower Vgs specified in the datasheet.

Additionally, you'll want a safety margin between the Vgs you apply to a MOSFET and the Vgs(max). Driving close to Vgs(max) will likewise mean that the voltage supply (typically a charge pump for high-side) will have to be more precise and thus more expensive, and you'll have to be very careful with ringing, because a small safety margin means even a small instability could kill the FETs.