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.