Best MOSFET Type for H-bridge

[i_am_fubar]

So, there's a lot of MOSFET terminology that I'm a bit wooly on and I don't know how actually relevent it is to application.

Trench HEXFET
Power Trench
Enhancement
Depleation
...etc

Are there any rule of thumb application information for when to use what type?

Example, I'm building a small 5v 5A 3-phase motor driver. And am looking at the FDC8878 MOSFET.

It ticks most of the obvious boxed, 18m\$\Omega\$ RdsOn, Sub 50nS turn on/off, low nC for parasitics.

But I don't know if the Power Trench ness off it means it's good, bad or just a bit meh.

Cheers

[fcb]

Enhancement/Depletion mode are types of FET's and define how they operate: https://en.wikipedia.org/wiki/Depletion_and_enhancement_modes

Trench HEXFET, Power Trench are trademarks of corporations that in-part refer to the construction of the MOSFET: https://en.wikipedia.org/wiki/Power_MOSFET

[i_am_fubar]

So enhancment and depletion (in the case of MOSFETs) N and P type. huh, go figure it would be that easy 

[fcb]

So enhancment and depletion (in the case of MOSFETs) N and P type. huh, go figure it would be that easy 

Nope.

It's to do with whether or not the FET is 'on' or 'off' with a zero g-s voltage.

[Zero999]

So enhancment and depletion (in the case of MOSFETs) N and P type. huh, go figure it would be that easy 

Nope.

It's to do with whether or not the FET is 'on' or 'off' with a zero g-s voltage.

To complicate matters it's possible to deplete enhancement mode MOSFETs and enhance depletion mode MOSFETs. Assuming N-channel devices, applying a negative gate voltage to an enhancement mode device can often reduce the leakage current, especially with low gate threshold types and applying a positive voltage to a depletion mode device, can further reduce the on resistance.

[i_am_fubar]

  Back to the MOSFET drawing board for me

[Zero999]

Back to the MOSFET drawing board for me

Both depletion and enhancement MOSFETs work the same way. For N-type devices, increasing the gate-source voltage, increases the drain current. This is the same both for depletion and enhancement mode devices. The only difference is, in depletion mode devices, the gate voltage needs to go negative, in order to cut-off the drain current. Just think of a depletion mode device, as a MOSFET with a negative threshold voltage.

P-channel devices are the same, just with the signs of both the drain current and gate voltage reversed.

[Zero999]

A plot of a depletion and enhancement mode devices, biased to act as simple on/off switches. The gate voltages are both swept from -5V to +5V. Note how the turn on curves are similar, except the turn on voltage is negative, with the depletion mode device, yet positive with the enhancement mode device.


Full disclosure: I cheated with the depletion MOSFET, which is really a J-FET with a diode in series with the gate. I don't have a depletion mode model and couldn't be bothered finding/making one, but it'll be the same as a depletion mode MOSFET.