High-side NMOS indicates that a N-channel MOSFET will be used on the upper part of a Half, Full or H-Bridge. In other terms the source of this NMOS device is connected to the Power Rail. This approach has the distinct advantage that a N-Channel mosfet can achieve lower on resistance for the same amount of gate capacitance (and silicon area) as a comparable P-Channel device. This is true because the electron mobility of N-type channel is about 7x greater than that a similar sized P-type channel. One dominate consequence of using a high-side NMOS is that in order to turn on this device, it requires a positive Vgs, since the source is connected to the power supply, this implies that the gate needs to be driven to a voltage that is greater than the power supply voltage. This challenge is typically overcome by use of some type of boost converter, typically a charge pump or bootstrap circuit is used to provide this higher gate drive voltage for a high side NMOS.
With all of the tradeoffs considered, typically a power converter with a high-side NMOS is more area and power efficient than the equivalent high-side PMOS circuit.
Triad designs high performance power converters for a variety of applications. Our engineers intimately understand all of the tradeoffs associated with choosing to use high-side NMOS or PMOS transistors. The fabrication processes that we use also allow the flexibility to customize the FETs for a particular application and design the necessary boost circuitry to support high-side NMOS drivers.