While controller designs boast design flexibility this typically also means increased design complexity, one aspect of this is the MOSFET selection. The choice of MOSFETs has significant impact on a controller designs’ performance and has various specifications that must be accounted for including:

• MOSFET on-state resistance or RDS(on), which dictates power loss and thermal performance
• Parasitic capacitances, which enable faster transition times and reduced switching losses
• Gate driver voltage, which Controller ICs vary in rating and determines if logic and or standard MOSFETs can be used

It takes a considerable amount of time and design effort to choose suitable Power MOSFETs. Table 5-1 is a typical table shown in data sheets that outline all the power losses that must be accounted for when selecting MOSFETs for a controller design. Converters skip this design process and have better characterizations of their performance.

Table 5-1 MOSFET Power Losses

Power Loss Mode	High-Side MOSFET	Low-Side MOSFET
MOSFET conduction
MOSFET switching		Negligible
MOSFET gate drive
MOSFET output charge		Negligible
Body diode conduction	N/A
Body diode reverse recovery