AN804

AN804 Vishay Siliconix P-Channel MOSFETs, the Best Choice for High-Side Switching Historically, p-channel FETs were not considered as useful as their n-channel counterparts. The higher resistivity of p-type silicon, resulting from its lower carrier mobility, put it at a disadvantage compared to n-type silicon. Getting n-type performance out of p-type FETs has meant larger area geometries with correspondingly higher inter-electrode capacitances. Consequently, a truly complementary pair—a p-channel and an n-channel device that match in all parameters—is impossible. Yet, despite its shortcomings, the p-channel MOSFET performs a vital “high-side” switch task that the n-channel simply cannot equal. Used as a high-side switch, a p-channel MOSFET in a totem-pole arrangement with an n-channel MOSFET will simulate a high-current, high-power CMOS (complementary MOS) arrangement. Although the p-channel MOSFET cannot complement the n-channel in both on-resistance and capacitance simultaneously, such combinations as the low-threshold p-channel TP0610 and the n-channel 2N7000 together offer outstanding performance as a complementary pair. CIRCUIT APPLICATIONS Switching Ground-Return Loads The principal application of the p-channel, enhancementmode MOSPOWER FET is in switching power (or voltage) to grounded (ground return) loads. To drive the FET properly, the gate voltage must be referenced to its source. For enhancement-mode MOSFETs, this gate potential is of the same polarity as the ...