AN804 Datasheet PDF

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 MOSFET’s drain voltage. To turn on, the n-channel MOSFET requires a positive gate-source voltage, whereas the p-channel MOSFET requires a negative gate-source potential. During switching, a MOSFET’s source voltage must remain fixed, as any variation will modulate the gate and thus adversely affect performance. Figure 1 shows this degradation by comparing n-channel and p-channel MOSFET high-side switching. N-Channel P-Channel VDD VDD VGG 0 0 Load Load VGG – Vth 0 VDD – ILrDS (1a) (1b) FIGURE 1. Comparing the Performance Between N-Channel and P-Channel Grounded-Load Switching Document Number: 70611 10-Mar-97 S FaxBack 408-970-5600 1 AN804 Vishay Sil...