Application Note 53
January 1993
Micropower High Side MOSFET Drivers
Tim Skovmand
Portable electronic equipment, such as notebook and
palmtop computers, portable medical instruments and
battery powered tools, are increasingly dependent upon
efficient power management to meet the challenge of
extracting more useful energy (time) from less battery
volume and weight.
One link in the power management chain which has
received increasing scrutiny, as power supply efficiencies
soar above 90%, is the logic controlled power switch.
Large sections of a typical notebook computer system, for
example, are powered via topside or “high side” MOSFET
switches. These switches can become significant sources
of power loss if not properly designed.
At first glance, P-channel MOSFETs appear to be the
natural choice for high side switching. Unfortunately, the
RDS(ON) exhibited by most P-channels is prohibitively
high. (Mother Nature has decreed that electron mobility
shall exceed hole mobility in silicon by about 2.5 times, so
that a P-channel MOSFET with the same RDS(ON) and …