Driving and protection of high side NMOS power switches

In order to meet the driving requirements of monolithic NMOS high side switches in applications that have to work over wide supply voltage ranges (5 to 40 V), it was necessary to develop a charge pump that could generate the overdrive voltage for this supply range. A further limitation was that the operating voltage of the internal devices could not be exceeded. The author describes the design of a full wave voltage tripler charge pump, for driving high side NMOS switches, that can operate with supply voltage variations from 5 to 50 V. The power switch must also be protected from external as well as internal voltages. The protection circuits, which are necessary to ensure that the working voltage of the control devices and power switch are not exceeded, particularly when working into inductive loads and against supply line transients, are described