Voltage regulators, such as DC to DC converters, are used to provide stable voltage sources for electronic systems. Efficient DC to DC converters are particularly needed for battery management in low power devices, such as laptop notebooks and cellular phones. Switching voltage regulators (or simply “switching regulators”) are known to be efficient DC to DC converters. A switching regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and filtering the high frequency input voltage to generate the output DC voltage. Specifically, the switching regulator includes a switch for alternately coupling and decoupling an input DC voltage source, such as a battery, to a load, such as an integrated circuit. An output filter, typically including an inductor and a capacitor, is coupled between the input voltage source and the load to filter the output of the switch and thus provide the output DC voltage. A controller, such as a pulse width modulator or a pulse frequency modulator, controls the switch to maintain a substantially constant output DC voltage.
Laterally diffused metal oxide semiconductor (LDMOS) transistors are used in switching regulators as a result of their low specific on-resistance and high drain to source breakdown voltage. The high breakdown voltage in such devices is achieved by having a sufficiently long drift region between the gate and the drain. A long drift region, on the other hand, increases the resistance between the gate and the drain, thereby reducing the drain current. A long drift region also results in an increased cell pitch.
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