According to one embodiment of this disclosure, an apparatus is disclosed. The apparatus includes a voltage regulator configured to produce a regulated voltage, a plurality of current circuits coupled in parallel between an output node and a power node, each of the plurality of current circuits including first and second transistors coupled in series, the first transistor of each of the plurality of current circuits being biased with the regulated voltage, and a control circuit configured to activate the second transistor of selected one or ones of the plurality of current circuits responsive, at least in part, to a voltage at the output node.