a switching regulator that has first , second , third and fourth terminals , a first power transistor disposed between the first terminal and a first node , a second power transistor disposed between the first node and a second node , a filter including a capacitor and an inductor , and a controller . the first power transistor is partitioned into a plurality of individually - addressable first transistor segments . the second node couples the second and fourth terminals . the second power transistor is partitioned into a plurality of individually - addressable second transistor segments . the inductor is disposed between the first node and the third terminal , and the capacitor is disposed between the third and fourth terminals . the controller is operable in a plurality of modes including a normal mode in which the controller opens and closes all of the first transistor segments and all of the second transistor segments , and a test mode in which the controller opens and closes less than all of the first transistor segments and all of the second transistor segments .