A method for establishing a powered link over a transmission line includes providing a constant, predetermined current to a terminal thereby causing a power transistor coupled to the terminal to conduct in a subthreshold region of transistor operation without current flowing between a drain terminal of the power transistor and a source terminal of the power transistor. The method includes estimating a size of the power transistor using a digital time signal indicative of an amount of time the constant, predetermined current is provided before a voltage level on the terminal exceeds a predetermined voltage level. In an embodiment, the predetermined voltage level is less than a threshold voltage of the power transistor.