An apparatus includes a differential input pair, a first resistor, a second resistor, and a comparator. The differential input pair having first and second differential inputs. The first differential input is adapted to be coupled to an output of a controller and the second differential input is adapted to be coupled to a signal ground of the controller. The first resistor is adapted to be coupled to a third resistor via the first differential input to form a first voltage divider. The second resistor is adapted to be coupled to a fourth resistor via the second differential input to form a second voltage divider. The comparator having first and second comparator inputs. The first comparator input is coupled between the first resistor and the first differential input. The second comparator input is coupled between the second resistor and the second differential input.