A power, split tailgate system is provided that allows each of an upper and a lower tailgate door to be simultaneously or independently driven between open and closed positions. Provided herein is nucleic acid encoding NT-4 useful in diagnostics and in the recombinant preparation of NT-4. The width of the resist layer in the track width direction gradually increases from the bottom to the top of the resist layer. The controller is adapted to use a sensed input voltage to determine a switching period, and is further adapted to turn the first and second power switches into an on-state at a frequency substantially corresponding to the switching period while maintaining a switching duty cycle within a predetermined range.