The LTC1709-8/LTC1709-9 are 2-phase, VID programmable, synchronous step-down switching regulator controllers that drive two all N-channel external power MOSFET stages in a fixed frequency architecture. The 2-phase controller drives its two output stages out of phase at frequencies from 150kHz to 300kHz to minimize the RMS ripple currents in both input and output capacitors. The 2phase technique effectively multiplies the fundamental frequency by two, improving transient response while operating each channel at an optimum frequency for efficiency. Thermal design is also simplified.