The two switching regulator controllers operate 180 out of phase. This feature reduces the input ripple RMS current, thereby significantly reducing the required input capacitance. The two switching regulator outputs can also be paralleled to operate as a dual-phase regulator. The use of synchronous rectification and pulse-skip operation at light load achieves high efficiency over a wide load range. Fixed-frequency operation can be obtained by disabling the pulse-skip mode. The switching frequency of the LM2645 is user selectable between 200 kHz or 300 kHz. The first switching controller (Channel 1) features a fixed 5V output, and the second switching controller controller (Channel 2) features a fixed 3.3V output. Both channels can also be independently adjusted from 1.3 to 5.5V. The adjustable linear regulator can be adjusted from 3.3V to 15V. An internal 5V rail is also available externally for driving bootstrap circuitry. This rail also serves as the input for an internal LDO that provides the fixed 3.3V/50mA output rail. Current-mode feedback control assures excellent line and load regulation and a wide loop bandwidth for excellent response to fast load transients. Current is sensed across either the Vds of the top FET or across an external sense resistor connected in series with the drain of the top FET. Current limit is independently adjustable for each channel. The analog soft-start for the switching controllers uses an innovative new approach. It is independent of the input voltage which makes the soft-start behavior more predictable and controllable. Independant PGOOD signals monitor each of the switching regulator outputs. The switching outputs have under-voltage and over-voltage latch protection, while the output of the external linear regulator has undervoltage latch protection. The undervoltage latch can be disabled or adjustably delayed.