Average current mode controlled converter having a buck mode, a boost mode, and a partial four-switch mode

An average current-mode controlled converter has a buck mode, a boost mode, and a four-switch mode. In one example, the converter operates in one of the three modes, depending on the difference between the converter output voltage VOUT and the converter input voltage VIN. Whether the four-switch mode is a full-time four-switch mode or a partial four-switch mode is user programmable. The novel converter can also be programmed to operate in other ways. For example, the converter can be programmed so that there is no intervening four-switch mode, but rather the converter operates either in a buck or a boost mode depending on VOUT-VIN. The converter can also be programmed so that the converter always operates in a conventional full-time four-switch mode. In one embodiment, the converter is programmed by setting an offset between two internally generated ramp signals and by setting associated limiting and inverting circuits.