Method of setting bi-directional offset in a PWM controller using a single programming pin

摘要

A user-programmable bi-directional, constant current generator circuit allows external programming of either a positive (+) or a negative (−) polarity output current, for injection into one of two locations of the PWM controller circuit of a DC-DC voltage converter. The parameters of the DC-DC converter's offset voltage will depend upon the connection of a single programming pin to one of two programming resistors. The programming resistors are respectively referenced to different supply rail voltages (VCC and VSS). The polarity of the offset additionally depends upon where, within the PWM-controlled DC-DC converter, the programmed constant current is injected.