The Supertex HT0638 is an integrated electronic line switch controllable from four logic-level inputs. These devices are intended as a replacement for mechanical hook switches and relays in telephones, answering machines, and similar telecommunications equipment. They switch the positive (Tip) side of the telephone line using control inputs that are referenced to the negative (Ring) side of the line. In the off state, it can hold-off 375 volts. In the on state, the series resistance is 15 maximum. These devices provide adjustable current limiting via an external sense resistor. Three of the control inputs are general purpose and one is an override input that forces the switch to an off state regardless of the state of the other inputs. This override input is useful for `flash' and pulse dialing purposes. Internal pull-up/ down resistors allow the inputs to be driven from single-ended sources, push-pull sources, or left unconnected.