HT0638

HT0638 HT0638 Electronic Line Switch Features ❑ 15Ω maximum switch resistance ❑ Current limiting protection ❑ 4 logic control inputs ❑ Operates at 2V input ❑ 2µA maximum quiescent current at 100V General Description 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 15Ω 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. The HT0638 is powered from the phone line and are especially useful in applications where external power is not available. Due to their low quiescent current, both of these devices exceed the on-hook resistance requirements of EIA-470-A. Applications ❑ Telephone handsets ❑ Fax machines ❑ Answering machines ❑ Auto-dial alarm systems ...