Supertex inc.

Supertex inc.

www.supertex.com

HT18

Doc.# DSFP-HT18

B031414

Features

Applications

Typical Application Circuit

Electronic Telephone

Line Switch

Tip

Ring

TPG

HKS

GND

DP

LS

CS

R

SEN

15V

TP

HT18

Telecom

Circuit

Transient

Protection

General Description

The Supertex HT18LG is an electronic line switch circuit that

replaces the mechanical hook switch contact or a discrete

hook switch in a telephone handset or modem. It switches

the positive side of the telephone line using control inputs

that are referenced to the negative side of the line. In its off

state, it can withstand 350V on the positive input. In its on

state, it has a maximum series resistance of 18Ω.

The device provides current limiting determined by an

external resistor. There are three control inputs. The HKS

pin turns on the hook switch when connected to the TPG

pin. This can be accomplished by using a mechanical switch

which closes when the handset is physically off-hook. The

LS pin allows a logic signal to turn on the hook switch. The

dial pulse, Pin 6, is used to turn the hook switch off for pulse

dialing. The dial pulse (DP) is active high.