HT18/ HT19

Features

350V breakdown voltage

18Ω maximum switch resistance

Current limiting protection

Operates at 2.3V input

Applications

Telephone handsets

Modems

Fax machines

Answering machines

Remote meter reading

Telephone interface products

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Typical Application Circuit

Electronic Telephone Line Switch

Tip

Ring

TPG

HKS

GND

DP/DP

LS

CS

15V

TP

HT18

or

HT19

Telecom

Circuit

Transient

Protection

General Description

The Supertex HT18LG and HT19LG are electronic line switch

circuits that replace the mechanical hook switch contact or a

discrete hook switch in a telephone handset or modem. They

switch the positive side of the telephone line using control

inputs that are referenced to the negative side of the line. In

their off state, they can withstand 350V on the positive input.

In their on state, they have a maximum series resistance of

18Ω.

The devices provide 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. For the HT18, the dial pulse is active high (DP),

whereas for the HT19, it is active low (DP).