HT18/ HT19
Electronic Telephone Line Switch
Features
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350V breakdown voltage
18Ω maximum switch resistance
Current limiting protection
Operates at 2.3V input
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).
Applications
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Telephone handsets
Modems
Fax machines
Answering machines
Remote meter reading
Telephone interface products
Typical Application Circuit
TPG
Tip
TP
R
SEN
Transient
Protection
HKS
HT18
or
HT19
CS
15V
LS
DP/DP
Telecom
Circuit
Ring
GND
SUPERTEX [ Supertex, Inc ]
