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Electronic Telephone Line Switch
Ordering Information
Dial Pulse Pin SO-8
Breakdown Voltage Switch Resistance DP/DP
350V 18Ω Active High HT18LG
350V 18Ω Active Low HT19LG
HT18
HT19
Package Option
Features
❏ 350V breakdown voltage
❏ 18Ω maximum switch resistance
❏ Current limiting protection
❏ Operates at 2.0V input
Applications
❏ Telephone handsets
❏ Modems
❏ Fax machines
❏ Answering machines
❏ Remote meter reading
❏ Phone interface products
Absolute Maximum Ratings
V
, Input line voltage +350V
TPG
VTP, Output line voltage +18V
DP/DP continuous input voltage +10V
Storage temperature –65°C to +150°C
Junction temperature +150°C
Soldering temperature* +300°C
Power dissipation 0.8 Watt
Notes: All voltages are referenced to ground.
*Distance of 1.6mm from case for 10 seconds.
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 the off state,
they can withstand 350V on the positive input. In the on state
their series resistances are 18Ω maximum. 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).
Pin Configuration
TPG TP
HKS CS
GND DP/DP *
N/C LS
* For HT18, Pin 6 is DP.
For HT19, Pin 6 is DP.
1
2
3
4
8
7
6
5
top view
SO-8
Note: See Package Outline section for dimensions.
12/13/01
Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability
indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to
workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the
Supertex website: http://www.supertex.com. For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website.
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Electrical Characteristics
(Over operating supply voltages unless otherwise specified, TA = 0°C to +50°C)
Symbol Parameter Min Typ Max Unit Conditions
I
= 500µA, HKS, LS,
V
I
R
TPG
TPG
SW
High voltage positive supply 350 V
Input leakage current
2.0
µA
200 DP/DP = open circuit
TPG to TP switch resistance
18
TPG
DP/DP = open circuit
V
= 100V, HKS, LS,
TPG
DP/DP = open circuit
V
= 290V, HKS, LS,
TPG
V
=17V, I
TPG
TPG
HT18/HT19
=180mA, SW= On
I
TPG-ITP
I
LIM
I
HKS
ILS , I
I
DP
V
IL(HKS)
V
IH(HKS)
V
IL(LS)
V
IL(DP)
V
IH(LS)
V
IH(DP)
T
ON
T
OFF
DP
18 V
30 V
Bias current 50
100 V
I
current limiting 188 250 313 mA R
TPG
HKS input current 200 µAV
Ω
µA
=3.0V, I
TPG
=2.0V, I
TPG
V
= 5.0V, SW = On
TPG
= 10V, SW = On
TPG
= 158Ω ± 1%
EXT
= 40V to 70V
HKS
=20mA, SW= On
TPG
=5mA, SW= On
TPG
LS and DP logic input current 30 µAVLS = 3.0V, VDP = 3.0V
DP logic input current -30 µAVDP = 0V
HKS input low 0 0.2 V V
HKS input high 2.0 V
,
,
Input logic low for DP/DP and LS 0 0.2 V V
Input logic high for DP/DP and LS
1.5 10 V V
TPG
VV
Turn on time 1.0 ms V
Turn off time 1.0 ms V
= 3.0V to 70V
TPG
= 3.0V to 70V
TPG
= 3.0V to 70V
TPG
= 3.0V to 70V
TPG
= 4.5V
TPG
= 4.5V
TPG
Truth Table
HKS LS DP DP Switch State
HL or Z L or Z H or Z ON
HHL or Z H or Z ON
L or Z L or Z L or Z H or Z OFF
L or Z H L or Z H or Z ON
XXH LOFF
Z=high impedance, open circuit
X=don’t care
L=logic level low
H= logic level high
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Block Diagram
HT18/HT19
TPG TP
HKS
LS
DP
DP
(1)
(2)
(5)
(6) for HT18
(6) for HT19
H = ON
L = OFF
Charge Pump
&
Logic Control
(8)
(7)
(3)
CS
GND
Pin Description
Pin # Symb Description
1 TPG Positive input side of a telephone line, typically Tip side.
2 HKS Hookswitch input. Connect HKS to TPG to turn on the hook switch. Internally pulled low with a high value resistor.
3 GND Device ground. Negative side of a telephone line, typically Ring side.
4NCNo Connect. Open Circuit. No internal connections to the device.
5LS Line switch input. Input logic high turns on the hook switch. Internally pulled low with a high value resistor.
6DPFor HT18. Dial pulse input. Input logic high turns off the hook switch. Used for pulse dialing. Internally pulled low with a
high value resistor.
6DPFor HT19. Dial pulse input. Input logic low turns off the hook switch. Used for pulse dialing. Internally pulled high with a
high value resistor.
7CSCurrent sense input. An external resistor connected between CS and TP sets the current limit.
8TPPositive output side of a telephone line. Zener protection to prevent this output from rising above 18V is required.
Typical Application Circuit
Tip
Transient
Protection
Ring
©2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.
TPG
TP
R
SEN
HT18
HKS
or
CS
HT19
LS
DP/DP
GND
1235 Bordeaux Drive, Sunnyvale, CA 94089
3
TEL: (408) 744-0100 • FAX: (408) 222-4895
Telecom
15V
Circuit
12/13/010
www.supertex.com
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