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HT18 HT19
Electronic Telephone Line Switch
Ordering Information
Package Option Breakdown Voltage 350V 350V Switch Resistance 18 18 Dial Pulse Pin DP/DP Active High Active Low SO-8 HT18LG HT19LG
Features
350V breakdown voltage 18 maximum switch resistance Current limiting protection Operates at 2.0V 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 the off state, they can withstand 350V on the positive input. In the on state their series resistances are 18 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).
Applications
Telephone handsets Modems Fax machines Answering machines Remote meter reading Phone interface products
Pin Configuration Absolute Maximum Ratings
VTPG, Input line voltage VTP, Output line voltage DP/DP continuous input voltage Storage temperature Junction temperature Soldering temperature* Power dissipation
Notes: All voltages are referenced to ground. *Distance of 1.6mm from case for 10 seconds.
+350V +18V +10V -65C to +150C +150C +300C 0.8 Watt
TPG HKS GND N/C
1 2 3 4
8 7 6 5
TP CS DP/DP * LS
top view SO-8
* For HT18, Pin 6 is DP. For HT19, Pin 6 is DP. 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 1 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.
HT18/HT19
Electrical Characteristics
(Over operating supply voltages unless otherwise specified, TA = 0C to +50C)
Symbol VTPG ITPG Parameter High voltage positive supply Input leakage current Min Typ Max 350 2.0 A 200 RSW TPG to TP switch resistance 18 18 30 ITPG-ITP Bias current 50 100 ILIM IHKS ILS , IDP IDP VIL(HKS) VIH(HKS) VIL(LS), VIL(DP) VIH(LS), VIH(DP) TON TOFF ITPG current limiting HKS input current LS and DP logic input current DP logic input current HKS input low HKS input high Input logic low for DP/DP and LS Input logic high for DP/DP and LS Turn on time Turn off time 0 2.0 0 1.5 188 250 313 200 30 -30 0.2 VTPG 0.2 10 1.0 1.0 A mA A A A V V V V ms ms VTPG=17V, ITPG=180mA, SW= On VTPG=3.0V, ITPG=20mA, SW= On VTPG=2.0V, ITPG=5mA, SW= On VTPG = 5.0V, SW = On VTPG = 10V, SW = On REXT = 158 1% VHKS = 40V to 70V VLS = 3.0V, VDP = 3.0V VDP = 0V VTPG = 3.0V to 70V VTPG = 3.0V to 70V VTPG = 3.0V to 70V VTPG = 3.0V to 70V VTPG = 4.5V VTPG = 4.5V Unit V Conditions ITPG = 500A, HKS, LS, DP/DP = open circuit VTPG = 100V, HKS, LS, DP/DP = open circuit VTPG = 290V, HKS, LS, DP/DP = open circuit
Truth Table
HKS H H L or Z L or Z X
X = don't care L = logic level low H = logic level high
LS L or Z H L or Z H X
DP L or Z L or Z L or Z L or Z H
DP H or Z H or Z H or Z H or Z L
Switch State ON ON OFF ON OFF
Z = high impedance, open circuit
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HT18/HT19
Block Diagram
TPG (1) (8) TP
(2) HKS H = ON L = OFF LS DP (3) DP (6) for HT19 GND (5) (6) for HT18 (7) Charge Pump & Logic Control CS
Pin Description
Pin # Symb 1 2 3 4 5 6 6 7 8 TPG HKS GND NC LS DP DP CS TP Description Positive input side of a telephone line, typically Tip side. Hookswitch input. Connect HKS to TPG to turn on the hook switch. Internally pulled low with a high value resistor. Device ground. Negative side of a telephone line, typically Ring side. No Connect. Open Circuit. No internal connections to the device. Line switch input. Input logic high turns on the hook switch. Internally pulled low with a high value resistor. For HT18. Dial pulse input. Input logic high turns off the hook switch. Used for pulse dialing. Internally pulled low with a high value resistor. For HT19. Dial pulse input. Input logic low turns off the hook switch. Used for pulse dialing. Internally pulled high with a high value resistor. Current sense input. An external resistor connected between CS and TP sets the current limit. Positive output side of a telephone line. Zener protection to prevent this output from rising above 18V is required.
Typical Application Circuit
TPG Tip TP RSEN
Transient Protection
HKS
HT18 or HT19
CS LS
15V Telecom Circuit
Ring GND
DP/DP
12/13/010
(c)2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.
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1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: (408) 744-0100 * FAX: (408) 222-4895 www.supertex.com

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