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HT0638
HT0638 Electronic Line Switch
Features
15 maximum switch resistance Current limiting protection 4 logic control inputs Operates at 2V input 2A maximum quiescent current at 100V
General Description
The Supertex HT0638 is an integrated electronic line switch controllable from four logic-level inputs. These devices are intended as a replacement for mechanical hook switches and relays in telephones, answering machines, and similar telecommunications equipment. They switch the positive (Tip) side of the telephone line using control inputs that are referenced to the negative (Ring) side of the line. In the off state, it can hold-off 375 volts. In the on state, the series resistance is 15 maximum. These devices provide adjustable current limiting via an external sense resistor. Three of the control inputs are general purpose and one is an override input that forces the switch to an off state regardless of the state of the other inputs. This override input is useful for `flash' and pulse dialing purposes. Internal pull-up/ down resistors allow the inputs to be driven from single-ended sources, push-pull sources, or left unconnected. The HT0638 is powered from the phone line and are especially useful in applications where external power is not available. Due to their low quiescent current, both of these devices exceed the on-hook resistance requirements of EIA-470-A.
Applications
Telephone handsets Fax machines Answering machines Auto-dial alarm systems
Typical Application Circuit
TPG Tip HKS LS1 LS2 DP Ring GND H = ON L = OFF CS Charge Pump & Logic Control + 15V Low Voltage Telecom IC HT0640
TP
For additional information, refer to application note AN-H32.
08/23/02
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.
HT0638
Ordering Information
Package Option Breakdown Voltage 375V Switch Resistance 15 SO-8 HT0638LG
Absolute Maximum Ratings
VTPG, Input line voltage VTP, Output line voltage HKS continuous input voltage LS1, LS2 continuous input voltage DP continuous input voltage Storage temperature Soldering temperature*
Notes: All voltages are referenced to ground. *Distance of 1.6mm from case for 10 seconds.
Typical Performance Curve
+375V +18V VTPG +20V +5V
350 300 250 ILIMIT vs. RSENSE
-65C to +150C +300C
ILIMIT (mA)
200 150 100 50 0 100 200 300 400 500 600 700 800 900 1000
RSENSE (ohms)
Block Diagram
TPG
TP
HKS LS1 LS2 DP GND H = ON L = OFF Charge Pump & Logic Control CS
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HT0638
Electrical Characteristics
(over operating supply voltages unless otherwise specified, TA = -40C to +85C)
Symbol VTPG ITPQ Parameter High voltage positive supply Input leakage current Min Typ Max 375 2.0 A 10 VTP RSW Output voltage TPG to TP switch resistance 16 18 20 15 15 30 ITPG-ITP ILIM IHKS ILS1 ILS2 IDP VIL(HKS) VIH(HKS) VIL(LS1), VIL(LS2) VIH(LS1), VIH(LS2) VIL(DP) VIH(DP) TON TOFF Bias current 50 100 ITPG current limiting HKS input current LS1 input current LS2 input current DP output current HKS input low HKS input high LS1 and LS2 input low LS1 and LS2 input high DP input low DP input high Turn on time Turn off time 0 2.0 0 1.0 0 1.0 200 300 200 136 136 500 0.2 VTPG 0.2 20 0.2 5.0 1.0 1.0 A mA A A A A V V V V V V ms ms VTPG = 4.5V VTPG = 4.5V V Unit V Conditions ITP = 10A, HKS, LS1, LS2, DP = open circuit VTPG = 100V, HKS, LS1, LS2, DP = open circuit VTPG = 375V, HKS, LS1, LS2, DP = open circuit VTPG = 50V, No Load VTPG=4.3V, ITPG=180mA, SW= On VTPG=3.0V, ITPG=20mA, SW= On, TA=0C to 50C VTPG=2.0V, ITPG=5mA, SW= On TA=0C to 50C VTPG = 5.0V, SW = On VTPG = 10V, SW = On REXT = 430 VHKS = 50V VLS1 = 3.0V, VDP = 0V VLS2 = 3.0V, VDP = 0V VDP = 0V, VHKS = 50V, VLS1=VLS2 = 3.0V
Truth Table
HKS X X H L or Z X
X = don't care L = logic level low H = logic level high
LS1 X H X L or Z X
LS2 H X X L or Z X
DP H or Z H or Z H or Z X L
Switch State ON ON ON OFF OFF
Z = high impedance, open circuit
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HT0638
Pin Configuration
TPG HKS GND LS2
1 2 3 4
8 7 6 5
TP CS DP LS1
top view SO-8
Note: See Package Outline section for dimensions.
Pin Description
TPG TP HKS LS1 LS2 DP CS GND Positive input side of a telephone line, typically Tip side. Positive output side of a telephone line. Hookswitch input. Connect HKS to TPG to turn on the electronic switch. Internally pulled low. Line switch 1 input. Positive input turns on the electronic switch. Internally pulled low. Line switch 2 input. Positive input turns on the electronic switch. Internally pulled low. Dial pulse input. A low input turns off the electronic switch. Use for pulse dialing. Internally pulled high. Current sense input. An external resistor connected between CS and TP sets the current limit. Short CS to TP if current limiting is not used. Device ground. Negative side of a telephone line, typically Ring side.
08/23/02
(c)2002 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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