CH1808
Telephone Line Status Detector
INTRODUCTION
FEATURES
The CH1808 Telephone Line Status Detector detects
  • FCC Part 68 approved.
    severed
    lines,
    the
    off-hook
    condition,
    remote
  • Used on public switched telephone lines and “wet”
    disconnects and incoming call ringing. This device is
    leased lines.
    ideal for security systems, alarm systems, or critical
  • Detects off-hook on the local loop.
    instrumentation products where it is essential that the
  • Detects automatic off-hook for separate telsets.
    line status be monitored.
    Because the CH1808
  • Detects a severed telephone cable; does not
    accesses the Public Switched Telephone Network
    require polling.
    (PSTN), it is FCC Part 68 approved. This approval is
  • Detects incoming ringing.
    provided to the end user with conveyed registration.
  • Optionally
    configured
    for
    remote
    off-hook
    Each unit is delivered with a label to be mounted by
    detection.
    the user on the host equipment indicating compliance
  • Requires minimum PCB area by using single in-
    with FCC Part 68 requirements.
    line package (SIP).
  • Operates at low power and uses a single +5V
    The CH1808 operates on a single 5V supply and is
    supply.
    housed in a single in-line package 1.4" long and 0.45"
    high. This package requires minimal PCB area. The
    CH1808 provides three logic outputs: Local Loop
    Monitor (LLM), Ring Indication (RI), and Off-Hook
    Detect (OHD). The LLM output becomes active when
    the CH1808 detects a loss of voltage resulting from a
    cut line or when another device goes off-hook on a
    shared line.
    The RI becomes active when the
    telephone company Central Office (CO) applies a
    ringing signal to the PSTN line. The OHD becomes
    active when current flow on the line is detected caused
    by the use of a shared handset. The OHD can also be
    used to detect a remote line disconnect event.
    PRINCIPLES OF OPERATION
    Operation of the CH1808 can be characterized by the
    following functional blocks:
    Local loop voltage loss detect
    Ring detect
    Figure 1.
    CH1808 Block Diagram.
    Off-hook/current detect
    Basic Operation. Figure 1 shows these blocks and
    All North American PSTN lines and most “wet” lease
    their input and output functions.
    The PSTN wires
    lines can use the Local Loop Voltage Loss Detect
    extending from the users equipment to the CO are
    function. “Dry” leased lines may not be used with the
    referred to as the local loop. This loop is connected to
    CH1808 because there is no voltage present. When
    the CH1808 via the TIP and RING pins.
    Drawing
    the line voltage between TIP and RING drops below
    current from the local loop signals to the CO that the
    18V, the LLM output is driven high.
    equipment is off-hook. The off-hook condition occurs
    either when answering a call or when placing a call.
    The LLM output has 45K pull-up resistance to +5V
    When not drawing current, the equipment is said to be
    and 2.2 µ F capacitance to ground. This is provided to
    on-hook.
    filter out zero crossing pulses that occur during ringing.
    If the CH1808 output drive current is not sufficient, it is
    Local loop Voltage Loss Detection. A voltage is
    permissible to add a lower value resistor (not less than
    always present whether the telephone line is in use
    1K ) in parallel between the output and the +5V pin, if
    (i.e., off-hook) or idle (i.e., on-hook). The line voltage
    the zero crossing pulses are not objectionable. If more
    must be at least 18V to indicate an operational line.
    drive current is needed while retaining zero cross
    2002 Cermetek Microelectronics, Inc.
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    Document No. 607-0012 Revision B (01/02)
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    CH1808 Telephone Line Status Detector
    filtering, an external capacitor must be added to either
    APPLICATIONS
    match the existing RC time constant or to increase it.
    The following are typical CH1808 applications.
    When using the LLM circuit, external leakage and
    Off-Hook Detect.
    The CH1808 can be used to
    capacitance on the TIP and RING input must be
    deactivate a shared line TESLET device when on off-
    minimized.
    Differential leakage in excess of 0.1 µ A
    hook condition is detected in a remote device.
    In
    may appear as a CO battery voltage to the CH1808.
    Figure 2, the CH1808 activates a relay which
    This could result in the CH1808 failing to detect a cut
    disconnects Telset 1 from the TELCO TIP line when
    line. Similarly, capacitance on the TIP and RING lines
    Telset 2 is off-hook. The relay is activated when OHD
    in excess of 0.1 µ F could delay a cut line detection for
    goes low.
    tens of seconds.
    Potential sources of capacitance
    include devices that share the local loop such as
    Ring Detection . The CH1808 may be used to create
    modems and extension telephones.
    a conditioned envelop wave form of the incoming ring
    signal. Referring to the circuitry shown in Figure 3, the
    Ring Detection. The CO signals an incoming call by
    4.7 µ F capacitor supresses the RI return to HIGH
    placing a ring signal on the local loop. The CH1808
    during zero-crossing of the ring pulse and holds RI to
    monitors the loop for this signal. The Ring Indication
    approximately 0.2V. The comparator circuit maintains
    output RI is normally HIGH.
    When the CH1808
    a stready output when RI is active. A NAND Gate may
    detects ringing, the RI output follows the ringing cycle.
    be substituted for the comparator circuit.
    It is set LOW during the 2-second (typical) ring period
    and is restored to HIGH for the 4 seconds (typical)
    Alternatively, the RI output from the CH1808 may be
    between rings.
    applied directly to a microprocessor input port and RI
    signal debouncing can be performed with software.
    False Ring Indication may occur during pulse dialing or
    Note that the RI signal frequency during ringing is
    when any device being monitored is off-hook.
    twice that of the incoming ringing signal provided by
    Therefore, RI should be ignored whenever OHD is
    the CO. The CO signal is typically 20Hz but older CO
    active or whenever pulse dialing is taking place.
    systems range from 15.3Hz to 68Hz.
    Off-Hook/Current Detection. The CH1808 supports
    a telephone handset connection via the TIP OUT and
    RING Pins.
    The CH1808 will provide a logic
    compatible indication to the host when an attached
    telephone is taken off-hook.
    The Off-Hook Detect,
    OHD, will be active LOW any time the handset is
    removed from the telephone cradle. Because pulse
    dialing is achieved by repeatedly switching the telset
    on and off-hook, the OHD will mirror this pulse by
    switching LOW and HIGH at a rate of 10 pulses per
    second (typical).
    NOISE SUPPRESSION
    The CH1808 interfaces to the PSTN line and, as such,
    is subject to transients produced by electrical
    discharge and ring voltage transitions.
    This may
    cause momentary false status change indications.
    While some suppression is built into the CH1808 and
    is adequate for most applications, additional external
    capacitance on the outputs may be required.
    Any
    added
    capacitance
    should
    be
    determined
    by
    appropriate analysis and testing in the particular
    Figure 2. Dual Telset Control.
    application. Cermetek suggests that the outputs be
    level detected as opposed to edge detected to
    minimize the false indications on excessively noisy
    lines.
    2002 Cermetek Microelectronics, Inc.
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    CH1808 Telephone Line Status Detector
    DESIGN
    CONSIDERATIONS
    FOR
    FCC
    CONFORMANCE
    The CH1808 includes interface circuits that couple to
    the PSTN line and provide FCC required isolation and
    protection.
    The following guidelines should be
    followed to maintain FCC compliance:
    1. CH1808 must be mounted away from hazardous
    voltages.
    2. Connecting the CH1808 to PSTN lines should be
    made through a standard RJ-11 jack or other
    approved connector device.
    Figure 3.
    Ring Indicator Envelope Filter.
    3. Circuit board traces to the CH1808 TIP, RING,
    and TIP OUT pins must have a spacing to
    adjacent traces exceeding 0.10 inch. TIP, RING,
    Remote Disconnect Detect.
    The Off-Hook Detect
    and TIP OUT traces should have a nominal width
    circuit may be utilized to signal when a remote call has
    of 0.020 inches.
    terminated. To use the CH1808 in this mode, connect
    the user equipment to RING and TIP OUT as shown in
    4. TIP, RING, and TIP OUT traces should be as
    Figure 4.
    short as possible to prevent coupling with other
    signals. Mount the CH1808 close to the PSTN
    During a telephone call, the OHD pin is driven LOW.
    line connection.
    Once
    the
    CO
    detects
    a
    disconnect,
    the
    CO
    intentionally removes the loop current momentarily.
    5. No additional circuitry shall be connected between
    This event can be used to signal the disconnect. The
    the CH1808 and the PSTN line’s RJ-11C jack
    loss of loop current usually occurs within 10 to 12
    except as shown in Figure 4.
    seconds of the disconnect and persists for 800 to
    1,000ms.
    The OHD output, detecting the loss of
    6. The FCC registration label included with the
    current, is driven HIGH during this event.
    CH1808 must be affixed to the outside of the host
    product.
    Figure 4.
    Disconnect Detect for Telset Unit connected to TIPOUT and RING.
    2002 Cermetek Microelectronics, Inc.
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    CH1808 Telephone Line Status Detector
    USER MANUAL
    In the event repairs are ever needed on the (insert
    The following information should be included in the
    your product name), they should be performed by
    host product user manual.
    (insert your company name) or an authorized
    representative of (insert your company name).
    For
    Type of Service : The (insert your product name) is
    information contact: (insert your company address).
    designed to be used on standard device telephone
    lines. It connects to the telephone line by means of a
    Changes in Attestation procedure for Plugs and
    standard jack called USOC RJ-11C or (USOC RJ45S).
    Jacks: (Name of applicant) attests that the network
    Connection to the telephone company provided coin
    interface plugs or jacks used on this equipment comply
    service (CO i mplemented systems) is prohibited.
    with and will continue to comply with the mechanical
    Connection to party line service is subject to state
    requirements specified in Part 68, Subpart F,
    tariffs.
    specifically the dimensions, tolerances, and metallic
    plating requirements.
    The compliance of these
    Telephone Company Procedures : The goal of the
    connectors will be assured by purchase specifications
    telephone company is to provide you with the best
    and incoming inspection.
    Documentation of such
    service it can. In order to do this, it may occasionally
    specifications and/or inspections will be provided to
    be necessary for them to make changes in their
    the FCC within 30 days of their request for same.
    equipment, operations, or procedures.
    If these
    changes affect your service or the operation of your
    equipment, the telephone company will give you
    written notice to allow you to make any changes
    necessary to maintain uninterrupted services.
    If you have any questions about your telephone line,
    such as how many pieces of equipment you can
    connect to it, the telephone company will provide this
    information upon request.
    In certain circumstances, it may be necessary for the
    telephone company to request information from you
    concerning the equipment you have connected to your
    telephone.
    Upon request by the telephone company, provide the
    FCC registration number and the ringer equivalence
    number (REN) of the equipment connected that is
    connected to your line; both of these items are listed
    on the equipment label. The sum of all the RENs on
    your telephone lines should be less than five in order
    to assure proper service from the telephone company.
    In some cases, a sum of five may not be usable on a
    given line.
    If Problems Arise : If any of your telephone equipment
    is not operating properly, you should immediately
    remove it from your telephone line because it may
    cause harm to the telephone network. If the telephone
    company notes a problem, they may temporarily
    discontinue service. When practical, they will notify
    you in advance of this disconnection.
    If advance
    notice is not feasible, you will be notified as soon as
    possible. When you are notified, you will be given the
    opportunity to correct the problem and informed of
    your right to file a complaint with the FCC.
    2002 Cermetek Microelectronics, Inc.
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    CH1808 Telephone Line Status Detector
    Table 1.
    CH1808 Pin Descriptions.
    Pin
    Name
    I/O
    Function
    1
    RING
    I/O
    Telco/Telset Port . Direct connection to the RING lead of a telset and RING lead of
    the telephone line through a standard RJ11 jack. PSTN or two-wire “wet” leased
    line connection required.
    2
    TIP
    I/O
    Telco Port . Direct connection to the TIP lead of the telephone line through a
    standard RJ11 jack. PSTN or two-wire “wet” leased line connection required.
    3
    TIP OUT
    I/O
    Telset Port . Direct connection to the TIP lead of a telset.
    4
    OHD
    O
    Off-Hook Detect . Active LOW when telset device is connected to TIPOUT and
    RING. When the telephone handset is removed from its cradle, OHD is driven
    LOW. Once active, OHD will momentarily be driven HIGH after disconnect of telset
    connected to TIPOUT and RING.
    5, 9, 10
    GND
    I
    Ground . Signal and power common ground. Pins 5, 9, and 10 are internally
    connected.
    6
    RI
    O
    Ring Indication . Active LOW. RI is driven LOW during the 2 second (typical) ring
    period and HIGH during the 4 seconds(typical) between rings.
    RI is otherwise
    HIGH (i.e., when no ring is present).
    7
    V CC
    I
    +5V: Positive Supply . This supply is +5.0VDC ± 10%.
    8
    LLM
    O
    Local Loop Monitor . Active HIGH. LLM is driven HIGH when the local loop is
    severed or when another device on the local loop is off–hook.
    Table 2.
    CH1808 Electrical Specifications.
    V CC = +5V ± 10%
    T A =0° to 55°C UNLESS OTHERWISE SPECIFIED
    Parameter
    Symbol
    Conditions
    Min.
    Typ.
    Max.
    Units
    LOGIC
    Output high
    V OH
    IOH = 40mA
    2.4
    V
    Output low
    V OL
    IOL = 1.0mA
    0.4
    V
    TELEPHONE LINE
    INTERFACE
    Line Resistance
    R L
    Tip to Ring
    7
    M
    ohms
    Input Resistance
    R I
    Tip or Ring to any other pin
    30
    1500
    M
    ohms
    Surge Protection
    Conforms to all FCC Part 68 surge,
    V
    hazardous
    voltage,
    and
    leakage
    requirements
    LLM Threshold Voltage
    V LLM
    Voltage across Tip and Ring
    16
    18
    20
    V
    LLM Detection Time
    I D
    CX = 0.001 µ F (Tip or Ring to GND)
    1
    sec
    VCX = 50V (Tip to Ring)
    OHD Threshold Current
    I D
    Current from Tip to Tip Out
    5
    10
    mA
    Loop Current
    I LOOP
    Current from Tip to Tip Out
    2
    100
    mA
    Ring Detect Threshold
    15.3 to 68Hz
    20
    130
    V rms
    Leakage Current
    I L
    Leakage to Tip to Ring
    40
    0.1
    mA
    POWER
    Leakage Current
    I CC
    Supply Voltage = +5V
    2
    5
    mA
    2002 Cermetek Microelectronics, Inc.
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    CH1808 Telephone Line Status Detector
    Table 3.
    Summary of CH1808 Family of Products.
    Model
    Summary of Features
    Operating Temperature
    CH1808
    FCC Part 68 Approved
    0°C to +70°C
    Figure 5. CH1808 Physical Dimensions and Pin Functions.
    Cermetek reserves the right to make changes in specifications at any time and without notice. The information furnished by Cermetek
    in this publication is believed to be accurate and reliable. However, no responsibility is assumed by Cermetek for its use, or for any
    infringements of patents or other rights of third parties resulting from its use. No license is granted under any patents or patent rights
    of Cermetek.
    Printed in U.S.A
    406 TASMAN DRIVE | SUNNYVALE CA 94089 | LOCAL: 408-752-5000 | TOLL FREE: 1-800-882-6271 | FAX: 408-752-5004
    WEB SITE: http:/www.cermetek.com | EMAIL: sales@cermetek.com
    2002 Cermetek Microelectronics, Inc.
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    Document No. 607-0012 Revision B (01/02)