ETC CH1804

The CH1804/A and CH1809/A are line status detectors that
are used to detect/monitor a device off-hook condition, or
severed, or cut telephone lines on a telephone line shared
by multiple devices. The CH1804/A is a single line monitor,
while the CH1809/A is a dual line device and can monitor
two telephone lines. The CH1804/A is a low cost subset of
the CH1809/A in the same package. The devices are used
for Alarm Systems to detect a severed telephone line. In
this mode, voltage of less than 8VDC is detected when both
lines of telephone line are cut. Or used for collision avoidance in systems where multiple telephone line access can
occur. In this mode the detector will detect any time the
telephone line voltage drops below 25VDC and can be used
for off-hook detect.
CH1804/A, CH1809/A
FCC Part 68 approved with conveyed registration
Usable on public switched telephone lines and wet
leased lines.
Detects a severed telephone cable. Does not require
Single in line package (SIP) requires minimum PCB
Low power operation. SIngle 5V operation.
1804/A, 1809/A
Detects a Cut Line
On the Local Loop
Detects Devices Offhook
Since the detector accesses the public switched telephone
lines, it must be FCC Part 68 approved. This approval is
provided with conveyed registration. A sticker is supplied
for placement on the user equipment in compliance with
FCC Part 68 requirements. The device operates on a single
5-volt supply and provides a separate active high indication
when either of the two attached lines is cut. Single in-line
package is 1.0” long and 0.5” high, requiring minimal PCB
Each device contains one or two separate independent line
detector circuits with separate Tip and Ring inputs and active high outputs for each circuit. A common 5-volt supply
provides power to both. The output of each detector circuit
has 45K ohm pull up resistance to 5 volts and 2.2 mF capacitance to ground. This is provided to filter out zero crossing pulses which can occur during ringing. This resident
source of output drive current might not be sufficient for
some applications. It is permissible to add a lower value
resistor in parallel between the output and 5 volts, if the zero
crossing pulses are not objectionable (this resistor should
not be less than 1K ohms). If more drive current is needed
while retaining zero crossing filtering, an external capacitor
must be added to keep the RC time constant, the same, or
Telephone lines may not be isolated from each other via a
common TIP line or a common RING line due to the DC
voltage supplied on the telephone system. In addition, the
ground of the telephone system may be common to the
ground of the system where the detector is installed at the
earth ground connection. If this occurs in an installation,
the CH1809/4 can only detect if TIP and RING are both cut.
However, the CH1809A/4 will always detect an off hook condition. If it is desirable to detect a single line cut from either
leg or of a given telephone line, then the logical OR of voltage and not current is required. This can be done with the
CH1808 line status detector for a single line.
Cermetek Microelectronics, Inc.
Figure 1. CH1804/A, CH1809/A Functional Block Diagram
When using each detector circuit, external leakage and capacitance on each TIp and Ring input must be minimized. Differential
leakage to Tip and Ring in excess of 0.1 microamperes can appear like a central office battery voltage to the detector circuit. Common mode leakage to Tip andRing in excess of 1 microampere is
also undesirable. Thus the circuit board layout and external wiring
for Tip and Ring must be well insulated.
Capacitance on Tip and Ring should also be minimized as it could
retain charge after a transition and appear like a central office
battery voltage for many tens of seconds or more. The input impedance of the detector circuit is approximately 10M ohms to
ground, and teh capacitance may have to be discharged for 3 or 4
time constants to indicate a detection depending on initial conditions. Thus it would be desirable to keep capacitance well below
1µF to keep the delay from exceeding tens of seconds.
If the detector is the only device on the telephone line, leakage and
differential capacitance will tend not to affect normal operation,
since the line capacitance in the central office or the local loop are
the only consideration. The more devices that share a given local
loop, such as modems and extension telephones, the greater the
capacitance and leakage possibilities. Sources of capacitance,
when on hook, include ring detection circuits in modems.
Document No. 603-0155 Rev. H (8/98)
Figure 2. Application Diagram CH1804/A, or half of a CH1809/A
Dual Cut Line Detector
The CH1804/A, CH1809/A resides on the telephone lines and as
such is subject to transients produced by electrical discharge and
ring voltage transition, which could cause momentar false cut line
indications, additional external capacitance on the output may be
desirable. The capacitance value to add to each output should be
determined by appropriate analysis and testing for particular application. It is suggested that the outputs be level detected as
opposed to edge detected to indicate a cut line. This will minimize
the possibility of false indications on excessively noisy lines. Type
reel values or .1µf or 30K ohms.
The CH1804/CH1809 detects a total drop of line voltage that is
always present when connected, whether the telephone line is offhook or on-hook. The line voltage must be at least 8V to indicate
the presence of the line. All North American public switched telephone lines and most “wet” active leased lines are suitable. “Dry”
leased lines may not be used with the CH1804/A, CH1809/A since
there is no voltage on the lines.
The CH1804/A, CH1809/A includes circuits that couple it to the
phone line and provide FCC required isolation and protection.
The following guidelines should be followed to maintain registration:
1) CH1804/A, CH1809/A must be mounted away from hazardous
2) Connecting the CH1804/A, CH1809/A to phone lines should be
made through a standard RJ11 jack or another approved connector device.
3) Circuit board traces to the Ch1804/A, CH1809/A Tip and Ring
pins must exceed 0.10 inch spacing to one another and at least
0.2 inches spacing from all other traces. Tip and Ring traces
should have normal width of 0.020 inches.
4) Tip and Ring traces should be as short as possible to prevent
coupling from othe rsignals. Mount CH1809/CH1809A close to
telephone line connection.
5) The registration label included must be affixed to the outside of
the host product.
6) For your user manual, the following information should be provided.
Cermetek Microelectronics, Inc.
If teh CH1804/A, CH1809/A is being used on telephone lines
that are prone to high voltage transient or FCC Part 15 A/B suppressor may be required. This consists of 1.25 A fuses in both
lines and a 300V stransorb for transient protector and Canadian approvals and ferrite bead inductor and 0.1 mF capacitor
(15000) to ground for EMI/RFI suppressor. See Cermetek Application Note # 126. If the 1804/A, CH1809/A is being used with
another Cermetek device where the supplemental protection is
already planned for, the CH1804/A, CH1809/A can share that
protection with parallel connector by the the Tips and RIngs in
front of the protective network.
Type of Service: The (insert your product name) is designed to
be used on standard device telephone lines. It connects to the
telephone line by means of a standard jack called the USOC
RJ-11C (or USOC FJ45S). Connection to telephone-companyprovided coin service (central office implemented systems) is
prohibited. Connection to party lines service is subject to state
Telephone Company Procedures: The goal of the telephone
company is to provide you with the best service it can. In order
to do this, it may occasionally be necessary for them to make
changes in their equipment, operations or procedures. If these
changes might affect your service or the operation of your equipment, the telephone company will give you notice, in writing, to
allow you to make any changes necessary to maintain uninterrupted service.
In certain circumstances, it may be necessary for the telephone
company to request information from you concerning the equipment, which you have connected to your telephone line. Upon
request of the telephone company, provide the FCC registration
number and the ringer equivalence number (REN); both of these
items are listed on the equipment label. The sum of aII of the
REN’s 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 useable 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, as 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.
Table 1. CH1804/A, CH1809/A Pin Description
Tip 1 - Telco 1
Ring 1 - Telco1
Out1 - Active High Output 1
Vcc - 5 Volts + 10%
Gnd - Ground
Out2 - Active High Output 2
Tip 2 - Telco 2
Ring 2 - Telco 2
Tip 1- Telco 1
Ring 1
Document No. 603-0155 Rev. H (8/98)
Table 2
CH1804/A, CH1809/A Electrical Specifications
VCC=5v + 10%
TA=0- to +55-C
Cermetek Microelectronics, Inc.
Document No. 603-0155 Rev. H (8/98)
Figure 3. CH1804/A, CH1809/A Physical Dimensions
406 TASMAN DRIVE · SUNNYVALE, CALIFORNIA 94089 · TEL: (408) 752-5000 FAX: (408) 752-5004
E-mail: [email protected]
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.
1998 Cermetek Microelectronics
Cermetek Microelectronics, Inc.
Printed in U.S.A.
Document No. 603-0155 Rev. H (8/98)