CH1804 データシートの表示（PDF） - Cermetek Microelectronics

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CH1804

Family of Line Detection and Monitoring Products

Cermetek Microelectronics 

Cermetek Microelectronics, Inc.

occur in an installation, the CH1804/9 will only detect

when TIP and RING are both cut. However,

regardless of the installation wiring, the

CH1804A/CH1809A products will always detect an off-

hook condition. If it is required to detect and identify

which line (i.e., either TIP or RING) has been cut, then

a voltage sense device is required, such as the

Cermetek CH1808 line status detector product.

APPLICATION RECOMENDATIONS

Failure to Detect Cut Line. When using either the

CH1804 or the CH1809 products, external leakage

and capacitance on TIP and RING must be minimized.

Differential leakage to TIP and RING in excess of 0.1

microamperes may appear as a central office battery

voltage thereby causing the CH1804/9 to fail to detect

a cut line. Additionally, Common mode leakage to TIP

and RING in excess of 1 microampere is also

undesirable. Thus, the circuit board layout and

external wiring for TIP and RING must be well

insulated.

Off-Hook Indication Delay. Capacitance on TIP and

RING should be minimized as it could retain charge

after a transition and appear as a central office battery

voltage. This will delay detection of an Off-Hook

condition for many tens of seconds. The input

impedance of the detector circuit is approximately 10M

ohms to ground, and the 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 ten seconds.

Normal Operation. If the CH1804/A or the CH1809/A

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 minimal. 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.

Figure 2. Application Diagram indicating external

components to increase output drive, decrease

false line cut indications and provide additional

overvoltage protection.

CH1804/A and CH1809/A

Potential False Indication. The CH1804/A and

CH1809/A products reside on the telephone line and,

as such, are subject to transients produced by

electrical discharge and ring voltage transitions.

These may cause momentary false Cut Line or Off-

Hook indications. The use of additional external

capacitance on the output may be required to reduce

these false indications. The capacitance value to add

to each output should be determined by appropriate

analysis and testing for the particular application.

Cermetek recommends that the outputs be level

detected as opposed to edge detected to minimize

false indications on excessively noisy lines. Referring

to Figure 2, typical values are 0.1µf and 30K ohms for

CX and RX, respectively.

SUPPLEMENTAL PROTECTION

If the CH1804A/9A products are being used on

telephone lines that are prone to high voltage

transients, an FCC Part 15 A/B suppressor may be

required. This consists of 1.25 A fuses in both TIP and

RING lines and a 350V voltage suppressor between

TIP and RING for transient protection. A ferrite bead

inductor and 0.1µF capacitor (1500V) to ground may

also be required for EMI/RFI suppression. See

Cermetek Application Note # 126. If the CH1804A/9A

is being used with another Cermetek device where the

supplemental protection is already planned for or

available, the CH1804A/9A can share the protection if

a parallel connection to the TIP and RING pins is

made in front of the protective network.

DESIGN

CONSIDERATION

FOR

FCC

CONFORMANCE

The CH1804A/9A products include circuits that couple

to the phone line and provide FCC required isolation

and protection. The following guidelines should be

followed to maintain the conveyed FCC Part 68

registration:

1) CH1804A/9A must be mounted away from

hazardous voltages.

2) Connection of the CH1804A/9A devices to PSTN

lines should be made through a standard RJ-11C

jack or another approved connector device.

3) Circuit board traces to the CH1804A/9A TIP and

RING pins must have a spacing of greater than

0.10 inch from all adjacent traces. TIP and RING

traces should have a width of 0.020 inches.

4) TIP and RING traces should be as short as

possible to prevent coupling to other signals lines.

Mount the CH1804A/9A as close to the telephone

line connection as possible.

2003 Cermetek Microelectronics, Inc.

Page 2

Document No. 607-0015 Revision C (05/03)

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