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MH88632B Datasheet(PDF) 4 Page - Mitel Networks Corporation |
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MH88632B Datasheet(HTML) 4 Page - Mitel Networks Corporation |
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4 / 17 page  MH88632B Preliminary Information 2-242 Functional Description The MH88632B is a Central Office Interface Circuit (COIC). It is used to correctly terminate a Central Office 2-Wire telephone line. The device provides a signalling link and a 2-4 Wire line interface between the telephone line and subscriber equipment. The subscriber equipment can include Private Branch Exchanges (PBX's), Key Telephone Systems, Terminal Equipment, Digital Loop Carriers and Wireless Local Loops. All descriptions assume that the device is connected as in the application circuit shown in Figure 3. Isolation Barrier The MH88632B provides an isolation barrier which is designed to meet FCC Part 68 (November 1987) Leakage Current Requirements. External Protection An external protection circuit may be required to assist in preventing overvoltage damage to the device and the subscriber equipment in which it is incorporated. The type of protection required is dependant on the application and the regulatory standards. Please contact the governing regulatory body and local approvals testing houses for more assistance. This protection is shown in block form in Figure 3. Suitable Markets The programmability offered by the MH88632B enhances its suitability for use throughout the world. However, care should be taken that all regulatory requirements, e.g. isolation and DC termination, are being fulfilled for the particular application in which the device is intended to be used. Line Termination When LRC is at a logic 1, LRD is taken to a logic 0 which energizes the Loop Relay (K1), connecting XLA to XLB and XLC to XLD. This places a line termination across Tip and Ring. The device can be considered to be in an off-hook state and DC loop current will flow. The line termination consists of a DC resistance and an AC impedance. When LRC is at a logic 0, the Line Termination is removed from across Tip and Ring. An internal Dummy Ringer is permanently connected across Tip and Ring which is a series AC load of (17k Ω+330nF). This represents a mechanical telephone ringer and allows ringing voltages to be sensed. This load can be considered negligible when the line has been terminated. Depending on the Network Protocol being used the line termination can seize the line for an outgoing call, terminate an incoming call, or if applied and disconnected at the correct rate can be used to generate dial pulse signals. The DC line termination circuitry provides the line with an active DC load which is equivalent to a DC resistance of between 190 Ω and 290Ω dependant on the loop current. AC Input Impedance The Input Impedance (Zin) is the AC impedance that the MH88632B places across Tip and Ring in order to terminate the telephone line. It can be user defined, set to 600 Ω or set to 900Ω. To select a 600 Ω Input Impedance, Z1 should be connected directly to Z600. No connection should be made to Z2 or Z900. To select a 900 Ω Input Impedance, Z1 should be connected directly to Z900. No connection should be made to Z2 or Z600. In order to user define the Input Impedance an impedance network should be placed between Z1 and Z2. This should be equivalent to 10 times the required Input Impedance and must be greater than 100 Ω at 3.4kHz. No connection should be made to Z600 or Z900. For example, to implement an Input Impedance of 220 Ω+(820Ω//115nF) an impedance network of 2200 Ω+(8200Ω//11.5nF) should be connected between Z1 and Z2 as shown below. Z2 Z1 2200 Ω 8200 Ω 11.5nF |
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Similar Description - MH88632B |
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