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MH89625C-5 Datasheet(PDF) 4 Page - Mitel Networks Corporation |
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MH89625C-5 Datasheet(HTML) 4 Page - Mitel Networks Corporation |
4 / 16 page 2-272 MH89625C Preliminary Information Functional Description The Mitel MH89625C OPS SLIC (Off-Premise Subscriber Line Interface Circuit) provides a complete interface between an off-premise telephone line and an digital switching system. All BORSCHT functions are provided requiring only a few external components. The input impedance conforms with Chinese standard requirements. All functions of the SLIC are controlled by the system Drive (SD) outputs of the internal Mitel A-Law Codec MT8967. The SD outputs are controlled by the serial data input stream at CSTi. The BORSCHT Functions The MH89625C performs all of the BORSCHT functions of Battery Feed, Overvoltage Protection, Ringing, Supervision, Codec, Hybrid and Test. Battery Feed The MH89625C powers the telephone set with constant DC loop current for short lines and automatically reverts to constant voltage for long lines. The constant loop current is a function of the resistance connected from the LCA pin to VEE. Where ILoop is the desired constant loop current in mA, and R is the resistance from pin LCA to pin VEE in ohms. Overvoltage Protection The MH89625C is protected from short term (20ms) transients (+250V) between TIP and RING, TIP and ground, and RING and ground. However, additional protection circuitry may be needed depending on the requirements which must be met. Normally simple external shunt protection as shown in Figure 4 is all that is required. R (k Ω) open 348k 200k 80k 50k 30k ILoop (mA) 22.0 25.0 27.1 34.0 40.2 49.7 147.2 -ILoop (0.0001176 X ILoop) -0.002586 R = Ringing The ringing insertion circuit has the capability to provide ringing voltage to a telephone set by simply adding an external relay, ring generator and a transient protector. The internal relay driver switches ringing voltage onto the line via the external ring relay. A clamp diode is included which suppresses voltage transients during relay switching caused by the relay coil. The serial data input at CSTi controls the internal Codec’s SDo output which activates the ring driver. Refer to Table 1 for control of SLIC functions. Supervision The loop detection circuit determines whether a low enough resistance is across Tip and Ring to be recognized as an off-hook condition. When an off-hook condition occurs, the SHK and LED (the LED output can drive an LED directly) outputs toggle to a low level. These outputs also toggle with incoming dial pulses. During applied ringing (ring relay driver activated), the loop detection circuit engages a ringing filter. This filter prevents false off-hook detection due to the current associated with the AC ringing voltage as well as current transients that occur when the ringing voltage is switched in and out. The ring trip detection circuitry deactivates the ring relay driver after an off-hook condition is detected. Codec The Codec function of the SLIC is implemented using the Mitel MT8967 A-Law Codec. This device provides the conversion interface between the voiceband analog signals of a telephone subscriber loop and the digital signals required in a digital PCM (pulse code modulation) system. Eight-bit PCM encoded digital data enters and leaves the chip serially on DSTi and DSTo pins, respectively. For detailed information on the CODEC portion of the MH89625C, refer to the MT8967 integrated PCM Filer/Codec data sheet (Microelectronics Digital Communications Handbook, Mitel Semiconductor Issue 9). |
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Similar Description - MH89625C-5 |
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