MH88520-1 Просмотр технического описания (PDF) - Mitel Networks

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MH88520-1

German Subscriber Line Interface Circuit (SLIC)

Mitel Networks 

Preliminary Information

MH88520-1

Functional Description

The BORSH Functions

The MH88520-1 performs all of the Borsh functions

of Battery Feed Overvoltage Protection, Ringing,

Supervision and Hybrid (2-2 Wire).

Return Loss at Tip-Ring

the SLIC, and converts the ground referenced input

signal at JUNC of the SLIC into the non-balanced

output signal at Tip-Ring of the telephone line.

Mute

A logic low at the MUTE input results in muted

signals coming from Tip and Ring to the JUNC

terminal while allowing signals from the JUNC

terminal to Tip and Ring to be transmitted.

To maximise return loss, the impedance at Tip-Ring

should match the SLIC’s impedance (220R + 820R //

115nF). However, the SLIC’s input impedance is

dependent on the JUNCTOR termination resistance.

Therefore the JUNCTOR must be terminated with

754Ω.

Figure 3 illustrates a typical connection between two

SLICs through two crosspoint switches. Optimum

return loss occurs when the JUNCTOR is terminated

with 754Ω. Since the JUNCTOR input/output

impedances is 604Ω and the crosspoint switch

resistances are 75Ω + 75Ω, this configuration gives

optimum return loss as shown in Figure 4.

Hybrid

The 2-2 wire hybrid circuit converts the incoming

balanced signal at Tip and Ring of the telephone line

into a ground referenced output signal at JUNC of

Overvoltage Protection

The MH88520-1 is protected from short term (1ms)

(+250V) between Tip and Ring, Tip and Ground, and

Ring and Ground. However, additional protection

circuitry may be needed depending upon the

requirements which must be met for the final

equipment.

Loop Detection

The loop detection circuit determines whether a low

enough path is across Tip and Ring to be recognised

as an off-hook condition. (Threshold impedance =

5.4kΩ with no adjustment). This threshold level can

be adjusted by the use of external resistors as

shown in Figure 6. When an off-hook condition

occurs the SHK and LED outputs toggle to a logic

low level. These outputs also toggle during incoming

dial pulses.

TIP

RING

TIP

RING

1 MH88520-1

TIP

16

JUNC

3

RING

SLIC 1

1 MH88520-1

TIP

16

JUNC

8

RING

SLIC 2

75Ω

CROSSPOINT

SWITCH

75Ω

CROSSPOINT

SWITCH

Figure 3 - SLIC Crosspoint Switch Connection

2-65

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