MH88510 Просмотр технического описания (PDF) - Mitel Networks

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MH88510

Subscriber Line Interface Circuit (SLIC)

Mitel Networks 

MH88510/11

Preliminary Information

The SHK output has low drive capability while the

LED output can drive an LED directly. The detection

circuit engages a ringing filter during applied ringing.

The ringing filter ensures that the SHK output toggles

at the ringing cadence and not at the ringing

frequency. The ring trip detection circuit also

prevents false off-hook detection due to the current

associated with the AC ringing voltage as well as

current transients when the ringing votlage is

switched in and out.

Hybrid

The 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

the SLIC, and converts the ground referenced input

signal at JUNC of the SLIC into a non-balanced

output signal at Tip and Ring of the telephone line.

Return Loss at Tip-Ring

To maximise return loss, the impedance at Tip-Ring

should match the SLIC’s impedance (600Ω).

However, the SLIC’s input impedance is dependent

on the JUNC termination resistance. For a 600Ω

SLIC input impedance, the JUNC must be

terminated with 754Ω.

Figure 2 illustrates a typical connection between two

SLICs through two crosspoint switches. Optimum

return loss occurs when JUNC is terminated with

754Ω. Since the JUNC input/output is 604Ω and the

crosspoint switches resistance are 75Ω + 75Ω, this

configuration gives optimum return loss as shown in

Figure 3.

In addition, the Tip-Ring Drive Circuit has the

capability to drive a dry line (a line with no DC

current flowing); the AC Electrical Characteristics

apply (except for longitudinal balance), even when

the loop current drops to zero. Therefore, the

MH88510 has the capability to drive a line much

longer than 2000Ω providing the user is not

concerned with loop current, SHK detection or

ringing generator current.

Short Circuit Protection

The MH88510 is protected from long term (infinite)

short circuit conditions occurring between Tip and

Ring, Tip and AGND, and Ring and AGND.

Line Impedance

The MH88510’s Tip-Ring (Zin) impedance is fixed at

600Ω. For correct SLIC impedance, JUNC must be

appropriately terminated. See AC Electrical

Characteristics.

Transmit and Receive Gain

Transmit Gain (JUNC to Tip-Ring) and Receive Gain

(Tip-Ring to JUNC) are fixed. For correct gain, the

SLIC input impedance must match the line

impedance and JUNC must be appropriately

terminated.

MUTE

A logic low at the MUTE input results on, 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.

Tip-Ring Drive Circuit

The audio input ground referenced signal at JUNC is

converted to a differential output signal at Tip and

Ring. The output signal consists of the audio signal

superimposed on the DC battery feed current. The

Tip-Ring drive circuit is optimsed for good 2-Wire

longitudinal balance.

2-56

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