MH88600 Ver la hoja de datos (PDF) - Mitel Networks

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MH88600

0.3-15V; 4W; global SLIC. For PABX, intercoms, key systems, central office equipment

Mitel Networks 

MH88600

Preliminary Information

Functional Description

The BORSH Functions

The MH88600 performs all of the BORSH functions;

Battery Feed, Overvoltage Protection, Ringing,

Supervision and Hybrid.

Battery Feed

The MH88600 provides the loop with constant DC

current to power the telephone set. The voltage

(negative) applied at the LCA pin determines the

magnitude of the lop current.

ILoop = 3.731 x VLCA mA (±2mA)

Either the internal (VRef) or an external negative

voltage reference may be used to set the loop

current.

Overvoltage Protection

The MH88600 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

regulatory requirements which must be met.

Normally, simple external shunt protection as shown

in Figures 6,7 and 8 is all that is required.

Ringing

The MH88600 has the capability to accommodate

both balanced and unbalanced ringing sources.

Refer to Figure 7 for the Balanced Ringing Circuit

and Figure 6 for the Unbalanced Ringing Circuit.

Supervision

The MH88600 is capable of detecting both Ground

Button and Switch Hook conditions. The Ground

Button detection (a logic low at the EGB output)

operates when an imbalance in Tip and Ring DC

current exceeds an internal threshold level caused

by a grounded Ring Lead. Use of the EGB output is

restricted to the off-hook condition of the telephone.

The Switch Hook detection operates (a logic low at

the SHK output) when the DC loop current exceeds

an internal threshold level.

The Ring Trip Detection Circuit prevents false off-

hook detection due to the current associated with the

AC ringing voltage and also due to the large current

transients when the ring voltage is switched in and

out. In addition, the circuit prevents connection of the

ringing source during off-hook conditions.

Hybrid

The 2-4 Wire Hybrid circuit separates the balanced

full duplex signal at Tip and Ring of the telephone

line into receive and transmit ground referenced

signals at RX (receive) and TX (transmit) of the

SLIC. The Hybrid also prevents the input signal at

RX from appearing at TX. The degree to which the

Hybrid prevents the RX signal from appearing at TX

is specified at transhybrid loss.

Tip-Ring Drive Circuit

The audio input ground referenced signal at RX is

converted to a balanced output signal at Tip and

Ring. The output signal consists of the audio signal

superimposed on the DC Battery Feed Constant

Current. The Tip-Ring Drive Circuit is optimised for

good 2-Wire longitudinal balance.

Short Circuit Protection

The MH88600 is protected from long term (infinite)

short circuit conditions occurring between Tip and

Ring, Tip and Ground, Ring and Ground, and Ring

and Battery. The current is limited to the same value

as the Constant Current Battery Feed.

Programmable Line Impedance

The MH88600’s Tip-Ring (Zin) impedance can be

matched to the different impedances specified by

different telephone administrations worldwide. This

is accomplished by either linking specific pins as

specified in Table 1, or by adding external

components as shown in Figure 8 and Table 2.

Programmable Transmit & Receive Gain

Transmit gain (TX to Tip-Ring) and Receive Gain

(Tip-Ring to RX) can be programmed by connecting

external resistors as indicated in Figure 4 and Table

3. Alternatively, the default Receive Gain of -4d Band

Transmit Gain of +4dB can be obtained by

connecting pins as shown in figure 5 and Table3.

Note that RX is not a pin on the SLIC. The RX

terminal will be either PG4 or the connection to the

receive gain programming resistor RRX shown in

Figure 4 and Figure 5.

2-86

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