MH88620IN データシートの表示（PDF） - Mitel Networks

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MH88620IN

C.O. SLIC

Mitel Networks 

MH88620IN

Preliminary Information

Tip/Ring driver circuitry such that impedance in the

feedback path gets reflected to the two wire port.

The MH88620IN’s Tip-ring impedance (Zin) is

designed to be 600Ω, when used with 25Ω PTC’s as

protection circuitry. For this requirement, Z1 and Z2

should be connected together on the PCB. To

accommodate the use of lower value PTC’s a series

resistance can be connected between Z1 and Z2.

For example, if two 8Ω PTCs are used, connect

340Ω between Z1 and Z2.

The design uses a 0.1 times impedance amplifier so

the 340Ω actually adds 34Ω of additional impedance

to the 550Ω (16 + 34 +550 = 600). For complex

impedance setting, a capacitor and/or resistor can

be connected between Z1 and Z2. For example, if

Return Loss is to be maximized for a Zin of 600

+2.2µF, a 0.22µF cap can be connected between Z1

and Z2.

Network Balance

Transhybrid loss is maximised when the line

termination impedance and SLIC network balance

are matched. The MH88620IN’s network balance

impedance can be set to Zin, or to a user selectable

value. Thus, the network balance impedance can be

set to any Indian or other international requirement.

An external Network Balance impedance is selected

which 0.1 times the impedance between N1 and

AGND. N2 to GND balances to 600 ohms.

Off-Hook and Dial Pulse Detection

The SHK pin goes low when the DC-loop current

exceeds a specified level. The threshold level is

internally set by the bias voltage of the switch-hook

detect circuitry. Dial pulses can be detected by

monitoring the interruption rate at the SHK pin.

These dial pulses would be debounced by the

system software.

Ring Trip Detection

The interface permits detection of an Off-Hook

condition during ringing. If the subscriber set goes

Off-Hook when the ringing signal has been applied,

the DC loop current flow will be detected within

approximately 100msecs and the SHK output will go

low. The Ring relay is automatically disabled by the

internal hardware.

Longitudinal Balance

The longitudinal balance specifies the degree of

common mode rejection in the 2 to 4 wire direction.

Precision laser trimming of internal resistors in the

hybrid ensures good overall longitudinal balance.

The interface circuitry can operate in the presence of

induced longitudinal currents of up to 40 mA RMS at

60 Hz.

DTMF

The DTMF tones are transmitted and received at the

4-wire port.

High voltage Capability

Inherent in the thick-film process is the ability of the

substrate to handle high voltage. The standard Mitel

thick-film process provides dielectric strengths of

greater than 1000 VAC or 1500 VDC. The thick-film

process allows easy integration of surface mount

components such as the high voltage bipolar power

transistor line drivers. This allows for simpler, less

elaborate and less expensive protection circuitry

required to handle high voltage transients and fault

conditions caused by lightning, induced voltages and

power line crossings.

On-Hook Transmission

The MH88620IN provides for on-hook transmission

which supports features such as Automatic Number

Identification (ANI). The ANI information is a FSK or

DTMF signal originating from and sent by the C.O.

during the off period of the ringing voltage being sent

to the subscriber’s set. The subscriber’s set decodes

the identification signal and displays the calling

party’s number.

Applications

As shown in the application diagram, Figure 7a, the

ringing voltage, typically 80 VRMS 25Hz biased at -48

VDC, is applied to the subscriber line through an

external relay, K1, Enabling of the relay is performed

by applying a logic high level to the relay driver

control input, RRC.

Figure 7b, shows how balanced ringing can be

accommodated if required.

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