MT91610 데이터 시트보기 (PDF) - Mitel Networks

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MT91610

Analog Ringing SLIC

Mitel Networks 

MT91610

Preliminary Information

Meter Pulse Injection

The MT91610 provides a gain path input (ESI) for

meter pulse injection and an independent control

logic input (ESE) for turning the meter pulse signal

on and off.

Additional circuit can be used to ensure good

cancellation of meter pulse signal (Figure 4) should it

becomes audible at the 4 wire side. Usually, the

optional circuit is not required.

Gain (meter pulse) = 20 Log [0.891 * (R10 / R11)]

Components Selection

Feed Resistors

The selection of feed resistors, Ra and Rb, can

significantly affect the performance of the MT91610.

The value of 100 Ω is used for both Ra and Rb.

The resistors should have a tolerance of 1% (0.1%

matched) and a power rating of 0.5 Watt.

Calculating Components Value

There are five parameters a designer should know

before starting the component calculations. These

five parameters are:

1) characteristic impedance of the line Zo

2) network balance impedance ZNB

3) value of the feed resistors (Ra and Rb)

4) 2W to 4W transmit gain

5) 4W to 2W receive gain

The following example will outline a step by step

procedure for calculating component values. Given:

Zo = 600Ω, ZNB= 600Ω, Ra=Rb= 100Ω

Gain 2 - 4 = -6dB, Gain 4 - 2 = -1 dB

Step 1: Gain Setting (R7, R8, R9, R10)

Gain 2 - 4 = 20 Log [ R8 / R7]

-6 dB = 20 Log [R8 / R7]

∴ choose R7 = 300kΩ, R8 = 150kΩ.

Gain 4 - 2 = 20 Log [0.891 * [R10 / R9)]

-1 dB = 20 Log [0.891 * [R10/ R9)]

∴ choose R9 = 200kΩ, R10 = 200kΩ.

6

Step 2: Impedance Matching (R4, R5)

Zo / ( Ra+Rb) = kZo / R4 where kZo = R5

R5 / R4 = 3

∴ choose R4 = 100kΩ => R5 = 300kΩ

Step 3: Network Balance Impedance (R6)

Optimized Case Zo = ZNB

R6 = R7 * (R9 / R10) * 2.2446689 * ( ZNB / ZNB + Zo)

R6 = 300kΩ * (1) * 1.1223344

= 336.7kΩ

Step 4: The Loop Current (R2)

In order to remain in constant current mode during

normal operation, it is necessary that the following

equation holds:

{| I * Zt |} V < { | VBAT | - 6*VREF - 2} V

where,

I = Desirable Loop Current

Zt = Ra + Rb + maximum loop impedance

VBAT = Battery voltage

VREF= DC voltage at VREF pin

Given the parameters as follows:

Ra = Rb = 100 Ω

Expected maximum loop impedance = 1.6kΩ

(including Ra and Rb)

Desirable Loop Current = 20mA

6*Vref=8V

Then | VBAT | (min) = 1600 * 0.020 +10 = 42V

Assume that the VBAT of 42V is available, then read

the value of R2 from Figure 6, which is 50kΩ.

Step 5: Calculation Of Non-Clipping Sinusoidal

Ringing Voltage At Tip Ring (VTR)

Assume the Ringing Current is less than 40mA, the

ringing voltage (20Hz) at Tip and Ring is given as:

VTR (rms) = 0.707 * {| VBAT | + VDCRI - (15.6 *

VREF)}

VDCRI= Positive DC voltage at DCRI pin

VBAT = Negative Battery voltage

VREF= Positive DC voltage at VREF pin

AC voltage at the RV input pin is therefore

RV (rms)~= VTR (rms) / 50

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