1
Features
•Transformerless 2W to 4W conversion •Controls battery feed to line •Programmable line impedance
•Programmable network balance impedance •Off-hook and dial pulse detection •Ring ground over-current protection •Programmable gain
•Programmable constant current feed •
-22V to -72V battery operation
Applications
Line interface for:•PABX/ONS •Intercoms
•Key Telephone Systems •
Control Systems
Description
The Mitel MT91600 provides an interface between a switching system and a subscriber loop, mainly for short loop SLIC applications. The functions provided by the MT91600 include battery feed, programmable constant current, 2W to 4W conversion, off-hook and dial pulse detection, user definable line and network balance impedance’s and the capability of programming the audio gain externally. The device is fabricated as a CMOS circuit in a 28 pin SSOP package.
Figure 1 - Functional Block Diagram
TD
RING Tip Drive Controller胡风反党集团
Audio Gain & Network Balance Circuit
2 W to 4 W Conversion & Line Impedance
Relay Driver
Line Sense
Over-Current Protection Circuit
Ring Drive Controller
Loop Supervision
TIP TF RF C3A C3B RV RD
VR
Z3Z2Z1RL YC RL YD
VEE
GND VDD C2B C2A C1SHK VREF IC X3X2X1
VX DS5057
ISSUE 7
August 1999
Package Information
MT91600
28 Pin SSOP Package -40°C to +85°C
MT91600
Programmable SLIC Preliminary Information
司马义艾买提
MT91600
Preliminary Information
2
Figure 2 - Pin Connections
Pin Description
Pin #Name Description
1VDD Positive supply rail, +5V .
2TD Tip Drive (Output). Controls the Tip transistor.
3TF Tip Feed.Connects to the Tip transistor and to the TIP lead via the Tip feed resistor.4TIP Tip.Connects to the TIP lead of the telephone line.5RING Ring.Connects to the RING lead of the telephone line.
6
VREF
Reference Voltage (Input). This pin is used to set the subscribers loop constant current. Changing the input voltage sets the current to any desired value within the working limits. VREF is related to VLC.
7IC Internal Connection (Input). This pin must be connected to GND for normal operation.8RF Ring Feed.Connects to the RING lead via the Ring feed resistor.
9RV Ring Voltage and Audio Feed.Connects directly to the Ring drive transistor and also to Ring Feed via a relay.
10RD Ring Drive (Output).Controls the Ring transistor.
11C3A A filter capacitor for over-current protection is connected between this pin and GND.12C3B A filter capacitor for over-current protection is connected between this pin and GND.13C2B A capacitor for loop current stability is connected between this pin and C2A.14C2A A capacitor for loop current stability is connected between this pin and C2B.
15Z1Line Impedance Node 1. A resistor of scaled value "k" is connected between Z1 and Z2. This connection can not be left open circuit.
16Z2Line Impedance Node 2. This is the common connection node between Z1 and Z3.17Z3Line Impedance Node 3. A network either resistive or complex of scaled value "k" is connected between Z3 and Z2. This connection can not be left open circuit.18X1Gain Node 1. This is the common node between Z3 and VX where resistors are connected to set the 2W to 4W gain.
19VX Transmit Audio (Output). This is the 4W analog signal to the SLIC.
20X3Gain Node 3. This is the common node between VR and the audio input from the CODEC or switching network where resistors are fitted to sets the 4W to 2W gain 21
VR
Receive Audio (Input). This is the 4W analog signal to the SLIC.
Z3X3VREF
RLYD VEE RF GND Z2IC RING TIP RV 12345678910111213142827262524232221201918171615
TF VDD TD RD C3A C3B C2B C2A RLYC SHK C1X2VR VX X1Z1
元器件交易网b2b
Preliminary Information
MT91600
3
22X2Gain Node 2.Networks, either resistive or complex, are connected between this node,VR and GND to set the Network Balance Impedance for the SLIC.23C1 A filter capacitor for ring trip is connected between this pin and GND.
24SHK Switch Hook (Output).This pin indicates the line state of the subscribers telephone.The output can also be used for dial pulse monitoring. SHK is high in off-hook state.25RL YC Relay Control (Input).An active high on this pin will switch RL YD low.
26RL YD Inverted Output of RLYC.It is used to drive the bipolar transistor that drives the relay (see Figure 5.)
27GND Ground. Return path for +5V and -5V.This should also be connected back to the return path for the loop battery, LGND and relay drive ground RL YGND.28
VEE
Negative supply rail, -5V .
Pin Description (continued)
Pin #Name Description
Functional Description
The MT91600 is the analog SLIC for use in a 4 Wire switched system. The SLIC performs all of the normal interface functions between the CODEC or switching system and the analog telephone line such as 2W to 4W conversion, constant current feed,ringing and ring trip detection, current limiting, switch hook indication and line and network balance impedance setting using minimal external components.
Refer to Figure 5 for MT91600 components designation.
2 Wire to 4 Wire Conversion
The hybrid performs 2 wire to 4 wire conversion by taking the 4 wire signal from an analog switch or voice CODEC, a.c. coupled to V R , and converting it to a 2 wire differential signal at tip and ring. The 2wire signal applied to tip and ring by the telephone is converted to a 4 wire signal, a.c. coupled to Vx which is the output from the SLIC to the analog switch or voice CODEC.
Gain Control
It is possible to set the Transmit and Receive gains by the selection of the appropriate external components.
The gains can be calculated by the formulae:2W to 4W gain:
Gain 2 - 4 = 20*Log [ R13 / R12]
4W to 2W gain:
Gain 4 - 2 = 20*Log [0.891 * (R14 / R15)]
Impedance Programming
The MT91600 allows the designer to set the device’s impedance across TIP and RING, (Z TR ), and network balance impedance, (Z NB ), separately with external low cost components.
For a resistive load, the impedance (Z TR ) is set by R11 and R18. For a complex load, the impedance (Z TR ) is set by R11, R18, R19 & C8 (see Figure 5.)The network balance, (Z NB ), is set by R16, R17 & C3(see Figure 5.)
The network balance impedance should be calculated once the 2W - 4W gain has been set.
Line Impedance
For optimum performance, the characteristic impedance of the line, (Z o ), and the device’s impedance across TIP and RING, (Z TR ), should match. Therefore:Z o = Z TR
The relationship between Z o and the components that set Z TR is given by the formula:Z o / ( R1+R2) = kZ o / R11where kZ o =Z LZ
Z LZ = R18, for a resistive load.
Z LZ = [R18 + (R19 // C8)], for a complex load.
元器件交易网b2b
MT91600
Preliminary Information
4
金元外交The value of k can be set by the designer to be any value between 20 and 250. Three rules to ensure the correct operation of the circuit:(A) R18 + R19 > 50k Ω(B) R1 = R2.
(C) R11 > =50k Ω
It is advisable to place these components as close as possible to the SLIC.
Network Balance Impedance
The network balance impedance, (Z NB ), will set the transhybrid loss performance for the circuit. The balance of the circuit is independent of the 4 - 2 Wire gain but is a function of the 2 - 4 Wire gain.
The method of setting the values for R16 and R17 is given by the formula:
R17=[1.782 * Z o / ( Z o +Z NB ) * ( R13 / R12 )]R17 + R16[1 + R13 / R12]where Z NB is the network balance impedance of the SLIC and Z o is the line impedance.(R16 + R17) >= 50k Ω
It is advisable to place these components as close as possible to the SLIC.
Loop Supervision & Dial Pulse Detection
The Loop Supervision circuit monitors the state of the phone line and when the phone goes "Off Hoo
k"the SHK pin goes high to indicate this state. This pin reverts to a low state when the phone goes back "On Hook" or if the loop resistance is too high for the circuit to continue to support a constant current.The SHK output can also be monitored for dialing information when used in a dial pulse system.
Constant Current Control
The SLIC employs a feedback circuit to supply a constant feed current to the line. This is done by sensing the sum of the voltages across the feed resistors, R1 and R2, and comparing it to the input reference voltage, Vref, that determines the constant current feed current.
The MT91600’s programmable current range is between 18mA to 32mA.
Line Drivers & Overcurrent Protection
The Line Drivers control the external Battery Feed circuit which provide power to the line and allows bi-directional audio transmission.
The loop supervision circuitry provides bias to the line drivers to feed a constant current while the over-current protection circuitry prevents the ring driver from causing the ring transistor to overload.
The line impedance presented by the Line Driver circuitry is determined by the external network,which may be purely resistive or complex, allowing the circuit to be configured for use in any application.The impedance can also be fixed to one value and modified to look like a different value by reflecting an impedance through the SLIC from an intelligent CODEC or DSP module.
There is long term protection on the RING output against accidental short circuits that may be applied either across TIP/RING to GND or RING to GND.This high current will be sensed and limited to a value that will protect the circuit.
In situations where an accidental short circuit occurs either across TIP/RING to GND or RING to GND, an excessive amount of current will flow through the ring drive transistor, Q3. Although the MT91600 will sense this high current and limit it, if the power rating of Q3 is not high enough, it may suffer permanent damage. In this case, a power sharing resistor, R23,can be inserted (see Figure 5) to dissipate some of the power. Capacitor C13 is inserted to provide ground point. The criteria for selecting a value for the power sharing resistor R23 can be found in the application section of this datasheet.
Ringing and Ring Trip Detection
Ringing is applied to the line by disconnecting pin 8,RF , from pin 9, RV, and connecting it to a ringing source which is battery backed. This may be done by use of an electro-mechanical relay. The SLIC is capable of detecing an Off Hook condition during ringing by filtering out the large A.C. component by use of the external components connected to pin 23.This filter allows an Off Hook condition to be monitored at SHK, pin 24.
元器件交易网b2b
Preliminary Information
MT91600
5
When using DTMF signalling pulse dialling is not used, the capacitor, C7, can be permanently connected to ground and does not require to be switched out during dialling.
Power up Sequence
The circuit should be powered up in the following order: AGND, VEE, VDD, V BAT.
Application
The following Application section is intended to demonstrate to the user the methods used in calculating and selecting the external programming components in implementing the MT91600 as an analog line interface in a communication system.The programming component values calculated below results in the optimum performance of the device.
Refer to Figure 5 for MT91600 components designation.
Component Selection
Feed Resistors (R1, R2)
The selection of feed resistors, R1 and R2, can significantly affect the performance of the MT91600.It is recommended that their values fall in the range of:
200Ω <= R1 <= 250Ω
where, R1 = R2
The resistors should have a tolerance of 1% (0.15%matched) and a power rating of 1 Watt.Loop Current Setting (R3, R4, C9)
By using a resistive divider network, (Figure 3), it is possible to maintain the required voltage at Vref to set I LOOP . The loop current programming is based on the following relationship:
I LOOP = -[ F * V LC + G * V BAT ] * K o * H (R1 +R2)where,
F = R4 / (R4 + R3)
G = R3 / (R4 +R3)
K o = 200000 / (200000 + (R4//R3) )H = 1.07
I LOOP is in Ampere
From Figure 3 with R1 = R2 = 220ΩFor I LOOP = 25mA, V LC = 0V, Vbat=-48V
Figure 3 - Resistor Divider
C9 is inserted to ensure pin 6, Vref, remains und. 100nF is recommended.
邓恩桉
I LOOP can also be set by directly driving Vref with a low impedance voltage source. (See Figure 4). It is recommended that a small resistor be placed in series with the Vref pin. In this case:I LOOP = 1.07 * Vs
where, Vs < 0
(R1 +R2)
Figure 4 - Direct Voltage
Calculating Component Values For AC Transmission
There are five parameters a designer should know before starting the component calculations. These five parameters are:
1) characteristic impedance of the line Z o 2) network balance impedance Z NB
3) value of the feed resistors (R1 and R2)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:
R343k Ω
V LC
V REF
6
MT91600
R4130k Ω
V BAT
C9 100nF
2k Ω
V REF
6
MT91600
C9 100nF
Vs
元器件交易网b2b
MT91600Preliminary Information
6Z o = 600Ω, Z NB= 600Ω, R1=R2= 220ΩGain 2 - 4 = -1dB, Gain 4 - 2 = -1dB
Step 1: Gain Setting (R12, R13, R14, R15)
Gain 2 - 4 = 20 Log [ R13 / R12]
-1 dB =20 Log [R13 / R12]
∴ R12 = 112.2kΩ, R13 = 100kΩ.
Gain 4 - 2 = 20 Log [0.891 * [R14 / R15)]
-
1 dB = 20 Log [0.891 * [R14 / R15)]
∴ R14 = 100kΩ, R15 = 100kΩ.
Step 2: Impedance Matching (R11, R18, R19, C8)
a) Z o / ( R1+R2) = kZ o / R11
600/(220+220) = (k*600)/R11
let k = 125
∴ R11 = 55kΩ.
b) In general,
kZ o=Z LZ
where:
Z LZ = R18, for a resistive load.
Z LZ = [R18 + (R19 // C8)], for a complex load.
Since we are dealing with a resistive load in this example Z LZ = R18, and therefore:
kZ o = R18
(125 * 600)= R18
∴ R18 = 75kΩ.
Step 3: Network Balance Impedance (R16, R17)
R17=[1.782 * Z o/ ( Z o+Z NB) * ( R13 / R12 )] R17 + R16[1 + R13 / R12)]
R17= 0.4199
R17 + R16
set R17 = 100kΩ, R16 becomes 138kΩ.
∴ R16 = 138kΩ, R17 = 100kΩ.
Complex Line Impedance, Z o
In situations where the characteristic impedance of the line Z o is a complex value, determining the component values for impedance matching (R11, R18, R19, C8) is as follows:Given Z o = 220Ω + (820Ω // 120nF)
Z o / ( R1+R2) = kZ o / R11 (Equation 1)
where, kZ o = [R18 + (R19 // C8)]
Choose a standard value for C8 to find a suitable value for k.
Since 1nF exists, let C8 = 1nF then,
济南铁路局
k = 120nF / C8
k = 120nF / 1nF
∴k =120
R18 = k * 220Ω
R18 = 120 * 220Ω
R18 = 26400
R19 = k * 820Ω
R19 = 120 * 820
R19 = 98400
∴ R18 = 26k4Ω, R19 = 98k4Ω
From (Equation 1)
R11 = k * (R1 + R2)
R11 = 120 * (220Ω + 220Ω)
∴ R11 = 52k8Ω
Power Sharing Resistor (R23)
To determine the value of R23, use the following equations:
R23(max)= |Vbat(min)| - 100 - (2*R2 + Lr + DCRP) 30mA
R23(min)= |Vbat(max)| -Pd(max) - R2
40mA 1.6mA
where,
Vbat(min/max) = the expected variation of Vbat.
R2 = the feed resistor.
Lr = maximum DC loop resistance.
DCRP = DC resistance of the phone set.
林荫道
Pd(max) = the maximum power dissipation of the ring drive transistor Q3.
If R23(max) > R23(min), then set R23 to be the geometric center:
R23 = Square Root (R23(max) * R23(min))
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