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MH88610
(R)
Subscriber Line Interface Circuit (SLIC) Preliminary Information
Features
* * * * * * Transformerless 2-wire to 4-wire conversion Battery and ringing feed to line Off-hook and dial pulse detection Ring ground over-current protection Loop length detection Constant current feed MH88610
ISSUE 6
April 1995
Ordering Information 20 Pin SIL Package 0C to 70C
Description Applications
Line interface for: * * * * PABX Intercoms Key Telephone Systems Control Systems The Mitel MH88610 Subscriber Line Interface Circuit provides a complete interface between a switching system and a subscriber loop. Functions provided include battery feed and ringing feed to the subscriber line, 2-Wire to 4-Wire hybrid interfacing, constant current, loop length and dial pulse detection. The device is fabricated using thick film hybrid technology in a 20-pin single in-line package.
LPGND
VBat
VDD
VEE
GNDA
TF TIP RING RF RV
Current &Voltage Sensing
2-Wire to 4-Wire Conversion
VR VX
Over Current Protection Constant Current Feed Loop Supervision
VRef LOOP SHK CAP
Figure 1 - Functional Block Diagram
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MH88610
TF LPGND VR VRef VEE GNDA LOOP VX TIP RING RF VDD IC IC RV IC NC VBat CAP SHK 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Preliminary Information
Figure 2 - Pin Connections
Pin Description
Pin # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Name TF LPGND VR VRef VEE GNDA LOOP VX TIP RING RF VDD IC IC RV IC NC VBat CAP SHK Description TF Tip Feed. Internal connection. Normally connects a pair of external diodes for protection. Loop Ground. is the system ground reference with respect to VBat. Voice Receive (input) is the 4 wire analog signal to the SLIC. Voltage Reference (Input) to set the line current feed to the subscriber line. Negative Power Supply Voltage (-5V). Analog Ground (0V). Loop Monitor Voltage (Output). is proportional to the loop length. Voice Transmit (Output) is the 4-wire analog signal from the SLIC. Connects to the "Tip" lead of the telephone line . Connects to the "Ring" lead of the telephone line. Ring Feed (Input) is normally connected to Ring relay for negative battery feed voltage and ringing voltage input. Positive Power Supply Voltage. Internal Connection. Pin cut short. Internal Connection. Pin cut short. Ring Feed Voltage connects to pin 11 (RF) through a normally closed ring relay. Internal Connection. Pin cut short. No Connection. Negative Battery Feed Supply Voltage. Connects external capacitor and resistor to ground for ring trip filter control. Switch Hook Detect (Output). Digital output of an open-collector comparator. This output will go low (VEE) when the subscriber line resistance falls below a set threshold value indicating that the telephone set has gone off-hook. This output can be monitored for dial pulse collection.
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Preliminary Information
Functional Description
The MH88610 performs a transformerless 2-wire to 4-wire conversion of the analog signal. The 2-wire circuit is the balanced line going to the subscriber loop, while the 4-wire circuit is the audio signal going to an from devices such as the voice codec or switching circuit. The SLIC also provides two status signals. switch hook (SHK) and loop length (Loop). The Loop signal is an analog voltage which is proportional to the loop length and the SHK goes low when the telephone set is off-hook.
MH88610
been detected an external circuit will deactivate the relay (K1) to disconnect the ringing voltage from pin 11 and reconnect to pin 15. At that time the SLIC will revert to constant current feed operation. For applications requiring Dial Pulse Detection the Capacitor connection to ground should be controlled such that the capacitor is only connected during ringing. During off-hook conditions (closed loop), the capacitor should be switched out. This can be performed using a transistor, relay or system drive output of a codec. Applying GNDA to the Ring Trip Filter Control pin will switch in the filter, whilst removing GNDA, (with the switch in a tristate condition), will switch out the filter. For applications using DTMF signalling, the capacitor can be permanently connected to ground.
Constant Current Feed
The MH88610 employs a complex feedback circuit to supply a constant feed current to the line. This is done by sensing the sum of the voltages across the internal feed resistors and comparing it to an input reference voltage (VRef) that determines the constant feed current. This gives the loop current as: ILoop = 25 - (VRef) mA (+2 mA) 1.25
Current Limit
The Tip or Ring may accidentally short to ground. In such a case, current will only flow through the feed resistor. This high current will be sensed and reduced by the current limit circuit to a lower value to protect the internal circuitry.
Switch Hook Detection
When the DC current exceeds an internal threshold level, the switch hook (SHK) will go low. If the loop resistance is so high that V Bat can no longer supply the required amount of loop current as determined by constant current supply circuit, the output of the switch hook (SHK) will go high impedance (open collector output) to indicate that the loop resistance is too high and the line is on hook.
Components List
R1 =Resistor 1/4w, + 5%, 30.0k R2 =Resistor 1/4w, + 5%, 750k R3 =Resistor 1/4w, + 5%, 3.9k R4 =Resistor 1/4w, + 5%, 4.7k R5 =Resistor 1/4w, + 5%, 43k R6 =Resistor 1/4w, + 5%, 470k RV1*, RV2* =Var. 160 VRMS, 250V,10J D1*, D3*, D4* =Diode Rect., 200V, 1A IN4003 D2 =Diode Rect., 200V, 1A IN4003 D5 =Diode Sw., 75V, 02A, 0.5W IN4148 Q =NPN, 2N2222 or equivalent K1 =Relay E/M, 12V, 1 form C C1*,C2*,C3*,C4*= Cap. Cer., 1.0F, 50V, 20% C5 =Cap. Elec., 1.0F, 16V 10%
Ringing And Ring Trip Detection
In Figure 3 a ringing signal (e.g., 90Vrms=+/-48Vdc) is applied to the line by disconnecting pin 15 (RV) from pin 11(RF), and connecting the ringing voltage at pin 11 (RF) by use of the relay K1. The SLIC can detect an off-hook condition during ringing but there is a large AC component which must be filtered out to give a true off-hook condition at SHK. A 1.0F capacitor connected from pin 19 (CAP) to ground will provide adequate attenuation when ringing is applied. Once an off-hook condition has
Note: Components marked * are optional for extra protection of the hybrid.
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MH88610
-5V C4
Preliminary Information
9 TIP TIP RV1
VEE
VRef 4 C3 7 +12V D5 TF VR 3 K1 Q1 20 SHK R3 CAP
RF LPGND VBat GNDA VDD
-11V
MH88610
RV2 10 RING VBat D1 D2 VBat D3 D4 15 R1 11 2 R2 1 RING VX 8 LOOP
RV
R4 R5
-+
19 R6
C5
RINGING RELAY CONTROL
VBat
18 C1 -28V
6 C2
12
-5V RING TRIP FILTER CONTROL
+5V
ILOOP = VRef mA (+2mA) 0.423
Figure 3 - Application Circuit
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Preliminary Information
Absolute Maximum Ratings*
Parameter 1 DC Supply Voltage LPGND=GNDA 2 3 Storage Temperature Package Power Dissipation Symbol VDD VEE VBat TS PD Min -15 -60 -40 100 2 Max +15
MH88610
Units V V V C W
* Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
Recommended Operating Conditions
Parameter 1 Operating Supply Voltage Sym VDD VEE VRef VBat 2 Operating Temperature TO 0
Typical figures are at 25C and are for design aid only.
Min 4.75 -5.25 -23
Typ 5.0 -5.0 -11 -28
Max 5.25 -4.75
Units V V V V
Comments
70
C
DC Electrical Characteristics
Characteristics 1 Supply Current VDD VEE 2 3 4 5 6 7 8 9 Power Consumption Constant Current Line Feed Operating Loop Resistance Off-Hook Threshold Ring Ground Over-Current protection Output High Voltage Loop (On-hook) Output High Source Current Loop (on-hook) Output Low Voltage SHK Loop (off-hook) Output Low Sink Current SHK Loop (off-hook)
- Voltages are with respect to GNDA unless otherwise stated.
Sym IDD IEE PC ILoop RLoop
Min
Typ 64 -3.4
Max 7.6 -5.0 212 1110
Units mA mA mW mW mA
Test Conditions
Standby Active VBat = -28V VBat = -28V
24 800
26 1200 33
28
42 mA
VDD-2 15 VEE 1.9 6 10 16 20
VDD
V mA
No Load RLOOP = 2.5V 10k pull-up to 5V No Load V SHK = 1.5V VLoop = 2.5V
VEE+1.5 2.4
V V mA mA
10
DC Electrical Characteristics are over recommended operating supply voltages. Typical figures are at 25C with nominal +5V supplies and are for design aid only.
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MH88610
AC Electrical Characteristics Characteristics 1 2 3 4 5 6 7 8 9 10 11 12 13 Ringing Voltage (rms) Ring Frequency Ringer Equivalence Number Ring Trip Detect time Input AC Impedance 2-wire Input Impedance at VR Output Impedance at Vx Gain 2-wire to Vx Gain VR to 2-wire 2-wire Return Loss Transhybrid Loss Longitudinal Balance Total Harmonic Distortion at Vx at Tip and Ring 14 15 16 Common Mode Rejection Ratio 2-wire to Vx Idle channel Noise (at Vx) Power supply rejection ratio VDD VDD VEE VBAT
* Typical figure are at 25C and are for design aid only.
Preliminary Information
Sym VR
Min 17
Typ*
Max 105 25 3 200
Units Vrms Hz ms k
Test Conditions
REN Zin 600 230 1 0.60 -6.75 20 THL 40 45 THD 0.1 0.1 CMRR Nc PSRR 39 37 23 23 40 0.62 -6.69
0.70 -6.65
dB dB dB dB dB
Input 6dBm at 2-wire Input 1.0V at VR 600 termination Input 0.5 V 1kHz 600 Input 0.5 V, 1kHz at V R 600 Input 0.5V, 1kHz metallic output voltage Input 6dBm at 2-wire Input 1.0V at V R Input 0.5Vrms, 1KHz at metallic output voltage C- Message at
1.0 1.0
% % dB
15
dBrnC
dB dB dB dB
At VX, ripple at Vpp, 1kHz At 2-Wire, ripple at 1Vpp, 1kHz At VX, ripple at 1Vpp, 1kHz At 2-Wire, ripple at 1Vpp, 1kHz
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Preliminary Information
MH88610
Side View
0.080 Max (2.0 Max)
2.00 + 0.020 (50.8 + 0.5)
0.52+0.02 (13.2+0.5)
1234
19 20
0.010 + 0.002 (0.25 + 0.05) 0.12 Max (3.1 Max) 0.05 + 0.01 (1.3 + 0.5) Notes: 1) Not to scale 2) Dimensions in inches). 3) (Dimensions in millimetres). * Dimensions to centre of pin & tolerance non accumulative. * 0.05 + 0.02 (1.3 + 0.05) 0.020 + 0.05 (0.51 + 0.13) * * 0.100 + 0.10 (2.54 + 0.13)
0.18 + 0.02 (4.6 + 0.5)
Figure 4 - Mechanical Data
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MH88610
Notes:
Preliminary Information
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