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MH88422
Line Interface Circuit Preliminary Information
Features
* * * * * * * * * * * * FAX and Modem interface (V29/V22 bis) Variants match German, UK & 600 network impedances Provides reinforced barrier to international PTT requirements Transformerless 2-4 Wire conversion Loop start operation Pulse and DTMF operation Accommodates external monitor phone Line state detection outputs: -loop current/ringing outputs Single +5V operation, low idle power (5mW) Full Duplex Suitable for power down applications MH88422-1 MH88422-2 MH88422-3
ISSUE 5
April 1995
Ordering Information 14 Pin DIL Package 14 Pin DIL Package 14 Pin DIL Package
Surface Mount Options are available by adding the Suffix "S"
Description
The Mitel MH88422 Line Interface Circuit provides a complete audio and signalling link between audio equipment and central office. The functions provided by the MH88422 include 2-4 Wire conversion, loop seizure, ring voltage and loop current detection. The device is fabricated as thick film hybrid which incorporates various technologies for optimum circuit design, high voltage isolation and very high reliability. Variants are provided to meet German (-1) and UK (-3) line impedance (see section on Line Impedances), as well as a 600 variants (-2).
Applications
Interface to Central Office for: * DAA * * * * Modem FAX Answering Machine Terminal Equipment
Isolation Barrier
Power Supply OptoIsolation OptoIsolation TXIN TF RLS Input Buffer OptoIsolation Ring & Loop Buffer USER CONNECTIONS Audio Input Buffer OptoIsolation
VDD AGND
TIP RING
Active Termination
Logic Input Buffer Audio Buffer Transhybrid Loss Cancellation Circuit
LC
VR
Audio Buffer
VX
RVLC
NETWORK CONNECTIONS
Figure 1 - Functional Block Diagram
2-21
MH88422
Preliminary Information
VDD AGND LC RVLC NC VX VR
1 2 3 4 5 6 7
14 13 12 11 10 9 8
TIP RLS NC TF TXIN RING NC
Figure 2 - Pin Connections
Pin Description
Pin # 1 2 3 4 Name VDD AGND LC RVLC Description Positive Power Supply Voltage. +5V. Analog Ground. 4-Wire Ground. Normally connected to System Ground. Loop Control (Input). A logic low activates internal circuitry which provides a dc termination across Tip and Ring. Used for seizing the line and dial pulsing. Ring Voltage and Current Detect (Output). A logic low indicates that loop current is detected. The loop current can be due to the external monitor phone or the MH88422 in the off-hook mode. The RVLC output pulses when the external monitor phone is dial pulsing or when the MH88422 is dial pulsing via the LC input. In addition, when the MH88422 is on the on-hook mode, a pulsing output indicates ringing voltage across the Tip and Ring leads. The pulsing output frequency is twice the ringing frequency. No Connection should be made to this pin. Transmit (Output). 4-Wire ground (AGND) referenced audio output, biased at 2.5V. Outputs in off-hook mode only. Receive (Input). 4-Wire ground (AGND) referenced audio input, biased at 2.5V. LC must be activated low and loop current must be flowing. No Connection should be made to this pin. Ring Lead. Connects to the "Ring" lead of the central office through an optional relay contact. The central office "Tip" and "Ring" leads may be interchanged. Transmit (Input). Connects to the "Ring" lead of the central office through a coupling capacitor. Tip Feed. Connects to the "Tip" lead of the central office through an internal resistor and an optional external resistor. No Connection should be made to this pin. Ring Loop Sense (Input). Sense node for ringing voltage detector and the loop current detector. Tip Lead. Connects to the "Tip" lead of the central office through an optional relay contact. The central office "Tip" and "Ring" leads may be interchanged.
5 6 7 8 9 10 11 12 13 14
NC VX VR NC RING TXIN TF NC RLS TIP
2-22
Preliminary Information
Functional Description
The MH88422 Line Interface Circuit is a COIC (Central Office Interface Circuit) used to interface FAX's Modems or user defined equipment to Central Office 2-Wire Analog Trunks.
MH88422
The RVLC outputs pulses when the external monitor phone is dial pulsing or when the MH88422 is dial pulsing via the LC mode. In addition, when the MH88422 is on-hook, a pulsing output indicates that ringing voltage is across the tip and ring leads; the pulsing output frequency is twice the ringing frequency. See Figure 3. Ringing frequency may require external validation. An RC monostable is usually satisfactory for this purpose or this may also be achieved using software applications.
Opto-Isolation
The isolation barrier is designed to meet regulatory requirements for a reinforced barrier of 3kVac. It provides full isolation of mains voltages up to 250V RMS and all telecom voltages. In order that this barrier is not bypassed a creepage/ clearance distance of 6.4mm minimum must be maintained between wiring, pcb tracking, etc., connected to external circuitry on either side of the barrier. To make this requirement simpler, pins on the MH88422 connected to opposite sides of the barrier are on opposite sides of the package.
2-4 Wire Conversion
The 2-4 Wire conversion circuit converts the balanced full duplex signal at Tip and Ring of the central office line into a transmit ground referenced signal at VX (Transmit) of the MH88422. It also converts the receive ground referenced signal at VR (Receive) of the MH88422 into a balanced transmit signal at Tip and Ring of the central office line. In full duplex transmission, the Tip-Ring signal consists of an audio signal from the central office as well as an audio signal due to the VR input. There is an internal cancellation circuit which prevents the VR signal appearing at the VX output. The degree to which the 2-4 wire conversion circuit minimizes the contribution of the VR signal at the VX output is specified as transhybrid loss (THL). The MH88422 is suitable to drive a COMBO II codec or a VLSI modem device.
External Protection Circuit
To meet regulatory high voltage requirement, an external protection circuit is required. The protection circuit shown in Figure 3 (Clamp Diode D1) is recommended.
DC Loop Termination
The DC loop termination circuitry provides the loop with an active DC load termination when a logic low is applied to the LC (Loop Control) input. The termination is similar to a resistance of approximately 300 (loop current dependent). Internal optically isolated circuitry is used to switch the termination in and out the loop. This is used for both seizing the line as well as generating dial pulses. The MH88422 will not seize the line when powered down.
Line Impedance
The MH88422 provides a fixed Tip-ring impedance which conforms to the following PTT requirements. MH88422-1 Zin = 200 + 820 // 115nF Germany MH88422-2 Zin = 600
Supervision Features
The supervision circuitry is capable of detecting ringing voltage and loop current as well as the status of an optional external monitor phone. The RVLC (Ring Voltage Loop Current Detect) output provides a logic low when loop current flows due to the external monitor phone or the MH88422 being in the off-hook mode.
MH88422-3 Zin = 370 + 620 // 310nF UK
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MH88422
Preliminary Information
.
Absolute Maximum Ratings* - All voltages are with respect to AGND unless otherwise specified.
Parameter 1 2 3 4 5 DC Supply Voltage Storage Temperature DC Loop Voltage Ringing Voltage Loop Current Symbol VDD TS VBat VR ILoop Min -0.3 -55 -100 Max 6 +80 +100 120 90 Units V C V VRMS
mA
* Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied
Recommended Operating Conditions.
Parameters 1 2 3 DC Supply Voltages Operating Temperature Ringing Voltage Sym VDD TOP VR Min 4.5 0 75 Typ 5.0 Max 5.5 70 Units V C VRMS VBat=-48V Test Conditions
Typical figures are at 25C with nominal +5V supply and are for design aid only
Loop Electrical Characteristics*
Characteristics
1
Sym VR
Min 27
Typ
Max 20 7
Units VRMS VRMS VRMS VRMS Hz
Test Conditions Refer to FT2 1TR2 for test method Externally Adjustable
Ringing Voltage -1 Variant only Ringing Voltage All other Variants
No Detect Detect No Detect Detect
VR 14 15 40k 15
2 3 4 5 6
Ringing Frequency On-Hook 2-wire Impedance Operating Loop Current Operating Loop Resistance Off-Hook DC Voltage -1 Variant -2 Variant -3 Variant
68
1kHz
80 2800
mA V V V V V V A A VBat=-48V, ILoop=15mA ILoop=25mA ILoop=42mA ILoop=15-20mA ILoop=26mA ILoop=25mA ILoop=42mA 100VDC VBat=-50V
6.0 6.0 4.0 4.0 6.0 6.0
9.6 15 6.0 7.8 9.0 12.5 10 9 10
7 8 9 10
Leakage Current (2-Wire to AGND) Leakage Current on Hook (Tip to Ring) DC Resistance during dialling -1 variant only Dial Pulse Distortion -1 Variant All other Variant ON OFF 0 +6 0
200 +2 +8 +2
220 +4 +10 +4
ms ms ms
ILoop=20-40mA
* Loop Electrical Characteristics are over recommended operating conditions unless otherwise stated. Typical figures are at 25C and are for design aid only. Note 1: All of the above characteristics use a test circuit as per Figure 3.
2-24
Preliminary Information
DC Electrical Characteristics
Characteristics 1 2 3 4 5
RVLC LC
MH88422
Sym IDD PC VOL VOH VIL VIH IIH IIL
Min
Typ 3 15
Max
Units mA mW
Test Conditions VDD = -5.0V, Idle state VDD = -5.0V, Idle state IOL = 4mA IOH = 0.4mA
Supply Current Power Consumption Low Level Output Voltage High Level Output Voltage Low Level Input Voltage High Level Input Voltage Low Level Input Current High Level Input Current
0.4 2.4 0.8 2.0 60 60
V V V V A
VIH = 5.0V VIL = 0.0V
DC Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. Typical figures are at 25C with nominal+ 5V supplies and are for design aid only.
AC Electrical Characteristics - MH88422 All Variants
Characteristics 1 2 3 4 Input Impedance VR Output Impedance at VX Receive Gain (VR to 2-wire) Sym Min Typ 47k 10 3.5 0 0 Max Units dB dB dB Input 0.5V at 1kHz 300 Hz 3400 Hz THD <5% @ 1kHz ILoop =15 to 40mA +2.0 +2.0 THD at 2-wire at VX 7 Power Supply Reject Ratio at 2-wire at VX Transhybrid Loss PSRR 30 30 THL 20 dB dB dB 1.2 1.2 % % +3.0 +3.0 dBm dBm Input -10dB at 1kHz DC loop = 25mA VDD=5.0V Ripple 0.1V,1kHz on VDD Input -3.5dBm, 1kHz at VR VDD=4.5V to 5.5V Test Conditions
Frequency Response Gain (relative to Gain @ 1kHz) Signal Output Overload Level
5
at 2-Wire at VX 6 Total Harmonic Distortion
8
Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. Typical figures are at 25C and are for design aid only.
Note 1: All of the above characteristics use a test circuit as per Figure 3. Note 2: All of the above test conditions use a test source impedance which matches the device's impedance. Note 3: dBm is referenced to 600 unless otherwise stated.
2-25
MH88422
AC Electrical Characteristics - MH88422-1
Characteristics 1 2 2-Wire input Impedance (200 + 820 //115nF) Return Loss at 2-Wire (200 + 820 //115nF) Longitudinal to Metallic Balance Sym Zin RL 20 20 20 40 55 53 Nc at 2-Wire At VX 5 6 Transmit Gain (2-Wire to VX) Frequency Response Gain (relative to gain @ 1kHz) -72 -72 -0.4 -0.6 -0.6 -58 Min Typ 900 22 24 26 65 60 60 Max
Preliminary Information
Units dB dB dB dB dB dB dBmp dBmp dB dB dB
Test Conditions @ 1kHz 300-500Hz 500-2500Hz 2500-3400Hz 50-300Hz 300-1000Hz 1000-4000Hz
3
4
Idle Channel Noise
Input 0.5V @ 1kHz Off -Hook 300Hz 3400Hz
Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. Typical figures are at 25C and are for design aid only.
AC Electrical Characteristics - MH88422-2
Characteristics 1 2 3 2-Wire Input Impedance (600) Return Loss at 2-Wire (Reference 600) Longitudinal to Metallic Balance Metallic to Longitudinal Balance Sym ZIn ERL SFRL 20 14 58 53 60 40 Nc at 2-Wire at VX 5 6 Transmit Gain (2-Wire to Vx) Frequency Response Gain (relative to gain @ 1kHz) 13 13 -0.4 -0.6 -0.6 20 dBrnC dBrnC dB dB dB Input 0.5V @ 1kHz Off- Hook 200Hz 3400Hz Min Typ 600 20 18 60 55 Max Units dB dB dB dB dB Test Conditions @ 1kHz 500-2500Hz 200-3200Hz 200-1000Hz 1k-3kHz 200-1000Hz 1k-4kHz
4
Idle Channel Noise
Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. Typical figures are at 25C and are for design aid only.
2-26
Preliminary Information
AC Electrical Characteristics - MH88422-3
Characteristics 1 2 3 4 2-Wire Input Impedance (370 + 620 // 310nF) Return Loss at 2-Wire (370 + 620 // 310nF) Longitudinal to Metallic Balance Idle Channel Noise at 2-Wire at VX 5 6 Transmit Gain (2-Wire to Vx) Frequency Gain (relative to gain @ 1kHz) Nc -80 -80 -0.4 -0.6 -0.6 -70 -68 dBmp dBmp dB dB dB Sym Zin RL 18 50 Min Typ 700 20 60 Max Units dB dB
MH89770
Test Conditions @ 1kHz 200-2400Hz 300-3400Hz
Input 0.5V @ 1kHz Off-Hook 300Hz 3400Hz
AC Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. Typical figures are at 25C and are for design aid only.
Note 1: All of the above characteristics use a test circuit as per Figure 3. Note 2: All of the above test conditions use a test source impedance which matches the device's impedance. Note 3: dBm is referenced to 600 unless otherwise stated.
TIP-RING Drive Circuit
The audio input ground (AGND) referenced signal at VR, biased at 2.5V, is converted to a balanced output signal at Tip-Ring. 2-4 wire isolation is achieved through the use of optocouplers when the LC input is activated, low, and loop current flowing.
The output impedance of the VX output is about 10, therefore, with two external 1k resistors configured as per Figure 5, this will result in 6dB of attenuation for a total gain of -6.4dB. For correct gain, the MH88422 input impedance must match the line impedance.
Receive Gain
Receive Gain (VR to Tip-Ring) is fixed as indicated in "AC Electrical Characteristics". However, by adding a single external resistor in series with the VR input, the Receive Gain can be reduced. Overall Receive Gain = 3.5dB + 20log (47k /(47k + Rext), The input impedance of the VR input is 47k, therefore, an external 100k resistor in series with this input will result in 10dB of attenuation for a total gain of -6.5dB. For correct gain, the MH88422 input impedance must match the line impedance.
TIP-RING Receive Circuit
The differential audio signal at Tip-Ring is converted to a ground (AGND) referenced signal, biased at 2.5V, at the VX output. 2-4 Wire isolation is achieved through the use of optocouplers. The receive circuit operated when LC is low and loop current is flowing
Transmit Gain
Transmit Gain (Tip-Ring to VX) is fixed as indicated in "AC Electrical Characteristics". However, by adding external resistors to the VX output, the Transmit Gain can be reduced as shown in Figure 5. To limit the output current drawn, the minimum recommended resistance to ground is 2k. Overall Transmit Gain = -0.4 dB + 20log (R4 / (R4 + R3))
2-27
MH88422
Preliminary Information
14 TIP 13 RLS
MH88422
VX
6
Audio Output
VR TIP 11 C2 D1 10 9 RING RING 1 VDD AGND TXIN TF RVLC
7
Audio Input
4
Ring Voltage & Loop Current Detect Output
LC 2
3
Loop Control Input
+
C1
+5V
NOTES:
1) C1: 10F, 6V Tantalum 2) C2: 0.1F, 250V (Typical Value) 3) D1: 180VDC Foldback Diode, e.g. TISP4180, TISP5180 4) VX and VR are biased at 2.5V, therefore, coupling capacitors may be required depending on application.
Calls are set up and cleared in this mode by the external controller. It turns on the loop via Loop Control, dialling by pulsing loop control (or via DTMF tones) and clearing down by turning Loop Control off.
Figure 3 - Typical Application Circuit
14 TIP R6 TIP K1a 13 RLS 11
MH88422
VX
6 Audio Output 7
TF
D1 RING Line Relay Input K1b C2 K1 9 RING 10 TXIN
R2 Internal dummy Ringer Resistor
VR
Audio Input
RVLC
4
Ring Voltage & Loop Current Detect Output
3 LC VDD AGND 2 + C1 Loop Control Input
1
NOTES: R2 & C2 form a dummy ringer, where R2 is on the hybrid and C2 must be fitted by the customer. To initate a manual call, lift the handset. The RVLC pin will indicate that the line has been seized by the monitor phone. The required number is then dialled and the connections established. During this phase the Loop Control input should be turned ON to ensure that when the relay K1 is operated and the monitor phone removed from the line loop current is still maintained. On receipt of the correct progress tones the external controller should control the data transmission and clear down the call when it is completed by turning the Loop Control OFF. For applications in some countries such as Germany the MH88422 can not be used with an optional telephone but may still be used in a combined telephone/fax machine.
1) C1: 10F, 6V Tantalum 2) C2: 0.47F, 100V +5V K1b 3) D1: 180VDC Foldback Diode, e.g. TISP4180, TISP5180 4) VX and VR are biased at 2.5V, therefore, coupling capacitors may be required depending on application. 5) R6 adjust the monitor phone detect sensitivity typically set to 200 ohms for 5mA limit on the -1 variant and 75 ohms on the -3 variant. 6) K1b is added to remove the dummy ringer when using a combined phone on the-1 variant and is not required for all other variants.
Figure 4 - Typical Application Circuit with Dummy Ringer and Monitor Phone
2-28
Preliminary Information
MH88422
14 TIP 13 TIP 11 C2 D1 10 TF RLS
MH88422
VX
6
R3
R4 Audio Output
7 VR
100k Audio Input R5
4 RVLC
Ring Voltage & Loop Current Detect Output
TXIN 3
RING
9
RING VDD 1 AGND 2
LC
Loop Control Input
RECEIVE GAIN: Audio input to Tip-Ring =20log(47k/(R5+47K))+3.5dB
+
C1
= -6.5dB
TRANSMIT GAIN: Tip-Ring to Audio Output =20log(R4(R3+R4))-0.4dB
+5V
1) C1: 10F, 6V Tantalum 2) C2: 0.1F, 250V (Typical Value) 3) D1: 180VDC Foldback Diode, e.g. TISP4180, TISP5180 4) VX and VR are biased at 2.5V, therefore, coupling capacitors may be required depending on application. 5) (R3+R4) should be > 2k to prevent overload.
= -6.4dB
Note: The VX output gain has been reduced by 6dB (to -6.4dB) and the VR input gain has been reduced by 9.9dB (to -6.4dB) in this example.
Figure 5 - Typical Application Circuit for Gain Adjustment
14 TIP 13 TIP RLS
MH88422
VX
6
10F
Audio Output Audio Input
11 C2 D1 10
TF TXIN
VR
7
10F
4 RVLC Current Detect Output Ring Voltage & Loop
RING Meter Pulse Filter
9
3 RING 1 LC VDD AGND Loop Control Input 2
Meter Pulse Detector
+
C1
+5V
1) C1: 10F, 6V Tantalum 2) C2: 0.1F, 250V (Typical Value) 3) D1:180VDC Foldback Diode, e.g. TISP4180, TISP5180.
Note: Meter pulses at high frequency (16kHz or 12kHz) and high level (10V RMS) are used in some countries. The VX amplifier has a low pass filter which attenuates by typically 15dB at 16kHz (For the -1 variant). If this proves insufficient for specific applications, an LC reject filter is recommended.
Figure 6 - Typical Application Circuit with Meter Pulse Filter and Coupling Capacitor
2-29
MH88422
Preliminary Information
14 TIP 13 RLS TIP 11 C2 D1 10 TF TXIN
MH88422
VX
6 Audio Output 7 Audio Input
VR
R2
RVLC
4
Ring Voltage & Loop Current Detect Output
RING
9 RING 1 VDD AGND
LC 2
3 Loop Control Input
+
C1
+5V
Notes:
1) C1: 10F, 6V Tantalum 2) C2:1.8F, 250V (Normally in master socket) 3) D1:180VDC Foldback Diode, e.g. TISP4180, TISP5180
Figure 7 -Typical Application Circuit showing UK Dummy Ringer Circuit.
0.19 Max (4.8 Max) 0.27 Max (6.9 Max) 0.08 Typ (2 Typ) * 0.200+0.010 (5.08+0.25) 0.020 + 0.005 (0.5 + 0.12) 0.10 Typ (2.54 Typ) 0.26+0.015 (6.6+0.4)
0.063 Max(1.6 Min)
AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAA AAAAAAAA AAA AAAAAAAAAAAAAAAAAAAAAAA AAAA AAAA 0.90 Typ (22.9 Typ)
0.95 Max (24.2 Max)
1.42 Max (36.1 Max)
Notes: 1) Not to scale 2) Dimensions in inches). 3) (Dimensions in millimetres). *Dimensions to centre of pin.
1
Figure 8 - Mechanical Data for 14 Pin DIL Hybrid
2-30
Preliminary Information
MH88422
0.19 Max (4.8 Max)
0.063 Max (1.6 Max) 0.10 Typ (2.54 Typ) * 0.20 + 0.005 (5.0 + 0.12)
0.33 Max (8.4 Max) 0.08 Typ (2 Typ) * 0.20 + 0.010 (5.08 + 0.25)
AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAA
0.060 Typ (1.52) 1.42 Max (36.1 Max)
AAAAAA AAAAAA AAAAAA AAAAAA AAAAAA AAAAAA AAAAAA AAAAAA AAAAAA AAAAAA AAAAAA
0.125+0.015 (3.18+0.38)
1.08 Max (27.4 Max)
Notes: 1) Not to scale 2) Dimensions in inches). 3) (Dimensions in millimetres). *Dimensions to centre of pin.
Figure 9 - Mechanical Data for 14 Pin Surface Mount Hybrid
0.1 (2.5)
0.89 (22.6)
0.04 (1.02)
0.16 (4.06)
Figure 10 - Recommended Footprint for 14 Pin Surface Mount Hybrid
2-31
MH88422
Notes:
Preliminary Information
2-32

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