MH88422 Line Interface Circuit Preliminary Information ISSUE 5 Features • FAX and Modem interface (V29/V22 bis) • Variants match German, UK & 600Ω network impedances Ordering Information • 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 Interface to Central Office for: • DAA Modem • FAX • Answering Machine • Terminal Equipment MH88422-1 MH88422-2 MH88422-3 14 Pin DIL Package 14 Pin DIL Package 14 Pin DIL Package Surface Mount Options are available by adding the Suffix “S” Description Applications • April 1995 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 600Ω variants (-2). Isolation Barrier VDD Power Supply TIP RING TXIN OptoIsolation Logic Input Buffer LC OptoIsolation Audio Buffer VR Audio Input Buffer OptoIsolation Audio Buffer Input Buffer OptoIsolation Ring & Loop Active Termination TF RLS AGND NETWORK CONNECTIONS Transhybrid Loss Cancellation Circuit VX RVLC Buffer USER 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 # Name 1 VDD 2 AGND 3 LC 4 RVLC 5 NC No Connection should be made to this pin. 6 VX Transmit (Output). 4-Wire ground (AGND) referenced audio output, biased at 2.5V. Outputs in off-hook mode only. 7 VR Receive (Input). 4-Wire ground (AGND) referenced audio input, biased at 2.5V. LC must be activated low and loop current must be flowing. 8 NC No Connection should be made to this pin. 9 RING 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. 10 TXIN Transmit (Input). Connects to the “Ring” lead of the central office through a coupling capacitor. 11 TF Tip Feed. Connects to the “Tip” lead of the central office through an internal resistor and an optional external resistor. 12 NC No Connection should be made to this pin. 13 RLS Ring Loop Sense (Input). Sense node for ringing voltage detector and the loop current detector. 14 TIP 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. 2-22 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. MH88422 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. 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. 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 300Ω (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. 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. 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. 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. 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 = 600Ω MH88422-3 Zin = 370 + 620 // 310nF UK 2-23 MH88422 Preliminary Information . Absolute Maximum Ratings* - All voltages are with respect to AGND unless otherwise specified. Parameter Symbol Min Max Units 1 DC Supply Voltage VDD -0.3 6 V 2 Storage Temperature TS -55 +80 °C 3 DC Loop Voltage VBat -100 +100 V 4 Ringing Voltage VR - 120 VRMS 5 Loop Current ILoop - 90 mA * Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied Recommended Operating Conditions. Parameters Sym Min Typ‡ Max Units 5.0 5.5 V 70 °C 1 DC Supply Voltages VDD 4.5 2 Operating Temperature TOP 0 3 Ringing Voltage VR 75 VRMS Test Conditions VBat=-48V ‡ Typical figures are at 25°C with nominal +5V supply and are for design aid only Loop Electrical Characteristics* Characteristics 1 Sym Ringing Voltage -1 Variant only No Detect Detect VR Ringing Voltage All other Variants No Detect Detect VR 2 Ringing Frequency 3 On-Hook 2-wire Impedance 4 Operating Loop Current 5 Operating Loop Resistance 6 Off-Hook DC Voltage Max Units Test Conditions 20 VRMS VRMS Refer to FT2 1TR2 for test method 7 VRMS VRMS Externally Adjustable 68 Hz 27 14 Ω 40k 15 -1 Variant -3 Variant 7 Leakage Current (2-Wire to AGND) 8 Leakage Current on Hook (Tip to Ring) 9 DC Resistance during dialling -1 variant only Dial Pulse Distortion -1 Variant All other Variant Typ‡ 15 -2 Variant 10 Min ON OFF 80 mA 2800 Ω VBat=-48V, ILoop=15mA 9.6 15 6.0 7.8 9.0 12.5 V V V V V V ILoop=25mA ILoop=42mA ILoop=15-20mA ILoop=26mA ILoop=25mA ILoop=42mA 10 µA 100VDC 9 10 µA VBat=-50V 200 220 Ω ILoop=20-40mA +2 +8 +2 +4 +10 +4 ms ms ms 6.0 6.0 4.0 4.0 6.0 6.0 0 +6 0 * Loop Electrical Characteristics are over recommended operating conditions unless otherwise stated. ‡ Typical figures are at 25°C and are for design aid only. Note 1: All of the above characteristics use a test circuit as per Figure 3. 2-24 1kHz MH88422 Preliminary Information DC Electrical Characteristics† Characteristics Sym Min Typ‡ Max Units Test Conditions 1 Supply Current IDD 3 mA VDD = -5.0V, Idle state 2 Power Consumption PC 15 mW VDD = -5.0V, Idle state Low Level Output Voltage High Level Output Voltage VOL VOH Low Level Input Voltage High Level Input Voltage Low Level Input Current High Level Input Current VIL VIH IIH IIL 3 4 5 RVLC LC 0.4 V V 0.8 V V µΑ µA 2.4 2.0 60 60 IOL = 4mA IOH = 0.4mA VIH = 5.0V VIL = 0.0V † DC Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. ‡ Typical figures are at 25°C with nominal+ 5V supplies and are for design aid only. AC Electrical Characteristics† - MH88422 All Variants Characteristics Sym Min Typ‡ Max Units Test Conditions 1 Input Impedance VR 47k Ω 2 Output Impedance at VX 10 Ω 3 Receive Gain (VR to 2-wire) 3.5 dB Input 0.5V at 1kHz 0 0 dB dB 300 Hz 3400 Hz 4 5 Frequency Response Gain (relative to Gain @ 1kHz) THD <5% @ 1kHz ILoop =15 to 40mA Signal Output Overload Level at 2-Wire at VX 6 Total Harmonic Distortion 8 Power Supply Reject Ratio at 2-wire at VX Transhybrid Loss +3.0 dBm +2.0 +3.0 dBm 1.2 1.2 % % 30 30 dB dB 20 dB THD at 2-wire at VX 7 +2.0 PSRR THL VDD=4.5V to 5.5V Input -10dB at 1kHz DC loop = 25mA VDD=5.0V Ripple 0.1V,1kHz on VDD Input -3.5dBm, 1kHz at VR † Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. ‡ Typical figures are at 25°C 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 600Ω unless otherwise stated. 2-25 MH88422 Preliminary Information AC Electrical Characteristics† - MH88422-1 Characteristics Sym 1 2-Wire input Impedance (200Ω + 820Ω //115nF) Zin 2 Return Loss at 2-Wire (200Ω + 820Ω //115nF) RL 3 Longitudinal to Metallic Balance 4 Idle Channel Noise Min Typ‡ Max Units Test Conditions 900 Ω @ 1kHz 20 20 20 22 24 26 dB dB dB 300-500Hz 500-2500Hz 2500-3400Hz 40 55 53 65 60 60 dB dB dB 50-300Hz 300-1000Hz 1000-4000Hz Nc at 2-Wire At VX -72 -72 -58 dBmp dBmp 5 Transmit Gain (2-Wire to VX) -0.4 dB Input 0.5V @ 1kHz Off -Hook 6 Frequency Response Gain (relative to gain @ 1kHz) -0.6 -0.6 dB dB 300Hz 3400Hz † Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. ‡ Typical figures are at 25°C and are for design aid only. AC Electrical Characteristics† - MH88422-2 Characteristics Sym 1 2-Wire Input Impedance (600Ω) 2 Return Loss at 2-Wire (Reference 600Ω) 3 Longitudinal to Metallic Balance Metallic to Longitudinal Balance 4 Idle Channel Noise Min Max Units Test Conditions 600 Ω @ 1kHz 20 14 20 18 dB 500-2500Hz 200-3200Hz 58 53 60 40 60 55 dB dB dB dB 200-1000Hz 1k-3kHz 200-1000Hz 1k-4kHz ZIn ERL SFRL Typ‡ Nc at 2-Wire at VX 13 13 20 dBrnC dBrnC 5 Transmit Gain (2-Wire to Vx) -0.4 dB Input 0.5V @ 1kHz Off- Hook 6 Frequency Response Gain (relative to gain @ 1kHz) -0.6 -0.6 dB dB 200Hz 3400Hz † Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. ‡ Typical figures are at 25°C and are for design aid only. 2-26 MH89770 Preliminary Information AC Electrical Characteristics† - MH88422-3 Characteristics Sym 1 2-Wire Input Impedance (370Ω + 620Ω // 310nF) Zin 2 Return Loss at 2-Wire (370Ω + 620Ω // 310nF) RL 3 Longitudinal to Metallic Balance 4 Idle Channel Noise Min Typ‡ Max Units Test Conditions 700 Ω @ 1kHz 18 20 dB 200-2400Hz 50 60 dB 300-3400Hz Nc at 2-Wire at VX -80 -80 -70 -68 dBmp dBmp 5 Transmit Gain (2-Wire to Vx) -0.4 dB Input 0.5V @ 1kHz Off-Hook 6 Frequency Gain (relative to gain @ 1kHz) -0.6 -0.6 dB dB 300Hz 3400Hz † AC Electrical Characteristics are over Recommended Operating Conditions unless otherwise stated. ‡ Typical figures are at 25°C 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 600Ω 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. 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 2kΩ. The output impedance of the VX output is about 10Ω, therefore, with two external 1kΩ 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 (47kΩ /(47kΩ + Rext), The input impedance of the VR input is 47kΩ, therefore, an external 100kΩ 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. Overall Transmit Gain = -0.4 dB + 20log (R4 / (R4 + R3)) 2-27 MH88422 Preliminary Information MH88422 14 VX TIP 6 Audio Output 13 RLS VR 7 Audio Input TIP 11 TF C2 D1 RVLC TXIN 10 RING Ring Voltage & Loop Current Detect Output 9 RING 4 LC VDD 3 Loop Control Input AGND 1 2 + C1 +5V NOTES: 1) C1: 10µF, 6V Tantalum 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. 2) C2: 0.1µF, 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. Figure 3 - Typical Application Circuit MH88422 14 VX TIP R6 K1a Audio Output 13 RLS TIP 11 R2 Internal dummy Ringer Resistor TF D1 VR RVLC 7 4 RING 10 K1b C2 TXIN Ring Voltage & Loop 3 LC VDD 1 K1 Audio Input Current Detect Output 9 RING Line Relay Input 6 Loop Control Input AGND 2 + C1 1) C1: 10µF, 6V Tantalum 2) C2: 0.47µF, 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. 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. Figure 4 - Typical Application Circuit with Dummy Ringer and Monitor Phone 2-28 MH88422 Preliminary Information MH88422 14 VX TIP 13 RLS 6 7 R4 R3 Audio Output 100k VR Audio Input TIP 11 C2 D1 10 R5 TF Ring Voltage & Loop 4 RVLC Current Detect Output TXIN 3 9 RING RING Loop Control Input LC AGND VDD 1 2 + RECEIVE GAIN: Audio input to Tip-Ring =20log(47k/(R5+47K))+3.5dB C1 = -6.5dB +5V TRANSMIT GAIN: Tip-Ring to Audio Output =20log(R4(R3+R4))-0.4dB 1) C1: 10µF, 6V Tantalum = -6.4dB 2) C2: 0.1µF, 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 > 2kΩ to prevent overload. 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 MH88422 14 VX TIP 13 TIP 11 C2 D1 10 6 10µF Audio Output RLS VR TF Audio Input 7 10µF 4 Ring Voltage & Loop RVLC TXIN Current Detect Output 9 RING Meter Pulse Detector Meter Pulse Filter 3 RING LC VDD 1 AGND + Loop Control Input 2 C1 +5V 1) C1: 10µF, 6V Tantalum 2) C2: 0.1µF, 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 MH88422 14 VX TIP 6 Audio Output 13 RLS VR 7 Audio Input TIP 11 C2 D1 10 TF R2 RVLC TXIN Ring Voltage & Loop Current Detect Output 9 RING 4 RING LC Loop Control Input AGND VDD 1 3 + 2 C1 +5V Notes: 1) C1: 10µF, 6V Tantalum 2) C2:1.8µF, 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) 0.063 Max(1.6 Min) 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) 0.95 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 AAAA AAAAAAAA AAAAAAAA AAAAAAAA AAAAAAAA AAAAAAA AAA AAAA AAAAAAAA AAAAAAAA AAAAAAAA AAAAAAAA AAAAAAA AAA AAAA AAAA AAAA AAAA AAAA AAA AAAA AAAAAAAAAAAAAAA AAAAAAAA AAA AAAA AAAA AAAA AAAA AAAAAAAAAAAAAAAAAAAAAAA AAAA AAAAAAAAAAAAAAAAAAA 0.90 Typ (22.9 Typ) MH88422 Preliminary Information 0.19 Max (4.8 Max) 0.33 Max (8.4 Max) 0.063 Max (1.6 Max) * 0.10 Typ (2.54 Typ) 0.20 + 0.005 (5.0 + 0.12) AAA AAAA AAAAAAAA AAAAAAAA AAAAAAAA AAAAAAAA AAAAAAA AAAAAAAAAAAAAAAAAAAAAAA AAAA AAAA AAAA AAAA AAAA AAA AAAAAAAAAAAAAAAAAAAAAAA AAA AAAA AAAAAAAA AAAAAAAA AAAAAAAA AAAAAAAA AAAAAAA AAAAAAAAAAAAAAAAAAAAAAA 0.08 Typ (2 Typ) * 0.20 + 0.010 (5.08 + 0.25) 0.060 Typ (1.52) 1.42 Max (36.1 Max) AAAAAA AAAAAA AAAA AAAAAA AA AAAAAA AAAAAA AAAA AA AAAA AAAAAA AA AAAAAA AA AAAA 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: 2-32 Preliminary Information