MH88400 Line Interface Circuit Preliminary Information ISSUE 1 Features • FAX and Modem interface • Suitable for V.29 FAX & V.22 bis Data • Allows caller identification • Variants match German, UK, 600Ω & 900Ω network impedances • Isolation circuitry conforms 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 -monitor phone switch hook Single +5V operation April 1995 Ordering Information MH88400-1 14 Pin DIL Package MH88400-2 14 Pin DIL Package MH88400-3 14 Pin DIL Package 0°C to 70°C Description The Mitel MH88400 Line Interface Circuit provides a complete audio and signalling link between audio equipment and central office. The functions provided by the MH88400 include 2-4 Wire conversion, loop seizure, external monitor phone switch hook status and ringing voltage and loop current detection. The device is fabricated as a thick film hybrid which incorporates various technologies for optimum circuit design, high voltage isolation and very high reliability. Applications Interface to Central Office for: • DAA • Modem • FAX • Answering Machine • Terminal Equipment Variants are provided to meet German (-1) and UK (-3) and general 600Ω (-2) line impedance (see section on Line Impedances). Isolation Barrier Transformer Isolation Power Supply VDD AGND TIP Active Termination RING TXIN Audio Input Buffer OptoIsolation Audio Buffer VR OptoIsolation Logic Input Buffer LC OptoIsolation Audio Buffer VX OptoIsolation Ring & Loop Buffer RVLC Switch Hook Buffer SHK TF RLS Input Buffer PHS OptoIsolation NETWORK CONNECTIONS USER CONNECTIONS Figure 1 - Functional Block Diagram 2-11 MH88400 Preliminary Information VDD AGND LC RVLC SHK VX VR 1 2 3 4 5 6 7 14 13 12 11 10 9 8 TIP RLS PHS TF TXIN RING NC Figure 2 - Pin Connections Pin Description Pin # Name 1 VDD 2 AGND 3 LC 4 RVLC 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 MH88400 in the off- hook mode. The RVLC outputs pulses when the external monitor phone is dial pulsing or when the MH88400 is dial pulses via the LC input. In addition, when the MH88400 is in the on-hook mode, a pulsing output indicates that ringing voltage is across the Tip and Ring leads; the pulsing outputs frequency is twice the ringing frequency. 5 SHK Switch Hook Detect (Output). This is an optional output which can be used with the PHS input and an external phone. When loop current flows from PHS to TIP, SHK goes to logic low. 6 VX Transmit (Output). 4-Wire ground(AGND) referenced audio output, biased at 2.5V. Outputs for both off-hook and on-hook. 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. This pin is not connected internally 9 RING Ring Lead. Connects to the “Ring” lead of the central office through a 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 PHS Monitor Phone Sense (Input). This is an optional input which can be used with the SHK output and an external phone. When loop current flows from PHS to TIP, SHK goes to logic low. 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. 2-12 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 MH88400 Preliminary Information Functional Description The MH88400 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 MH88400 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. In addition, when the MH88400 is in the on-hook mode, 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 MH88400. It also converts the receive ground referenced signal at VR (Receive) of the MH88400 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. Consequently, both of these signals will appear 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). 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 simpler to a resistance of approximately 300Ω (loop current dependant). 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. 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 due to the external monitor phone or due to the MH88400 being in the off-hook mode is detected. A simple THL cancellation circuit as shown in figure 7 can be used for certain applications to give the required VX/VR signal separation. The MH88400 is then suitable to drive a COMBO 2 CODEC or a VLSI MODEM device. Line Impedance The MH88400 is suitable to drive a COMBO 2 CODEC or a VLSI modem device. The MH88400 provides a fixed Tip-Ring impedance which conforms to the following PTT requirements. MH88400-1 Zin = 200 + 820 // 115nF Germany FTZ MH88400-2 600Ω MH88400-3 Zin = 370 + 620 // 310nF UK BSI The RVLC outputs pulses when the external monitor phone is dial pulsing or when the MH88400 is dial pulsing via the LC mode. 2-13 MH88400 Preliminary Information . Absolute Maximum Ratings* - All voltages are with respect to AGND unless otherwise specified. Parameter Symbol Min Max Units VDD -0.3 6 V TS -55 +80 °C 1 DC Supply Voltage 2 Storage Temperature 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 supplies and are for design aid only. Loop Electrical Characteristics* Characteristics 1 Ringing Voltage Sym No Detect Detect 2 Ringing Frequency 3 On-Hook 2-wire Impedance 4 Operating Loop Current 5 Operating Loop Resistance 6 Off-Hook DC Resistance Min VR 15 Units 20 VRMS VRMS 68 Hz Ω 40k 10 -1 & -2 Variants 7 Leakage Current (2-Wire to AGND) 8 Leakage Current on Hook (Tip to Ring) 9 DC Resistance during dialling -1 variant Dial Pulse Distortion Max 27 310 160 -3 Variant 10 Typ‡ 350 300 250 400 9 ON Off mA 4000 Ω VBAT=-48V, ILoop=10mA 480 480 300 450 Ω Ω Ω Ω ILoop=20mA ILoop=40mA ILoop=40mA ILoop=20mA 10 µA 100VDC 10 µA VBAT=50V Ω ILoop=20-40mA 220 +4 0 +8 +2 ms ms * Loop Electrical Characteristics are over recommended operating conditions unless otherwise stated. ‡ Typical figures are at 25°C and are for design aid only. Note: All of the above characteristics use a test circuit as per Figure 3. 2-14 1kHz 80 200 0 Test Conditions MH88400 Preliminary Information DC Electrical Characteristics † Characteristics Sym Min Typ‡ Max Units Test Conditions 1 Supply Current IDD 15 mA VDD = 5.0V, ILoop=40mA 2 Power Consumption PC 75 mW VDD = -5.0V,ILoop=40mA Low Level Output Voltage High level Output Voltage VOL VOH Low Level Input Voltage High level Input Voltage High Level Input Current Low Level Input Current VIL VIH IIH IIL 3 4 5 RVLC SHK 0.4 V V 0.9 V V mΑ µA 3.8 3.5 0.6 1 IOL = 1.0mA IOH = 1.0mA 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. Note: See figure 3a and 3b. AC Electrical Characteristics† - MH88400 All Variants Characteristics Sym Min Typ‡ Max Units 1 Input Impedance VR 47 kΩ 2 Output Impedance at VX 5 Ω 3 Transmit Gain (2-Wire to VX) dB Input 0.5V at 1kHz offhook dB dB 300 Hz 3400 Hz dB Input 0.5V at 1kHz dB dB 300 Hz 3400 Hz -0.4 4 Frequency Response Gain (relative to Gain @ 1kHz) 5 Receive Gain (VR to 2-wire) -2.4 -3.0 Test Conditions 3.5 6 Frequency Response Gain (relative to Gain @ 1kHz) 7 Signal Output Overload Level 0 0 THD <5% @ 1kHz ILoop =10-40mA at 2-Wire at Vx 8 Total Harmonic Distortion dBm dBm dBm VDD=4.5V VDD=5.0V VDD=5.5V -3.0 0.0 +2.0 dBm dBm dBm VDD=4.5V VDD=5.0V VDD=5.5V 0.9 1.2 % % 35 10 dB dB THD at 2-wire at VX 9 -3.0 0.0 +2.0 Power Supply Reject Ratio at 2-wire at VX PSRR Input 0.5V at 1kHz DC loop = 1000Ω VDD=5.0V Ripple 0.1V,1kHz on VDD † 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. Note 4: THD is measured with a “Weight” filter. 2-15 MH88400 Preliminary Information AC Electrical Characteristics† - MH88400-1 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 -84 -81 -78 dBmp dBmp † 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. Note 4: THD is measured with “Weight” filter. AC Electrical Characteristics† - MH88400-2 Characteristics Sym 1 2-Wire Input Impedance -2 (600Ω) ZIn 2 Return Loss at 2-Wire (Reference -2 =600Ω) RL 3 Longitudinal to Metallic Balance 4 Idle Channel Noise Min Typ‡ Max Units Test Conditions 600 Ω @ 1kHz 20 24 dB 300-3400Hz 50 60 dB 300-3400Hz Nc at 2-Wire at VX -84 -81 -78 dBrnp dBrnp † AC 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† - MH88400-3 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 700 Ω @ 1kHz 18 20 dB 200-2400Hz 50 60 dB 300-3400Hz Nc at 2-Wire at VX -80 -80 -70 -70 dBmp dBmp † 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. Note 4: THD is measured with “weight” filter. 2-16 Test Conditions MH88400 Preliminary Information Overall Transmit Gain = 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. -0.4 dB + 20log (R4 / (R4 + R3)) The output impedance of the VX output is about 5Ω, 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 MH88400 input impedance must match the line impedance. 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 optical isolation. The LC input is activated, low, and loop current must be flowing. 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. TIP-RING Receive Circuit Overall Receive Gain = 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 a combination of optical isolation and transformerler isolation. The receive circuit operated with or without loop current and LC can be either high or low. Signal reception with no loop current can be used for on-hook reception of, for example, caller identification signals. The input impedance of the VR input is 47kΩ, therefore, an external 100kΩ resistor in series with this input will result in 9.9dB of attenuation for a total gain of -6.4dB. Transmit Gain For correct gain, the MH88400 input impedance must match the line impedance. 3.5dB + 20log (47kΩ /(47kΩ + Rext), Transmit Gain (Tip-Ring to VX) is fixed as indicated in “AC Electrical Characteristics”. 6 MH88400 14 TIP 13 RLS 7 R1 VR TIP 11 Audio Input TF C2 RVLC TXIN D1 Audio Output VX 4 Ring Voltage & Loop Current Detect Output 10 3 9 RING LC RING 1 Loop Control Input AGND VDD + 2 C1 +5V NOTES: 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. 1) C1: 10µF, 6V Tantalum 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) VX and VR are biased at 2.5V, therefore, coupling capacitors may be required depending on application. Figure 3 - Typical Application Circuit 2-17 MH88400 Preliminary Information 14 13 TIP 11 R1 D1 10 R2 MH88400 6 Audio Output VX TIP RLS 7 VR TXIN 9 Current Detect Output 3 LC RING Loop Control Input AGND VDD Line Relay Input Ring Voltage & Loop 4 RVLC C2 RING Audio Input TF 2 1 1) R1: 39Ω,1/2W,5%,current limiting resistor for use in Germany. 2) R2: 18kΩ 3) C1: 10µF, 6V Tantalum 4) C2: 0.47µF, 100V + K1 C1 +5V 5) D1: 180VDC Foldback Diode, e.g. TISP4180, TISP5180 6) VX and VR are biased at 2.5V, therefore, coupling capacitors may be required depending on application. NOTES: C2 must be 0.1µF for correct operation. 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 as 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 14 13 MH88400 TIP 6 R3 R4 1K VX 1K RLS Audio Output 7 VR R1 TIP 11 R2 100K TF 4 C2 D1 10 Audio Input RVLC TXIN Ring Voltage & Loop Current Detect Output 3 9 RING LC RING AGND VDD RECEIVE GAIN: Audio input to Tip-Ring =20log(R2/(R2+47K))+3.5dB =6.5dB 1 + C1 +5V TRANSMIT GAIN: Tip-Ring to Audio Output =20log(R4(R3+R4))-0.4dB =-6.4dB 1) R1: 39Ω,1/2W,5%,current limiting resistor for use in Germany 2) C1: 10µF, 6V Tantalum Note: The VX output gain has been reduced by 6dB (to -6.4dB) and the VR input gain has been reduced by 10dB (to -6.5dB) in this example. 3) C2: 0.1µF, 250V (Typical Value) 4) D1: 180VDC Foldback Diode, e.g. TISP4180, TISP5180 5) VX and VR are biased at 2.5V, therefore, coupling capacitors may be required depending on application. 6) (R3+R4) should be > 2kΩ to prevent overload. Figure 5 - Typical Application Circuit for Gain Adjustment 2-18 Loop Control Input 2 MH88400 Preliminary Information 14 13 MH88400 TIP 1K 11 10 VR C3 7 Audio Input 0.1µF RVLC TXIN 4 Ring Voltage & Loop Current Detect Output RING LC VDD AGND 3 Loop Control Input 2 1 Meter Pulse Detector L1 4.7mH 22nF TF 9 RING C5 RLS C2 D1 R4 Audio Output VX R1 TIP R3 1K 6 + C1 +5V 1) R1: 39Ω,1/2W,5%, current limiting resistor for use in Germany. 2) C1: 10µF, 6V Tantalum 3) C2: 0.1µF, 250V 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. If this proves insufficient for specific applications, an LC notch is recommended. This should provide a further 20dB of rejection at 16 of 12kHz with only 0.5dB of loss at 3.4kHz (after allowing for the overall 6dB loss caused by R3, R4). 4) D1: 180VDC Foldback Diode, e.g. TISP4180, TISP5180. 5) L1: 4.7mH 5%, eg, Siemens B78108-S 6) C5: 22nF 5% for 16kHz 39nF for 12kHz Figure 6 - Typical Application Circuit with Meter Pulse Filter and Coupling Capacitors 560pF 5% 100k 1% 68k From VR 10nF 5% 68k 1% 1% 62k 1% VX Out A1 - A1 + + 100k From VX 100nF 10pF 100k 1% Note: Amplifier A1 provides a frequency equivalent to the VX path in the MH88400. This provides the correct phase/amplitude response to enable cancellation to take place in amplifier A2. Typical THL figures of 15-20dB can be achieved with the values and tolerances shown. The VR input should be driven from a low impedance < 600R. This circuit will function correctly for all variants provided the termination impedance of the external line at the 2W connection is equal to the characteristics impedance of the MH88400. If it is desired to operate with impedances different from the MH88400 impedances, the frequency compensation networks around A1 must be filtered. Because of the wide variety of impedances which are in typical use it is not possible to specify the required values. 100k 0V Figure 7 -Transhybrid Loss (THL) Cancellation Circuit 2-19 MH88400 Preliminary Information L1 14 13 MH88400 TIP 6 RLS VR 11 TIP C4 C3 RVLC 10 9 RING 4 TXIN LC RING Audio Input Ring Voltage & Loop Current Detect Output 3 Loop Control Input AGND VDD L2 7 TF C2 D1 Audio Output VX 2 1 + C1 +5V Notes: 1) C1: 10µF, 6V Tantalum 2) C2: 0.1µF, 250V 3) D1: 180VDC Foldback Diode, e.g. TISP4180, TISP5180 4) C3: 4.7nF; C4: 1.0nF Ceramic 10% 5) L1, L2: 1mH 5%, eg, Siemens B78108-S1105-J Figure 8 - Typical Application Circuit showing Noise Filter Network for Outband noise reduction 1.50 Max (38.0 Max) 1.05 Max (26.7 Max) 0.90 Typ (22.9 Typ) (1.3 Typ) *0.05 Typ 0.35 Max (8.9 Max) 0.12 Min 0.20 Max (3.0 Min 5.1 Max) Notes: 1) Not to scale 2) Dimensions in inches). 3) (Dimensions in millimetres). *Dimensions to centre of pin. *0.11 Typ (2.9 Typ) 0.20 ± 0.005 (0.5 ± 0.12) *0.200 ± 0.005 (5.08 ± 0.12) Figure 9 - Mechanical Data for 14 Pin DIL Hybrid 2-20