PDF MH88435-P Data sheet ( Hoja de datos )

Número de pieza	MH88435-P
Descripción	Data Access Arrangement Preliminary Information
Fabricantes	Mitel Networks
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Features • FAX and Modem interface V.34(33k6) • Externally programmable line and network balance impedances • Programmable DC termination characteristics • IEC950 recognised component • Transformerless 2-4 Wire conversion • Integral Loop Switch • Dial Pulse and DTMF operation • Accommodates parallel phone detection • Line state detection outputs:- loop current/ringing voltage/line voltage • Single +5V operation, low on-hook power (35mW) • Full duplex voice and data transmission • On-Hook reception from the line • Approvable to UL1950 • Industrial temperature range available Applications Interface to Central Ofﬁce or PABX line for: • FAX/Modem (including software modems) • Electronic Point of Sale • Security System • Telemetry • Set Top Boxes MH88435-P Data Access Arrangement Preliminary Information DS5132 ISSUE 8 July 1999 Package Information MH88435AD-P 28 Pin DIL Package MH88435AS-P 28 Pin SM Package 0°C to +70°C MH88435AS-PI 28 Pin SM Package MH88435AD-PI 28 Pin DIL Package -40°C to +85°C Description The Mitel MH88435 Data Access Arrangement (D.A.A.) provides a complete interface between audio or data transmission equipment and a telephone line. All functions are integrated into a single thick ﬁlm hybrid module which provides high voltage isolation, very high reliability and optimum circuit design, needing a minimum of external components. The impedance and network balance are externally programmable, as are the DC termination characteristics, making the device suitable for most countries worldwide. TIP RING Input Buffer & Line Termination Isolation Barrier Opto- Isolation Logic Input Buffer Isolation Analog Buffer VLOOP1 VLOOP2 Isolation Analog Buffer Isolation Ring & Loop Buffer THL cancellation and line impedance matching circuit Network Connections User Connections Figure 1 - Functional Block Diagram VCC VBIAS AGND LC VR+ VR- NB1 NB2 VX ZA RV LCD LOOP RS 2-39 1 page Preliminary Information MH88435-P R7 = 30 kΩ x (Desired Threshold Voltage - 10Vrms) Therefore, 300k kΩ gives ~ 20Vrms and 600k kΩ gives ~ 30Vrms An AC ringing voltage across Tip and Ring will cause RV to output TTL pulses at the ringing frequency, with an envelope determined by the ringing cadence. Parallel Phone and Dummy Ringer An external parallel phone or dummy ringer circuit can be connected across Tip and Ring as shown in Figure 5. A dummy ringer is an AC load which represents a telephone’s mechanical ringer. In normal circumstances when a telephone is on- hook and connected to the PSTN, its AC (Ringer) load is permanently presented to the network. This condition is used by many PTT’s to test line continuity by placing a small AC current onto the line and measuring the voltage across tip (A) and ring (B). Today’s telecom equipment may not have an AC load present across tip and ring (e.g. modems), therefore any testing carried out by the PTT will see an open circuit across tip and ring. In this instance the PTT assumes that the line continuity has been damaged. To overcome this problem many PTT’s specify that a "Dummy Ringer" is presented to the network at all times. Ideally its impedance should be neglible in the audio band, and high at the ringing frequencies (e.g. 25Hz). Note that the requirement for the "Dummy Ringer" is country speciﬁc. Parallel phone detection is used mostly in set-top box applications. This is when a modem call will need to be disconnected from the central ofﬁce by the equipment when the parallel phone is in the off- hook state. This is so that a call can be made to the emergency services. To detect this state, additional circuitry will be required and can be found in the application note, MSAN-154. 2-4 Wire Conversion The device converts the balanced 2-Wire input, presented by the line at Tip and Ring, to a ground referenced signal at VX, biased at 2.0V. This simpliﬁes the interface to a modem chip set. Conversely, the device converts the differential signal input at VR+ and VR- to a balanced 2-Wire signal across Tip and Ring. The device can also be used in a single ended mode at the receive input, by leaving VR+ open circuit and connecting the input signal to VR- only. Both inputs are biased at 2.0V. During full duplex transmission, the signal at Tip and Ring consists of both the signal from the device to the line and the signal from the line to the device. The signal input at VR+ and VR- being sent to the line, must not appear at the output VX. In order to prevent this, the device has an internal cancellation circuit. The measure of this attenuation is Transhybrid Loss (THL). The MH88435 has the ability to transmit analog signals from Tip and Ring through to VX when on- hook. This can be used when receiving caller line identiﬁcation information. Transmit Gain The Transmit Gain of the MH88435 is the gain from the differential signal across Tip and Ring to the ground referenced signal at VX. The internal Transmit Gain of the device is ﬁxed as shown in the AC Electrical Characteristics table. For the correct gain, the Input Impedance of the MH88435, must match the speciﬁed line impedance. By adding an external potential divider to VX, it is possible to reduce the overall gain in the application. The output impedance of VX is approximately 10Ω and the minimum resistance from VX to ground should be 2kΩ. Example: If R3 = R4 = 2kΩ, in Figure 5, the overall gain would reduce by 6.0dB. 2-43 5 Page Preliminary Information = Ground (Earth) 11 13 15 3 LOOP VR+ RS LCD TIP 28 4 VR- 5 VX NB1 1 MH88435 21 SC NB2 2 22 SC 360K 24 VLOOP2 RING 27 25 VLOOP1 VBIAS 10 LC RV AGND VCC ZA 1K 6 16 8 9 7 5V 4.7K ILOOP 15K 10uF 5V Figure 6 - Test Circuit 1 MH88435-P -V 11 13 15 = Ground (Earth) 3 LOOP VR+ RS LCD TIP 28 4 VR- 5 VX NB1 1 MH88435 21 SC NB2 2 22 SC 360K 24 VLOOP2 RING 27 25 VLOOP1 VBIAS 10 LC RV AGND VCC ZA 1K 6 16 8 9 7 5V 4.7K 15K 10uF 10H 500Ω 100uF I=20mA + 100uF + 10H 500Ω Gain = [20 * Log (VX / Vs)] + 6.02 dB 5V Figure 7 - Test Circuit 2 Vs Impedance = Zin 2-49 11 Page

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