MITEL MTH88437AD-P, MTH88437AD-PI, MTH88437AS-PI, MTH88437AS-P Datasheet

Features

• FAX and Modem interface (V.34/V.34+)

• Designed to work at data rates up to 56kbits

• External 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

• +5V operation, low on-hook power (25mW)

• Full duplex voice and data transmission

• On-Hook reception from the line

• Meets French current limit requirements

• Conforms to German dial pulse standards

• Approvable to UL 1950

• Industrial Temperature Range Available

Applications

Interface to Central Ofﬁce or PABX line for:

• FAX/Modem

• Electronic Point of Sale

• Security System

• Telemetry

• Set Top Boxes

Description

The Mitel MH88437 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.

Figure 1 - Functional Block Diagram

Opto-

Isolation

Logic Input

Buffer

Isolation

Analog

Buffer

Analog

Buffer

THL cancellation

impedance

matching

circuit

Isolation Barrier

VCC AGND

LC VR+

TIP

RING

User Connections

Network Connections

Input Buffer

VLOOP1

Ring & Loop

Line Termination

VLOOP2

VRNB1

NB2

LOOP

LCD

VBIAS

and line

DS5060 ISSUE 4 October 1998

Package Information

MH88437AD-P 28 Pin DIL Package MH88437AS-P 28 Pin SM Package

0˚C to 70˚C

MH88437AD-PI Ind. Temp. DIL Variant

-40˚C to +80˚C

MH88437AS-PI Ind. Temp. SM Variant

-40˚C to + 80˚C

MH88437-P

Data Access Arrangement

Advance Information

MH88437-P Advance Information

Figure 2 - Pin Connections

Pin Description

Pin # Name Description

1 NB1 Network Balance 1. External passive components must be connected between this pin and

NB2.

2 NB2 Network Balance 2. External passive components must be connected between this pin and

NB1. 3 VR+ Differential Receive (Input). Analog input from modem/fax chip set. 4 VR- Differential Receive (Input). Analog input from modem/fax chip set. 5VXTransmit (Output). Ground referenced (AGND) output to modem/fax chip set, biased at

+2.0V. 6LCLoop Control (Input). A logic 1 applied to this pin activates internal circuitry which provides

a DC termination across Tip and Ring. This pin is also used for dial pulse application. 7ZALine Impedance. Connect impedance matching components from this pin to Ground

(AGND). 8 AGND Analog Ground. 4-Wire 0V reference connect to mains earth (ground). 9VCCPositive Supply Voltage. +5V.

10 VBIAS Internal Reference Voltage. +2.0V reference voltage. This pin should be decoupled

externally to AGND, typically with a 10µF 6.3V capacitor.

11 LOOP Loop (Output). The output voltage on this pin is proportional to the line voltage across Tip -

Ring, scaled down by a factor of 50.

12,

IC Internal Connection. No connection should be made to this pin externally.

13 RS Ringing Sensitivity. Connecting a link or resistor between this pin and LOOP (pin 11) will

vary the ringing detection sensitivity of the module.

15 LCD Loop Condition Detect (Output). Indicates the status of loop current. 16 RV Ringing Voltage Detect (Output). The R V output indicates the presence of a ringing voltage

applied across the Tip and Ring leads.

17 CL Current Limit. A logic 0 applied to this pin activates internal circuitry which limits the loop

current.

18 NP No Pin. Isolation Barrier, ﬁtted, no pin ﬁtted in this position. 19 NP No Pin. Isolation barrier, no pin ﬁtted in this position

TIP

AGND

RING

VR-

VCC

1 2 3 4 5 6 7 8 9 10 11 12 13 14

28 27 26 25 24 23 22 21 20 19 18 17 16 15

VR+

NB1 NB2

VBIAS

LOOP

VLOOP1 VLOOP2 IC

SC SC

NP NP

LCD

Advance Information MH88437-P

20,23

IC Internal Connection. No connection should be made to this pin externally.

21,22 SC Short Circuit. These two pins should be connected to each other via a 0Ω link.

24 VLOOP2 Loop Voltage Control Node 2. Used to set DC termination characteristics. 25 VLOOP1 Loop Voltage Control Node 1. Used to set DC termination characteristics. 27 RING Ring Lead. Connects to the “Ring” lead of the telephone line. 28 TIP Tip Lead. Connects to the “Tip” lead of the telephone line.

Pin Description (continued)

Pin # Name Description

Functional Description

The device is a Data Access Arrangement (D.A.A.). It is used to correctly terminate a 2-Wire telephone line. It provides a signalling link and a 2-4 Wire line interface between an analog loop and subscriber data transmission equipment, such as Modems, Facsimiles (Fax’s), Remote Meters, Electronic Point of Sale equipment and Set Top Boxes.

Isolation Barrier

The device provides an isolation barrier capable of meeting the supplementary barrier requirements of the international standard IEC 950 and the national variants of this scheme such as EN 60950 for European applications and UL 1950 for North American applications.

External Protection Circuit

An External Protection Circuit assists in preventing damage to the device and the subscriber equipment, due to over-voltage conditions. See Application Note MSAN-154 for recommendations.

Suitable Markets

The MH88437 has features such as programmable line and network balance impedance, programmable DC termination and a supplementary isolation barrier. For countries that do not need to meet the French and German requirements there is a pin for pin compatible device the MH88435.

There are, however, a small number of countries with a 100MΩ leakage requirement that this device does not meet. These are Belgium, Greece, Italy, Luxembourg, Spain and Poland. Although Luxembourg will now accept TBR21 and there are exceptions to the Italian speciﬁcation, in most

applications the MH88437 will comply with Luxembourg and Italian speciﬁcations. For approval in Denmark and Sweden the TRB21 route is recommended.

Approval speciﬁcations are regularly changing and the relevant speciﬁcation should alw ays be consulted before commencing design.

Line Termination

When Loop Control (LC) is at a logic 1, a line termination is applied across Tip and Ring. The device can be considered off-hook and DC loop current will ﬂow. The line termination consists of both a DC line termination and an AC input impedance. It is used to terminate an incoming call, seize the line for an outgoing call, or if it is applied and disconnected at the required rate, can be used to generate dial pulses.

The DC termination resembles approximately 300Ω resistance, which is loop current dependent. Furthermore, it can be programmed to meet different national requirements. For normal operation VLOOP3 should be open circuit and a resistor (R2) should be ﬁtted between VLOOP1 and VLOOP2, as shown in Figure 4.

The approval speciﬁcation will give a DC mask characteristic that the equipment will need to comply to. The DC mask speciﬁes the amount of current the DAA can sink for a given voltage across tip and ring. Graph 1 shows how the voltage across tip and ring varies with different resistors (R2) for a given loop current.

Network Balance

The network balance impedance of the device can be programmed by adding external components By

MH88437-P Advance Information

applying a logic 0 to Pin 17, CL, the loop current will be limited to below 60mA as required in France and the European TBR21 speciﬁcation. For all other countries where current limiting is not required, CL should be set to 1.

The AC input impedance should be set by the user to match the line impedance.

Input Impedance

The MH88437 has a programmable input impedance set by ﬁtting external components between the ZA pin and AGND.

For complex impedances the conﬁguration shown in Figure 4 (below) is most commonly found.

Figure 4 - Complex Impedances

To ﬁnd the external programming components for conﬁguration 4, the following formula should be used:

Zext = [(10 x R1)-1k3]+[(10 x R2)//(C1/10)]

e.g. If the required input impedance = 220Ω + (820Ω/ /115nF), the external network to be connected to ZA will be:

ZA = 900Ω + (8k2Ω//12nF) Where the input impedance (Z) = 600R the equation

can be simpliﬁed to:

ZA = (10 x Z) - 1k3Ω

ZA = 4k7Ω

Note: A table of commonly used impedances can be found in the DAA Application’s document MSAN-154.

Where Zext = external network connected between ZA and AGND and Zint = 1.3kΩ (internal resistance)

between NB1 and NB2. For countries where the balance impedance matches the line impedance, a 16kΩ resistor should be added between NB1 and NB2.

Figure 3 - DC Programming Capability

Iloop=15mA

Iloop=20mA

Iloop=26mA

50 150 250 350 450 550 650 750 850 950

R2(kOhms)

V(t-r)

Advance Information MH88437-P

Ringing Voltage Detection

The sensitivity of the ringing voltage detection circuitry can be adjusted by applying an external resistor (R7, Figure 5) between the RS and LOOP pins. With a short circuit, the threshold sensitivity is ~10Vrms, therefore R7 = 30kΩ x (Desired threshold voltage - 10Vrms).

Example: 300kΩ gives ~20Vrms and 600kΩ 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 OnHook 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 low 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 offhook state. This is to allow the subscriber to make emergency calls.

To detect this state, additional circuitry will be required. Refer to 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 at 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 MH88437 has the ability to transmit analog signals from Tip and Ring through to VX when onhook. This can be used when receiving caller line identiﬁcation information.

Transmit Gain

The Transmit Gain of the MH88437 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 MH88437, 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.

Receive Gain

The Receive Gain of the MH88437 is the gain from the differential signal at VR+ and VR- to the differential signal across Tip and Ring. The internal Receive Gain of the device is ﬁxed as shown in the AC Electrical Characteristics table. For the correct

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