MITEL MH88632 Datasheet

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MH88632

Central Office Interface Circuit

Preliminary Info rm atio n

Features

• Loop star t and g round st art capa bilities

• Transforme rless 2-4 wire conve rsion

• Programmable transmit/receive gain with 0dB defaults

• Programmab le inp ut impe danc e with 60 0Ω an d 900Ω def aults

• Programmable network balance with 600Ω, 900Ω, and AT&T comp rom ise de faul t

• One loop start & two ground start relay drivers

• Line state detec tion out put s

• Forward loop , revers e loop , ring grou nd, ti p ground, rin ging vo ltage

• +5V operati on

• On-hook audio reception (to accommodate ANI)

Applications

Interface to Central Office for:

• PBX

• Key Telephone Sys tem

• Channel bank

•Voice Mail

• Terminal Equip men t

• Digital Lo op Carri er

ISSUE 5 April 1995

Ordering Information

MH88632 40 Pin S IL Pack age

0°C to 70°C

Description

The Mitel MH88632 Central Office Trunk Interface circuit provides a complete audio and signalling link between audio switching equipment and a central office. The functions provided by the MH88632 include 2-4 Wire Hybrid conversion, programmable transmit and receive gains, programmable line impedance and programmable network balance. The device is fabricated using thick film hybrid technology w hich incorporates various tech nologies for optimum circuit design and very high re liability.

XLA XLB XLC XLD

LRC LRD

BRC BRD

GRC GRD

TIPRING

Loop

Termination

Loop Rela y

Driver

Bias Relay

Driver

Ring Ground

Driver

VRLY RGND

VDD

Impedance

Matching

Z600

VEE

2-4 Wire Hybrid

Z900NSN1N2NATT

AGND

Network Balance

RV FL RL

Figure 1 - Functiona l Block Dia gram

Status

Detection

RG TG

Receive

Gain

Transmit

Gain

RX GRX1 GRX0

GTX1 GTX0

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MH88632 Preliminary Information

TIP

RING

XLA XLB XLC XLD

GRD

IC RGND VRLY

LRD

BRD

LRC

BRC

GRC

AGND

NATT

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Z900

Z1 Z2

GTX0

GTX1

GRX0

GRX1

IC Z600

VEE

VDD

Figure 2 - Pin Connections

Pin Description

Pin # Name

1TIPTip Lead. Connects to the “Tip” or “Ring” lead of Central Office. 2 RING Ring Lead. Connects to the “Ring” or “Tip” lead of the Central Office.

Description

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

3XLALoop Relay Contac t A. Connects to XLB through the loop relay (K1) contacts when the

relay is activated. Act ivat es internal active term ina tion circuitr y. 4XLBLoop Relay Contac t B. See XLA for description. 5XLCL oo p Relay Contac t C. Connects to XLD through the loop relay (K1) contacts when the

relay is activated. Act ivat es internal active term ina tion circuitr y. 6XLDL oo p Relay Contac t D. See XLC for description 7ICInternal Connection.T his pin is internally connected and m ust be left open. 8GRD

Ground Relay Lead Relay Drive (Output). Connects to the Ground Ring Lead Relay Coil,

used for Ground Start applicat ions. A logic low activates the rela y. An internal clamp diode

from VRLY to GND is provided. 9ICInternal Connection. This pin is internally connect ed and must be left open.

10 IC Internal Connection. This pin is internally connected and must be left open. 11 RGND R e lay Gr ou nd. Retu rn path for relay supply volta ge. 12 VRLY Relay Positiv e Suppl y Voltage. Normally +5V. Connects to the relay coil and the relay

supply voltage

13 LRD

14 BRD

Loop Relay Drive (Output). Connects to the Bias Relay coil. A logic low activates the

relay. An internal clamp diode from VR LY to LRD

is provided.

Bias Relay Driv e (Outpu t). Connect s to the Bias Relay coil, used for Ground start

applications only. A logic low activates the relay. An internal clamp diode from VRLY to BRD

is provided.

15 LRC Loop Relay Control (Input). A logic high activates the Loop Relay Drive output (LRD

Loop Relay activates inte rnal cir cuitry which provides a DC terminati on a cross Tip and

Ring. Used for line seizure and dial pulsing.

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). The

Preliminary Information MH88632

Pin Description (Continued)

Pin # Name

16 BRC Bias Relay Con trol (Inp ut). A logic high activates the Loop Relay Drive output (BRD),

used for Ground start application s only. This input should be connected to logic high when not used.

17 GRC Ground Ring Lead Relay Control (Input). A logic low activates the Ground Ring Lead

Relay Drive output (GRD

connected to logic high when not used. 18 AGND Analog Ground. 4-Wire ground. Normally connected to System Ground. 19 NATT Networ k Balance AT+T Node. Connects to N1 for a network balance impedance of AT&T

compromise (350Ω + 1k Ω // 210nF); the device’s input impedance must be set to 600Ω.

This node is active only when NS is at logic high. This node should be left open circuit when

not used. 20 N1 Network Balance Node 1 (Input). 0.1 times the impedance between pins N1 and N2 must

match the device’s input impedance, while 0.1 times the impedance between pins N1 and

AGND is the device’s network balance impedance. This node is active only when NS is at

logic high. This node may be terminate d when not used (i.e., NS at logic low). 21 N2 Network Balance Node 2 (Output). See N1 for description. 22 Z900 L ine Imp edan ce 900Ω Node. Co nnects to Z1 for a line impedance of 900 Ω. This node

should be left open circuit when not used. 23 Z1 Line Impedance Node 1 (Input). 0.1 times the times the impedance between pins Z1 and

Z2 is the device’s line impedance. This node must always be connected.

), used for Ground Start applications only. This input should be

Descrip tio n

24 Z2 Line Impedance Nod e 2 (Outpu t ). 0.1 time s the times the impedance betwee n pins Z1

and Z2 is the device’s line impedance. This node should be left open circuit when not used. 25 TX Transmit (output). 4-Wire ground (AGND) reference d audio output. 26 RX Receive (Input). 4-Wire ground (AGND) referenced audio input. 27 GTX0 Transmit Gain Node 0. Connects to GTX1 for 0dB transmit gain. 28 GTX1 Transmit Gain Node 1. Connects to a resistor to AGND for transmit gain adjustment. 29 GRX0 Receive Gain Node 0. Connects to GRX1 for 0dB gain. 30 GRX1 Receive Gain Node 1. Connects to a resistor to AGND for receive gain adjustment. 31 IC Internal Connection. This pin is internally connected and must be left open. 32 Z600 Line Impedance 600

pin should be left open circuit when not used. 33 NS Network Balance Setting (Input. The logic level at NS selects the network balance

impedance. A logic 0 enables an internal balance equivalen t to the input impedance (Zin).

While a logic 1 enables an external balance 0.1 times the impedance between pins N1 and

AGND balanced to 0.1 times the impedance betwe en pins N1 and N2. The impeda nce

between N1 and N2 must be equivalent to 10 times the input impedance (Zi n). 34 TG

35 RL

Tip Lead Ground Detect (Outpu t ). A logic low output indicat es that the Tip lead is at

ground (AGND) potent ial .

Ring Loop Detect (Output). In the on-hook state, a logic low output indicates that reverse

loop battery is present. In the off-hook state, a logic low out put ind icates that reverse loop

current is present. Reverse loop refers to the Tip lead negative with respect to the Ring

lead.

Ω Node (Output). Connects to Z1 for a line impedance of 600Ω. This

RV Ri ng Voltage Detect (Output). A logic low indicates that ringing voltage is across the Tip

and Ring leads. Note that this output toggles at the ringing cadence and not at the ringing

frequency.

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MH88632 Preliminary Information

Pin Description (Continued)

Pin # Name

39 VEE N e gati ve Supp ly Voltage. -5V dc. 40 VDD Positive Su pp ly Voltage. +5V dc.

FL Forward Loop Detect (Output). In the on hook state, a logic low output indicate s that

forward loop battery is present. In the off-hook state, a logic low output indicates that forward loop current is present. Forward loop refers to the Ring Lead negative with respect to the Tip lead.

RG Ring Lead Grou nd Detec t (Ou tpu t). A logi c low indicates that t he Ring lead is at ground

(AGND ) potential.

Functional Description

The MH88632 is a COIC (Central Office Interface Circuit) used to interface to Central Office 2-Wire Analog Trunks. The COIC provides both Loop start and Ground start interface capabilities.

Approvals

FCC part 68, DOC CS-03, UL 1459, CAN/CSA 22.2 No.225-M90 are all system (i.e., connectors, power supply, cabinet, etc.) requirements. Since the MH88632 is a component and not a system, it cannot be approved as a stand alone part by these standards bodies. However, when installed into a properly designed system, the MH88632 has been designed to meet the CO Trunk Interface requirements of FCC, DOC, UL and CSA, and thus enabling the complete system to be approved by these standards bodies.

To meet the regulatory high voltage requirements, an external protection circuit is required. The protection circuit shown in Figure 9 is matched to the MH88632 and ensures than they meet the high voltage requirements of FCC, DOC, CSA and UL when installed in a properly designed system.

Descrip tio n

200Ω and 275Ω. An external relay is used to activate internal circuitry which switches the termination in and out of the loop. This is used for both seizing the line as well as generating dial pulses.

Supervision Features

The supervision circuitry provides the signalling status outputs. The system controlling the COIC, monitors these logic outputs. The supervision circuitry is capable of detecting ringing voltage, both forward and reverse loop battery and loop current, and both grounded tip lead and grounded ring lead.

a) Su pervision Features RV

Detect Output)

The RV logic low when ringing voltage is detected. This detector includes a ringing filter which ensures that the output toggles at the ringing cadence and not at the ringing frequency. Typically, this output goes low 50ms after ringing voltage is applied and remains low for 50ms after ringing voltage is removed.

b) Supervision Features FL & RL (Forward Loop

(Ringing Voltage Detect) output provides a

and Revers e Loo p Dete ct Out put).

(Ring Voltage

Products are designed in accordance with meeting the above requirements; however, full conformance to these standards is dependent upon the application in which the hybrid is being used, and therefore, approvals are the responsibility of the customer and Mitel will not have tested the product to meet the above standards.

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 LRC (Loop Start Relay Control) input. the termination is similar to a DC resistance between

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The FL low when either forward loop battery or forward loo p current is detected (ring lead voltage negative with respect to ring lead). The RL output provides a logic low when either reverse loop battery or reverse loop current is detected (tip lead voltage negative with re spect to ring lead ).

See Table 5 for Loop Battery and Current Status Outputs.

(Forward Loop Detect) out put provides a logic

(Reverse Loop Detect)

Preliminary Information MH88632

c) Supervision Features TG & RG (Tip Ground

and Ring Ground Detect Output)

The TG logic low when the tip lead is at ground (AGND) potential. The RG provides a logic low when the Ring lead is at ground (AGND) potential.

See Table 6 for Loop Ground Status Outputs.

(Tip Lead Ground Detect) output provides a

(Ring Lead Ground Detect) output

Ground Start Signalling Features

For Ground Start signalling, relay K2 and resistors R1 and R2, and relay K3 and resistor R3 are required (S ee Figure 8). Activation of K2 is controlled by the logic signal at the BRC (Bias Relay Control) input while activation of K3 is controlled by the logic signal at the GRC (Ground Relay Control) input.

K2 is used to engage the bias resistors while K3 is used to ground the right lead; this is used in ground start applications for signalling to the central office.

Typical Ground Star t Signalling Protocol

Refer to Figure 8 for Typical LS-GS Application Circuit.

In the idle state, the system (e.g., PBX control card) provides a logic high to the BRC input. This activates the COIC’s second internal relay driver which activates relay K2. Both contacts of relay K2 close, which connect the -48VDC supply to Tip (tip lead) and Ring (ring lead) through bias resistors R1 and R2.

Depending on which Ground Start protocol is used, initiating a Ground start call to the central office can be performed by the following sequence of events.

The system provides a logic low to the GRC input. this activates the COIC’s third internal relay driver which activates relay K3. The contacts of relay K3 close, which connects the ring lead to ground through a current lim i ti ng resistor R3.

The Central Office reconizes the ring ground condition and responds by grounding the tip lead.

The COIC senses the grounded Tip and switched the TG

(Tip Lead Ground Detect) output to a logic low.

The system then applies a logic high to the LRC (Loop Relay Control) input. This activates the COIC’s first internal relay driver which activates relay K1. Both contact s th e r elay K1 close, w hic h ac tiva te s th e COIC’s internal circuitry resulting in an active line termination across Tip and Ring. The system then provides a logic low to the BRC input. This deactivates the COIC’s second internal relay driver which deactivates K2. Both contacts of relay K2 open, which disconnect the bias from Tip and Ring. The system then provides a logic high to the GRC input. This deactivates the COIC’s third internal relay driver which deactivates relay K3. The contact of relay K3 opens. which disconnects the grounded ring lead. The voice link is now established.

Receiving a Ground Start call from central office is performed similarly. The central office can signal the COIC by either grounding the tip lead or by gro und i ng t he ri n g lea d .

Hybrid

The 2-4 Wire Hybrid circuit separates the balanced full duplex signal at Tip and Ring of the telephone line into receive and transmit ground referenced signals at Rx (Receive) and TX (Transmit) of the COIC. The hybrid also prevents the input signal at RX from appearing at TX. The degree to which the Hybrid minimises the contribution of the RX signal at the TX output is specified as transhybrid loss. For maximizing transhybrid loss, see the Network

Balance section.

The 4-Wire side can be interfaced to a filter/codec such as the Mitel MT896X, for use in digital voice switched systems.

Line Impedance

The MH88632’s Tip-Ring impedance (Zin) can be set to 600Ω, 900Ω or to a user selectable value. Thus, Zin can be set to any international requirements. The connection to Z1 determines the input impedance. With Z1 connected to Z600, the line impedance is set to 600Ω. With Z1 connected to Z900, the line impedance is set to 900Ω. A user defined impedance can be selected which is 0.1 times the impedance between Z1 and Z2. For example, with 2200Ω in series with 11.5nF in parallel with 8200Ω, all between Z1 and Z2, the devices line impedance will be 220Ω in series with 115nF in parallel with 820Ω. See Table 3 and Figures 4 & 5.

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MH88632 Preliminary Information

Stability

The part will be stable with an AC load over the range 0.5 Z

The range of loads that can be simulated by the MH88632 is extensive including those which are purely resistive and complex in nature. For loads with a low or zero series resistance additional measures need to be taken to maintain stability which involves simulating with a larger series resistance and adjusting other components accordingly.

Examples:

Sweden

is synthesised on the MH88632 by 1.5kΩ in series with a parallel combination of 3nF and 7.4kΩ.

Norway

combination of 820Ω and 110nF. This is synthesized on the MH88632 by 1.5kΩ in series with a parallel combination of 12nF and 7.8kΩ.

Italy:

Load is 750Ω in parallel with 18nF. This is synthesised on the MH88632 by 1.5kΩ in series with a parallel combination of 2nF and 6kΩ.

<Load < 2 x Zin.

: Load is 900Ω in a parallel with 30nF. This

: Load is 120Ω in series with a parallel

Networ k Balan ce

Transhybrid loss is maximized when the line termination impedance and COIC network balance are matched. The MH88632’s network balance impedance can be set to Z 210nf) or to a user Selectable value. Thus, the network balance impedance can be set to any international requirement. A logic level control input NS selects the balance mode. With NS at logic low, an internal network balance impedance is matched to the line impedance (Z user defined network balance impedance is selected which is 0.1 times the impedance between N1 and AGND. For example, with 2200Ω in series with

11.5nF in parallel with 8200Ω, all between N1and AGND, and NS at logic high, the devices network balance impedance in 220Ω in series with 115nF in parallel with 820Ω, the impedance between N1 and N2 must be equivalent to 10 times the input impedance (Z AT&T network balance impedance can be selected by connecting NATT to N1; in this case, no ad dit ion a l network is required between N1 and N2. See Table 4 and Figures 6 & 7.

). In addition, with NS at logic high, an

, AT&T (350Ω+1kΩ //

). With NS at logic high, a

TIP-RING Drive Circuit

The audio input ground referenced signal at RX is converted to a balanced output signal at Tip and Ring. The Tip-Ring Drive Circuit is optimised for good 2-Wire longitudinal balance.

TIP-RING Receive Circuit

The differential audio signal at Tip and Ring is converted to a ground referenced audio signal at the TX output. Th is circuit operates with or witho ut loop current; signal reception with no loop current is required for on-hook reception enabling the detection of ANI (Automatic Number Identification) signals.

Programmable Transmit and Receive Gain

Transmit gain (Tip-Ring to TX) and receive Gain (RX to Tip-Ring) are programmed by connecting external resistors (RRX and RTX) from GRX1 to AGND and from GTX1 to AGND as indicated in Figure 3 and Tables 1 and 2. The programmable gain range is from -12dB to +6dB; this wide range will accommodate any loss plan. Alternatively, the default Receive Gain of 0dB and Transmit Gain of 0dB can be obtained by connecting GRX0 to GRX1 and GTX0 to GTX1. In addition, a Receive Gain of +6dB and Transmit Gain of +6dB can be obtained by not connecting resistors RRX and RTX. For correct gain programming, the MH88632’s Tip-Ring impedance (Z impedance. For optimum performance, resistor RRX should be physically located as close as possible to the GRX1 input pin.

) must match the line termination

ANI (Automatic Nu mber I denti fica tion)

ANI provides the called party with calling party telephone number identification. The central office utilizes the voice path of a regular loop-start telephone line when the COIC (subscriber’s terminal) is i n th e on -hoo k st ate. Th e ce ntr al off ice send s th e ANI information (data transmission typically of an FSK signal of 1200Hz and 2200Hz) typically 600ms after the first ring ing b u r s t.

The COIC outputs this FSK signal at the TX output.

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