Datasheet MH88631-1, MH88631-2 Datasheet (MITEL)



MH88631

Central Office Interface (LS/GS)

Preliminary Info rm atio n

Features

• Transformerle ss 2-4 w ire conv ersi on

• Line state dete ction outp uts

• - forward current

• - reverse current

• - ring ground

• - tip ground

• - ringing voltage

• Programmable audio transmit and receive gain

• Loop start or gro und s tart term inati on

• Selectable 600Ω or AT&T compromise ba lanc e
network

• -1 version: 20Hz Ringing Voltage

• -2 version: 50Hz Ringing Voltage

Applications

• PBX

• Channel b ank

• Intercom

• Key System

ISSUE 4 April 1995

Ordering Information

MH88631 -1 40 Pin S IL Pa ckag e
MH88631 -2 40 Pin S IL Pa ckag e

0°C to 70°C

Description

The Mitel MH88631-1, 2 Central Office Trunk
Interface circuit provides a complete audio and
signalling link between audio switching equipment
and a central office. The loop seize circuitry is
controlled by an external input to provide either a
loop start of ground start termination. The device is
fabricated using thick film ceramic technology to
achieve high density circuit design.

T
R

VTR+

VTR­RXIN­RXIN+

RG FC

Signal Detection

Active

Termination

QB QE XA XB XC VDD

RV

Circuitry

RC

TG

LPGND RINGND

Ground

Network
Balance

Figure 1 - Functiona l Block Dia gram

Ring

VEE

Audio Section

RXOUT

VCC+

VCC- AGND

Driver 1

Driver 2

Circuitry

(2-4 Wire)

TXIN+ TXIN-

Relay

Relay

RC1
RD1

RGND
CD

RD2
RC2

NETBAL
GSX

VX
VR
GSR

2-225

MH88631 Preliminary Information

LPGND

VDD

RINGND

T
R

VTR-

VTR+

XC

XA

QE
AGND
RXIN+

RXIN-

VEE

TG
RC
RV

FC
RG
QB

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

XB

VEE

VDD

RXOUT

VCC+

GSR

TXIN-

VCC­TXIN+
AGND

VR

VX

RGND

GSX

RC1

NETBAL

RD1

CD
RD2
RC2

Figure 2 - Pin Connections

Pin Description

Pin #

1LPGNDLoop Ground is the system ground reference with respect to -48V.
2VDDPositive Po wer Supply (+5V).

Name Description

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

3 RINGND

Ring Ground (Input). For Ground Start Trunk only a logic low input will enable the trunk
circuit to ground the Ring lead through a low resistance (390Ω). This is a signal to the C.O.

that the interface is seizing the line.
4TTip (Inp u t). Normall y connects to the “Tip” lead of the C.O.
5RRing (Input). Normally connects to the “Ring” lead of the C.O.
6 VTR- Connects to the TXIN+ (Pin 29) via an external capacitor (C1).
7 VTR+ Connects to the collector of an external transistor (Q1) and TXIN- (Pin 27) via an external

capacitor (C4)
8 XC External relay contact (K1) connecti on from XB (Pin 21), activates by loop seize control

input (RC1).
9 XA E xternal relay con tact (K1) connecti on from VTR+ (Pi n 7), activated by loop sei ze control

input (RC1).

10 QE Connects to the emitter of an external transistor (Q1).
11 AGND Analog Grou nd.
12 RXIN+ Differential Receive (Input). Connects to analog ground via an external capacitor (C2).
13 RXIN- Differential Receive (Input). Connects to RXOUT (Pin 24) via an external capacitor (C3).
14 VEE Negative Po wer S up ply. (-5V).

15 TG

Tip Lead Ground Detect (Ou tpu t). Active low.

16 RC Reverse Loop Current Detect (Outpu t). Active low .
17 RV Ringing Voltage Detect (Output). Active low.
18 FC

Forward Loop Curre nt Detect (Outpu t). Active low

19 RG Ring Lead detect (Output). Active low.
20 QB Connects to the base of an external transistor (Q1).

2-226

Preliminary Information MH88631

Pin Description (Continued)

Pin #

21 XB External relay contact (K1) connection from XC (Pin 8), activated by loop seize control input

22 VEE Negative Po wer S up ply. (-5V).
23 VDD Po siti ve Power Sup ply. (+5V)
24 RXOUT Audio receive signal (outpu t) tothe RX IN- (Pi n 13), via an external decoupling capacitor

25 VCC+ Positive analog Power S up ply Voltage. (+12V).
26 GSR Gain Setting Rec eive (Input). Normally used to set the receive gain with an external

27 TXIN- Transmit (Input). Differe ntial audio signa l from VTR- (Pin 6), via an external capacitor

28 VCC- Negative Analog Power S upp ly Voltage. (-12V).
29 T XIN+ Transmit (Input). Differential audio signal from VTR- (Pin 6), via an external decoupling

30 AG ND An al og Gr ound.
31 VR Audio Receive (In pu t). The four-wire audio signal input to the interface .
32 VX Audio Transmit (Output). The four-wire audio signal output from the interfa ce.

Name Description

(RC1).

(C3).

resistor connected to RXOUT (Pin 24).

(C4).

capacitor (C1).

33 RGND Relay Grou nd.
34 GSX Gain Setti ng Transmit (Input). Normally used to set the transmit gain with an external

resistor connected to VX (Pin 32).

35 RC1 R e lay Co ntro l 1 (Input). A logic high will activate the relay (K1) to provid e loop seize

across Tip and Ring.

36

37

38

39 RD2 R e lay Dri ver 2 (Output). Op en collect or sinks current when RC2 is high. Diode clam p

40 RC2 R e lay Dri ver 2 (In put). A logic high will activate the relay (K2) to provide proper biasing to

NETBAL Network Balance (Input). When there is no connection (open), the network is balanced at

600Ω. When the pin is grounded, the network is balanced at AT&T compromise.

RD1 Relay Dri ver 1 (Outp ut). Open collect or sinks curren t when RC1 is high. Diode clamp

protecte d.

CD Clamping Diode. Normally connects to the po sitive supply voltage.

protecte d.

the Tip and Ring. This input control is used for Ground Start Trunk only.

2-227

MH88631 Preliminary Information

Functional Description

The MH88631-1, 2, is a Central Office Loop Start
and/or Ground start analog Trunk interface circuit
providing a complete audio and signalling link to the
Central Office.

The trunk interface circuit performs transformerless
2 to 4 wire conversion, between the 2-wire telephone
loop and the 4 wire transmit and receive pairs of a
voice switching system. The 4-wire connection can
be interfaced to a filter/ codec, such as the MT896X,
for use in a digital voice switched system.

Voiceband analog signals, coming for the C.O.,
applied differentially across Tip and Ring, pass
through a bridge rectifier and appear at VTR+ and
VTR- where they are actively terminated. Refer to
Fig. 3 - Application Circuit. External capacitors C1
and C4 couple the incoming signals into the
balanced input of the Transmit audio circuitry via
TXIN+ and TXIN-. The transmit gain is adjusted by
feedback resistor R4. For best performance R4
should be physically located as close as possible to
the GSX pin. The gain adjusted transmit signal
appears at the Vx output pin.

Relay K1 is the loop seize which applies active line
termination and also provides biasing of the current
modulator circuitry. Activating and deactivating K1
provides dial pulsing. Q1 is the current modulator
output transistor, referred to as the loop driver
transistor.

compromise network consisting of 350Ω plus 1kΩ
shunted by a 0.21µF capacitor. This is typical of
North American C.O. connections.

The Tip and Ring also provide the balanced input to
the signal detection circuitry which generates the
signalling status outputs TG

For Ground Start signalling, relay K2 and resistor R1
and R2, are required. Activation of K2 is controlled
by the relay control logic input signal, RC2. In the
idle state, K2 is closed connecting the -48 VDC
supply Tip and Ring through biasing resistors R1 and
R2. Upon detection of TG
pulls RC1 low, closing K1, then pulls RC2 low which
opens K2 to remove the -48 volts supply from Tip
and Ring.

In the Ground Start signalling environment, initiating
a call to the C.O. is performed by the following
sequence of events. The system provides a logic low
on the ring ground input pin of the interface. This
activates the circuitry which grounds the ring lead
through a current limiting resistance. The C.O.
recognizes the ground condition and connects the tip
lead to ground. The interface senses this condition
and the tip lead ground detect output switches to a
logic low. The system then applies active line
termination by closing K1 using RC1 and opens K2
using RC2. A call from the C.O. can be performed
similarly. The C.O. can signal to the interface by
pulling either Tip or Ring to ground potential, or by
applying ringing voltage to the Ring lead.

, RC, RV, FC and RG.

or RG, the system then

Outgoing analog signals from the system are
provided to the interface at the VR input where they
enter an amplifier section with the gain controlled by
the selection of the Rx gain feedback resistor R3.
For best performance, R3 should be physically
located as close as possible to the GSR pin. The
output of the amplifier, RXOUT, is coupled to RXIN-,
the current modu lato r cir cuitry, via C3. The bala nced
input to the current modula tor is completed with the
connection of C2 from RXIN+ to ground.
Transmission to the C.O. is accomplished by
modulating the loop with the outgoing analog
signals. To ensure that the transmitted signals are
not coupled to the receive circuitry, transhybrid loss
is maximised. The impedance matching, performed
by the balance network reduces power loss and
signal reflections. The network balance input,
NETBAL, of the interface’s 2-wire to 4-wire convertor
circuitry provides selection of a 600Ω balance, used
when feeding channel banks or when performing
external tests on the trunk circuit, or the AT&T
compromise. When the NETBAL input pin is
grounded, the interface balance against the AT&T

Signal Detection Circuitry

The signal detection circuitry provides the signalling
status outputs. The system, controlling the
interfaces, monitors these active low logic outputs.
RV

is the Ringing Voltage detect outputs. When the
C.O. applies ringing voltage to the termination, the
trunk interface provides a 50ms debounced output at
RV during the ringing burst period. This output will
remain low for approximately 50ms after C.O.
removes the ringing Voltage. Ringing voltage above
40 VRMS at 20Hz will be detected.

TG is the Tip lead Ground detect output and RG is
the Ring lead Ground detect output. The TG
outputs provides a means of determining call original
or other hand shaking functions. The high
impedance detection circuitry of the interface will
detect both Tip and Ring Ground voltages above
approximately -15.3V of true ground.

RC is the Reverse Loop Current detect output and
FC is th e F orward Loop C u rr en t de te c t o u tp ut .

and RG

2-228

Preliminary Information MH88631

The RC and FC outputs of the interfaces are used to
determine the p olarity of the Tip and Ring pair which
the C.O. uses for signalling during the active (off-hook)
state of the interf ace. When the loop is closed by the
interface, the trunk is in the normal or unreversed
state. Some C.O.’s may reverse the polarity of Tip and
Ring, to indicate the talking state. The interface will
detect this condition and RC

will output a low level.

External Circuitry Requirements

The loop seize circuit is completed with the addition
of external components Q1, C5, R5 and K1.

K1, a DPST reed relay, is activated by relay control
signal RC1. When the loop seizure is required, K1 is
closed and the interface applies active termination
across Tip and Ring. The relay should have a 0.5
amp contact capability and 12 VDC operation with a
typical 500Ω coil resistance. To prevent back EMF
from damaging the relay drive transistor, (caused by
the collapsing field of the inductive coil of the relay) a
snubbing diode is provided on the hybrid and
therefore not required externally. C5 and R5 provide
relay contact noise filtering and transient noise
suppression necessary for clamping inductive spikes
created when the loop is closed during line seizure
or dial pulsing.

and Ring inputs of the interface, following by metal
oxide varistors from Tip and Ground, Ring to Ground
and Tip to Ring.

Components List (for Fi gure 3)

R1*, R2* = 30. 9k Ω, ± 1% 1/4W
R4 = Transmit Gain Adjust Resistor

= 301.5 E3x Gain VX - 100 E3

VTR

Typical Value = 200kΩ, ± 1% 1/4W

R3 = Receive Gain Adjust Resistor

= 523.2 E3 x Gain VTR

VR

Typical Value = 505kΩ, ± 1%, 1/4W
R5 = 510Ω, ± 5% ,
R6 = 10kΩ, ± 5%,
C1, C2, C3 , C 4 = 0 .2 2 µ F, ± 10%, 200V
C5 = 0.1µ F, ± 5%, 250V
C6 = 1.0µ F, ± 5%, 250V
Q1 = 2N5657, NPN 350V, 0.5A, 20W
K1, K2 = 2A Reed R e l a y, E/M 12V

2 Form C Di p

*Note: required for Ground Start applications, not
required for Loop start applications.

1
1

/4W
/4W

Q1 provides current drive for the active termination,
controlling the loop current flow of the current
modulator circuitry. Selection of a suitable transistor
for Q1 is made based on worst case conditions
which include fault conditions. A 350 volt, or higher,
rating for Q1 is necessary to meet high voltage
requirements. The Tip and Ring input protection
varistors limit any high voltage spikes to
approximately 300 volts. Under worst case
conditions Q1 must be able to handle close to
100mA of collector current and dissipate two watts
continuously. During pulse dialling, current spikes
are generated due to the inductive nature of the loop.
A 0.5 amp continuous connector current rating is
therefore recommended to provide a safe margin.

K2, R1 and R2 are required only for Ground Start
applications. K2 is the same type of relay as K 1 and
is activated by RC2. Once again the snubbing diode
is provided on the hybrid. R1 and R2 provide the

-48V biasing the signalling (on-hook) state.
R6 and C6 constitute the Dummy Ringer required for

the LS/GS trunk. These components are also part of
the 600Ω input impedance.

Protection circuitry on the Tip and Ring inputs may
be required depending upon the trunk interface
application. For maximum protection it is
recommended to place fuses in series with the Tip

2-229

MH88631 Preliminary Information

Absolute Maximum Ratings*

Parameter Sym Min Max Units

-0.3

-0.6

+18.0

-55 +125 °C

V

V

V

CC +

DD ­EE -

CC

GNDD
GNDD

-GNDA

- GNDA

STG

1 DC Supply Voltage V

2 Storage Temperature T

* Exceeding these values ma y cause perm anen t dama ge. Functi onal operati on und er these cond ition s is not implied.

Recommended Operating Conditions

Parameter Sym Typ* Min Max Units Comments

1 Operating Supply Voltage V

2 Operating Current I

V
V

V
V

I
I
I

DD
EE

CC+

CC

Bat

DD
DD
DD
DD

3 Power Consumption P
4 Operating Temperature T

* Typical figures are at 25° C with nominal + 5V supplies for design aid only.

OP

4.75

-5.25

11.4

-11.4

C

5.0

-5.0

12.0

12.0

-48

5.25

-4.75

12.6

-12.6

6.0

-6.0

8.0

-8.0

mA
mA
mA
mA

265 mW

V
V
V
V
V

RINGND

070°C

DC Electrical Characteristics‡

Characteris tics Sym Min Typ* Max Units Test Conditions

+6.0
+0.3

+18.0

V
V
V
V

high

1 Input High Volt age RC1, RC2

V

IH

RINGND

2 Input High Current RC1, RC2

I

IH

RINGND

3 Input Low Voltage RC1, RC2

V

IL

RINGND

4 Input Low Current RC1, RC2

I

IL

RINGND

‡ 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 .

2.7

4.5

2.5 5.0

-100

0.7 V

1.0

1.1

V
V

mA

µA

µA

mA

Control Inputs State Table

Parameter Active Idle

1 RC1 L ogic high Logic Low
2 RC2 Logic High Logic Low
3 RINGND Logic Low Logic High
4 NETBAL

AT&T compromise network
(350Ω + 1k Ω/ 0.2µ F)
600Ω network

Open (no connection)

AGND

2-230

Preliminary Information MH88631

AC Electrical Characteristics

Characteristics Sym Min Typ* Max Units Test Conditions

1 Ringing Voltage VR 40 90 130 V
2 Ringing Frequency -1 version

20

rms

Hz

Voltage range 40

-120Vrms

-2 version

50

Hz

Voltage range 35

-120Vrms
3 Operating Loop Current IL 18 70 m A
4 Off-Hook DC Resistance RT 300 Ω @18mA
5 Operating Loop Resistance RL 2300 Ω @18mA
6 On-Hook Leakage Current 3 µΑ RINGND = 5.0Vdc
7 Ring Ground Sink Current IRG 100 mΑ -48VDC with 200Ω in

series on Ring lead

8 Tip and Ring AC Impedance 600 Ω with 1.0 kΩ + 1.0µF in

parallel with Tip and
Ring

9 Longitudinal Balance

metallic to longit udina l
longitudinal to metallic

10 Return Loss Trunk to Line 20

11 Transhybrid Loss (single freque ncy)

THL 18.5

into 600Ω

12 Transhybrid Loss (single frequency)

THL 18

into AT&T Compromise

13 Frequency respo nse (Output relative

to 1kHz, VTR/VR and VX/ VT R)

60
40
58
53

26
30

-0.15

-0.10

-0.10

-0.15

34
30

20

0.05

0.05

0.05

0.05

dB
dB
dB
dB

dB
dB
dB

dB
dB
dB

dB
dB

dB
dB
dB
dB

200-1000Hz
1000-4000Hz
200-1020Hz
1020-3020Hz

200-500Hz
500-1000Hz
1000-340Hz

200Hz
1000Hz
3000Hz

200-1000Hz
1000-4000Hz

200Hz
300Hz
3000Hz
3400Hz

See Note 1
14 Idle channel noise 8 dB rnco C-Message
15 Power Supply rejecti on ratio PSR

40 dB

R

16 Analog signal overload level

(adjustable gain)

* Typical figure are at 25°C with nom inal ±5V supplie s and are for desig n aid only
Note 1: Input 0dBm at VTR, or input 0.0775Vrms at VR. TR=600Ω Termination .

6 dBm 1kHz,0dBm

= 0.775Vrms into 600Ω

DC Electrical Characteristics

Characteristics Sym Min Typ* Max Units Test Conditions

1 Output High Voltage

, RC, RV, FC , R G ) 4.75 V No Load on output

(TG

2 Output High Current

, RC, RV, FC , R G )0.17mAV

(TG

3 Output Low Voltage

, RC, RV, FC , R G ) -0.30 V No Load on output

(TG

4 Output Low Sink Current

, RC, RV, FC , R G ) -0.40 mA VOL=-0.4Vdc

(TG

* Typical figure are at 25°C with nom inal ±5V supplie s and are for desig n aid only

=-2.7Vdc

OH

2-231

MH88631 Preliminary Information

TIP

RING

LIGHTNING

PROTECTION

DUMMY RINGER

R1

K2A

-48V BATTERY

+12V

MH88631-1, -2

4

T

R6
C6

5

R

R2

11,30

AGND

K2B

-48V RETURN

Loop Current Setting

K2

K1

1

LPGND

33

RGND

40

RC2

39

RD2

38

CD

37

RD1

35

RC1

16

RC

17

RV

18

FC

19

RG

15

TG

V

V

DD

2,23 22,14 25 28

EE

RXOUT

NETBAL

RINGND

V

CC+

VTR­TXIN+
RXIN+

RXIN-

GSR

XB

XC

XA

TXIN

VTR+

QB
QE

VR

VX

GSX

V

CC-

12

13

26

10

36

31
32

34

29

24

21

8

9
27

20

3

C1

6

C2

C3

R3

K1A

K1B
C4

7

Q1

R4

C5
R5

2-232

+5V

-5V

+12V

-12V

Figure 3 - Application Circuit

Preliminary Information MH88631

Side View

0.002

0.010 +

0.05)

(0.25 +

Notes:

1)Not to scale

2)Dimensions in inches).

3) (Dimensions in millimetres).
*Dimensio ns to centre of pin &

tolerance non ac cumulati ve.

0.140 Max
(3.6 Max)

0.14 Max

(3.6 Max)

0.60 Max

(15.25 Ma x )

0.05 +

1234 3940

*

0.01

0.5)

(1.3 +

0.05 +
(1.3 +

0.05)

Figure 4 - Mechanical Data

4.00 + 0.03
(102 +

1.0)

0.18 +

***

0.02

0.020 +
(0.51 +

0.05

0.13)

0.100 +
(2.54 +

0.13)

(4.6 +

0.10

0.02

0.5)

2-233

MH88631 Preliminary Information

Notes:

2-234