MITEL MH88400

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