MH88435-P
Data Access Arrangement
Preliminary Information
Features
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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
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.
Applications
Interface to Central Office or PABX line for:
• FAX/Modem (including software modems)
• Electronic Point of Sale
• Security System
• Telemetry
• Set Top Boxes
Isolation Barrier
VCC
VBIAS
AGND
LC
TIP
RING
Input Buffer
&
Line Termination
Isolation
Analog
Buffer
VR+
VR-
NB1
NB2
THL cancellation
and line
impedance
matching circuit
VX
ZA
RV
LCD
LOOP
RS
Network Connections
User Connections
Opto-
Isolation
Logic Input
Buffer
Isolation
VLOOP1
VLOOP2
Isolation
Analog
Buffer
Ring & Loop
Buffer
Figure 1 - Functional Block Diagram
2-39
MH88435-P
NB1
NB2
VR+
VR-
VX
LC
ZA
AGND
VCC
VBIAS
LOOP
IC
RS
IC
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
TIP
RING
IC
VLOOP1
VLOOP2
IC
SC
SC
IC
NP
NP
IC
RV
LCD
Preliminary Information
Figure 2 - Pin Connections
Pin Description
Pin #
1
2
3
4
5
6
Name
NB1
NB2
VR+
VR-
VX
LC
Description
Network Balance 1.
External passive components must be connected between this pin
and NB2.
Network Balance 2.
External passive components must be connected between this pin
and NB1.
Differential Receive (Input).
Analog input from modem/fax chip set.
Differential Receive (Input).
Analog input from modem/fax chip set.
Transmit (Output).
Ground referenced (AGND) output to modem/fax chip set, biased at
+2.0V.
Loop 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.
Line Impedance.
Connect impedance matching components from this pin to Ground
(AGND).
Analog Ground.
4-Wire ground. Connect to earth.
Positive Supply Voltage.
+5V.
Internal Reference Voltage.
+2.0V reference voltage. This pin should be decoupled
externally to AGND, typically with a 10
µF
6.3V capacitor
.
Loop (Output).
The output voltage on this pin is proportional to the line voltage across Tip
- Ring, scaled down by a factor of 50.
Internal Connection.
No connection should be made to this pin externally.
7
8
9
10
11
12,
14,
17,
20,
23,
26
13
15
16
ZA
AGND
V
CC
VBIAS
LOOP
IC
RS
LCD
RV
Ringing Sensitivity.
Connecting a link or resistor between this pin and LOOP (pin 11) will
vary the ringing detection sensitivity of the module.
Loop Condition Detect (Output).
Indicates the status of loop current.
Ringing Voltage Detect (Output).
The RV output indicates the presence of a ringing
voltage applied across the Tip and Ring leads.
2-40
Preliminary Information
Pin Description (continued)
18,
19
21,
22
24
25
27
28
NP
SC
VLOOP2
VLOOP1
RING
TIP
No Pin.
Isolation barrier, no pin fitted in this position.
MH88435-P
Short Circuit.
These two pins should be connected to each other via a 0Ω
link.
Loop Voltage Control Node 2.
Used to set DC termination characteristics.
Loop Voltage Control Node 1.
Used to set DC termination characteristics.
Ring Lead.
Connects to the “Ring” lead of the telephone line.
Tip Lead.
Connects to the “Tip” lead of the telephone line.
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.
France’s current limit specification and Germany’s
dial pulse requirements are met by the MH88437.
This device is pin for pin compatible with the
MH88435.
Approval specifications are regularly changing and
the relevant specification should always be consulted
before commencing design.
Line Termination
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 and is classified as a Telecom
Network Voltage (TNV) circuit.
When Loop Control (LC) is at a logic 1, a line
termination is applied across Tip and Ring. The
device is 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 is approximately 300Ω
resistance, which is loop current dependent. It can
be programmed to meet different national
requirements. For normal operation Pin 22 and Pin
21 should be linked, and a resistor (R2) should be
fitted between VLOOP1 and VLOOP2 as shown in
Figure 5.
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 source for a given voltage across tip and
ring. Figure 3 shows how the voltage across tip and
ring varies with different resistors (R2) for a given
loop current.
The AC input impedance should be set by the user to
match the line impedance.
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 MH88435 has features such as programmable
input
and
network
balance
impedance,
programmable DC termination and a supplementary
isolation barrier that makes it ideal for use
throughout the world.
There are a small number of countries with a 100MΩ
leakage requirement that this device does not meet.
These are Belgium, Greece, Italy, Luxembourg and
Spain.
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MH88435-P
30
Preliminary Information
25
20
(V(t-r)
Iloop=26mA
Iloop=20mA
Iloop=15mA
15
10
5
0
200
600
1000
1400
1800
2200
2600
3000
3400
3800
R2(kOhms)
Figure 3 - DC Programming Capabilities
Input Impedance
The MH88435 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 is most commonly found.
ZA
R1
R2
Where the input impedance (Z) = 600R the equation
can be simplified to:
Zext = (10 x Z) - 1k3Ω
Zext = 4k7Ω
Note: A table of commonly used impedances can be
found in the DAA Application’s document MSAN-154.
Zext = external network connected between ZA and
AGND, Zint = 1.3kΩ (internal resistance).
C1
Network Balance
The network balance impedance of the device can
be programmed by adding external components
between NB1 and NB2. For countries where the
balance impedance matches the line impedance, a
15kΩ resistor should be added between NB1 and
NB2.
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)]
Ringing Voltage Detection
e.g. If the required input impedance = 220Ω +
(820Ω//115nF), the external network to be connected
to ZA will be:
Zext = 900Ω
+
(8k2Ω//12nF)
The sensitivity of the ringing voltage detection
circuitry can be adjusted by applying an external
resistor between the RS and LOOP pins. With a
short circuit, the threshold sensitivity is ~10Vrms R7
can be calculated using the equation:
2-42
Preliminary Information
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.
MH88435-P
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.
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.
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.
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