®
MH88600
Global SLIC
Preliminary Information
Features
•
•
•
•
•
•
•
•
•
•
•
•
Programmable line impedance matching
Internal complex impedance networks
Transformerless 2-4 wire conversion
Programmable transmit/receive gain
Accommodates worldwide transmission
standards
Operates with a wide range of battery voltages
Adjustable constant current battery feed
Overvoltage and short circuit protection
Switch hook and ground button detection
Ring trip filter and relay driver
Low power consumption
High power dissipation capability during fault
conditions
MH88600
ISSUE 7
April 1995
Ordering Information
40 Pin DIL Hybrid
0°C to 70°C
Description
The MH88600 is a SLIC (Subscriber Line Interface
Circuit) which provides all of the BORSCH functions
of Battery Feed, Overvoltage Protection, Ringing
Feed, Line Supervision and 2-4 Wire Hybrid
conversion. In addition, the device matches the
many different line impedances specified by
regulatory authorities of around the world.
Applications
Line interface for:
• PABXs
•
•
•
Control Systems
Key Telephone Systems
Central Office Equipment
VREF
TF1
TF2
Tip Drive
Constant
Current
Battery Feed
Impedance Matching Network
PG2
2-4 Wire
Hybrid
Circuit
PG4
Gain Adjust
TX
PG3
PG1
LCA
ZN14 ZN13.................ZN8
ZN7.....................ZN1 ZN0
TIP
RING
Over Voltage &
Short Circuit
Protection
RF1
Ring Trip Filter
Ring Drive
Line Supervision
Relay Driver
RF2
Vbat
EGB
SHK
Figure 1 - Functional Block Diagram
2-83
GNDBat
GNDA
VRR
VDD
VEE
RC
RD
MH88600
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
ZN14
ZN13
ZN12
ZN11
ZN10
ZN9
ZN8
ZN7
ZN6
ZN5
ZN4
ZN3
ZN2
ZN1
TX
PG3
PG1
PG2
PG4
ZN0
Preliminary Information
VBat
RF1
RF2
RING
TIP
IC
GNDBat
TF2
TF1
GNDA
VEE
VDD
VRR
RC
RD
LCA
SHK
EGB
VRef
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Figure 2 - Pin Connections
Pin Description
Pin #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
V
Bat
RF1
RF2
Name
No pin at this location.
Battery Supply Voltage (Negative).
Description
Ring Feed (1):
Connect to relay contact. See Figures 6 & 7.
Ring Feed (2).
Connect to relay contact. See Figures 6 & 7.
Connects to the “Ring” or “B” lead of the telephone line.
Connects to the “Tip” or “A” lead of the telephone line.
Internal Connection.
Battery Supply Ground (Positive):
Connect to System Ground
Tip Feed (2).
Connect to TF1 for unbalanced ringing, see Figure 6. Connect to relay
contact for balanced ringing, see Figure 7.
Tip Feed (1).
Connect to TF2 for unbalanced ringing, see Figure 6. Connect to relay
contact for balanced ringing, see Figure 7.
Analog Ground:
Normally connected to System Ground.
Negative Power Supply Voltage:
Normally -5V.
Positive Power Supply Voltage:
Normally +5V.
Ringing Relay Clamp Diode:
Connect to relay coil and to relay supply voltage
(Positive). For +5V relay, connect to VDD.
Ring Control (Input):
A logic high will activate the Ring Relay Drive if SHK is high.
Ring Relay Drive (Output).
Connect to relay coil. A logic low will activate the relay by
sinking current from VRR through the relay coil.
Loop Current Adjust (Input):
Loop current is proportional to the voltage at this input.
Normally connected to VRef
Switch Hook Detect (Output):
A logic low indicates an off-hook condition.
Earth Ground Button (Output):
A logic low indicates a grounded Ring lead condition.
Voltage Reference (Output):
Normally connected to LCA for default loop current.
RING
TIP
I/C
GND
Bat
TF2
TF1
GNDA
V
EE
V
DD
V
RR
RC
RD
LCA
SHK
EGB
V
Ref
2-84
Preliminary Information
Pin Description (Continued)
Pin #
21
22
23
24
25
26
27
Name
ZN0
MH88600
Description
Impedance Node 0.
Connect to external network for impedance (Z
in
) setting. See Table
2 and Figure 8.
Programming 4 (Input).
Used for programmable gain and for default gain. Used as 4-
Wire Receive Input for default gain. See Table 3 and Figure 4 and 5.
Programming 2 (Input).
Used for programmable gain. Used with resistor for 4-Wire
Receive Input. See Table 3 and Figure 4.
Programming 1 (Input).
Used for programmable gain. See Table 3 and Figure 4.
Programming 3 (Input).
Used for programmable gain and for default gain. See Table 3
and Figure 4 and 5.
4-Wire Transmit Output:
Impedance Node 1:
Connect to other Impedance Nodes for impedance (Z
in
) setting,
see Table 1. Or, connect to external network for impedance (Z
in
) setting, see Table 2 and
Figure 8.
Impedance Node 2:
Connect to other impedances Nodes for impedance (Z
in
) setting.
See Table 1.
Impedance Node 3:
As per ZN2. See Table 1.
Impedance Node 4:
As per ZN2. See Table 1
Impedance Node 5:
As per ZN2. See Table 1
Impedance Node 6:
As per ZN2. See Table 1
Impedance Node 7:
As per ZN2. See Table 1
Impedance Node 8:
As per ZN2. See Table 1
Impedance Node 9:
As per ZN2. See Table 1
Impedance Node 10:
As per ZN2. See Table 1
Impedance Node 11:
As per ZN2. See Table 1
Impedance Node 12:
As per ZN2. See Table 1
Impedance Node 13:
As per ZN2. See Table 1
Impedance Node 14:
Connect to external network for impedance (Z
in
) setting. See
Table 2 and Figure 8.
.
PG4
PG2
PG1
PG3
TX
ZN1
28
29
30
31
32
33
34
35
36
37
38
39
40
ZN2
ZN3
ZN4
ZN5
ZN6
ZN7
ZN8
ZN9
ZN10
ZN11
ZN12
ZN13
ZN14
2-85
MH88600
Functional Description
The BORSH Functions
The MH88600 performs all of the BORSH functions;
Battery Feed, Overvoltage Protection, Ringing,
Supervision and Hybrid.
Battery Feed
The MH88600 provides the loop with constant DC
current to power the telephone set. The voltage
(negative) applied at the LCA pin determines the
magnitude of the lop current.
I
Loop
= 3.731 x VLCA mA (±2mA)
Either the internal (V
Ref
) or an external negative
voltage reference may be used to set the loop
current.
Overvoltage Protection
The MH88600 is protected from short term (20ms)
transients (+250V) between Tip and Ring, Tip and
ground, and Ring and Ground. However, additional
protection circuitry may be needed depending on the
regulatory requirements which must be met.
Normally, simple external shunt protection as shown
in Figures 6,7 and 8 is all that is required.
Ringing
The MH88600 has the capability to accommodate
both balanced and unbalanced ringing sources.
Refer to Figure 7 for the Balanced Ringing Circuit
and Figure 6 for the Unbalanced Ringing Circuit.
Supervision
The MH88600 is capable of detecting both Ground
Button and Switch Hook conditions. The Ground
Button detection (a logic low at the EGB output)
operates when an imbalance in Tip and Ring DC
current exceeds an internal threshold level caused
by a grounded Ring Lead. Use of the EGB output is
restricted to the off-hook condition of the telephone.
The Switch Hook detection operates (a logic low at
the SHK output) when the DC loop current exceeds
an internal threshold level.
The Ring Trip Detection Circuit prevents false off-
hook detection due to the current associated with the
AC ringing voltage and also due to the large current
transients when the ring voltage is switched in and
out. In addition, the circuit prevents connection of the
ringing source during off-hook conditions.
2-86
Preliminary Information
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
SLIC. The Hybrid also prevents the input signal at
RX from appearing at TX. The degree to which the
Hybrid prevents the RX signal from appearing at TX
is specified at transhybrid loss.
Tip-Ring Drive Circuit
The audio input ground referenced signal at RX is
converted to a balanced output signal at Tip and
Ring. The output signal consists of the audio signal
superimposed on the DC Battery Feed Constant
Current. The Tip-Ring Drive Circuit is optimised for
good 2-Wire longitudinal balance.
Short Circuit Protection
The MH88600 is protected from long term (infinite)
short circuit conditions occurring between Tip and
Ring, Tip and Ground, Ring and Ground, and Ring
and Battery. The current is limited to the same value
as the Constant Current Battery Feed.
Programmable Line Impedance
The MH88600’s Tip-Ring (Z
in
) impedance can be
matched to the different impedances specified by
different telephone administrations worldwide. This
is accomplished by either linking specific pins as
specified in Table 1, or by adding external
components as shown in Figure 8 and Table 2.
Programmable Transmit & Receive Gain
Transmit gain (TX to Tip-Ring) and Receive Gain
(Tip-Ring to RX) can be programmed by connecting
external resistors as indicated in Figure 4 and Table
3. Alternatively, the default Receive Gain of -4d Band
Transmit Gain of +4dB can be obtained by
connecting pins as shown in figure 5 and Table3.
Note that RX is not a pin on the SLIC. The RX
terminal will be either PG4 or the connection to the
receive gain programming resistor RRX shown in
Figure 4 and Figure 5.
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