Preliminary Information
Pin Description (continued)
Pin #
22
23
24
25
26
27
28
Name
X2
C1
SHK
RLYC
RLYD
GND
VEE
Description
MT91600
Gain Node 2.
Networks, either resistive or complex, are connected between this node,
VR and GND to set the Network Balance Impedance for the SLIC.
A filter capacitor for ring trip is connected between this pin and GND.
Switch Hook (Output).
This pin indicates the line state of the subscribers telephone.
The output can also be used for dial pulse monitoring. SHK is high in off-hook state.
Relay Control (Input).
An active high on this pin will switch RLYD low.
Inverted Output of RLYC.
It is used to drive the bipolar transistor that drives the relay
(see Figure 5.)
Ground. Return path for +5V and -5V.
This should also be connected back to the
return path for the loop battery, LGND and relay drive ground RLYGND.
Negative supply rail, -5V.
4W to 2W gain:
Gain 4 - 2 = 20*Log [0.891 * (R14 / R15)]
Functional Description
The MT91600 is the analog SLIC for use in a 4 Wire
switched system. The SLIC performs all of the
normal interface functions between the CODEC or
switching system and the analog telephone line such
as 2W to 4W conversion, constant current feed,
ringing and ring trip detection, current limiting, switch
hook indication and line and network balance
impedance
setting
using
minimal
external
components.
Refer to Figure
designation.
5
for
MT91600
components
Impedance Programming
The MT91600 allows the designer to set the device’s
impedance across TIP and RING, (Z
TR
), and
network balance impedance, (Z
NB
), separately with
external low cost components.
For a resistive load, the impedance (Z
TR
) is set by
R11 and R18. For a complex load, the impedance
(Z
TR
) is set by R11, R18, R19 & C8 (see Figure 5.)
The network balance, (Z
NB
), is set by R16, R17 & C3
(see Figure 5.)
The network balance impedance should
calculated once the 2W - 4W gain has been set.
be
2 Wire to 4 Wire Conversion
The hybrid performs 2 wire to 4 wire conversion by
taking the 4 wire signal from an analog switch or
voice CODEC, a.c. coupled to V
R
, and converting it
to a 2 wire differential signal at tip and ring. The 2
wire signal applied to tip and ring by the telephone is
converted to a 4 wire signal, a.c. coupled to Vx which
is the output from the SLIC to the analog switch or
voice CODEC.
Line Impedance
For optimum performance, the characteristic
impedance of the line, (Z
o
), and the device’s
impedance across TIP and RING, (Z
TR
), should
match. Therefore:
Z
o
= Z
TR
The relationship between Z
o
and the components
that set Z
TR
is given by the formula:
Z
o
/ ( R1+R2) = kZ
o
/ R11
where kZ
o
= Z
LZ
Z
LZ
= R18, for a resistive load.
Z
LZ
= [R18 + (R19 // C8)], for a complex load.
3
Gain Control
It is possible to set the Transmit and Receive gains
by the selection of the appropriate external
components.
The gains can be calculated by the formulae:
2W to 4W gain:
Gain 2 - 4 = 20*Log [ R13 / R12]
MITEL [ MITEL NETWORKS CORPORATION ]
