
MT88E43B
Preliminary Information
62
Figure 9 - Application Circuit
IN+
IN-
GS
V
Ref
CAP
TRIGin
TRIGRC
TRIGout
MODE
OSCin
OSCout
V
SS
V
DD
St/GT
ESt
StD
INT
DR
DATA
DCLK
FSKen
PWDN
IC
MT88E43B
CD
(FSK Interface Mode 0 selected)
Vdd
= To microcontroller
= From microcontroller
1
TIP / A
RING / B
Vdd
Vdd
Vdd
5
6
464K
499K, 5%
499K, 5%
200K
5%
5%
150K
5%
100nF
5%
100nF
5%
22nF
5%
22nF
5%
100nF
220nF
C
TISP4180,
TISP5180,
TPA150A12 or
TPB150B12
Vdd
100K
20%
NOTE: Resistors must have 1% tolerance and capacitors have 20%
tolerance unless otherwise specified.
: Crystal is 3.579545MHz, 0.1% frequency tolerance.
: For BT application C=0.1
μ
F
±
5%, R
3
=422k
±
1%, R
2
=422k
±
1%
:
For applications where CAS speech immunity is required (e.g. CIDCW)
C=0.1
μ
F
±
5%, R
3
=825k
±
1%, R
2
=226k
±
1%
1N4003
1N4003
1N4003
1N4003
Vdd
1N914
1N914
1N914
1N914
1N914
R
3
R
2
R
1
R
1
: R
1
= 430K, R
4
= 34K for V
DD
= 5V
±
10% (See Figure 10)
: R
1
= 620K, R
4
= 63K4 for V
DD
= 3V
±
10% (See Figure 10)
R
4
R
4
Application Circuits
The circuits shown in Figures 9 and 11 are
application circuits for the MT88E43B. As supply
voltage (V
DD
) is decreased, the threshold of the
device’s tone and FSK detectors will be reduced.
Therefore, to meet the BT or Bellcore tone reject
level requirements the gain of the input opamp
should be reduced according to the graph in Figure
10. For example when V
DD
=5V (+/- 10%), R
1
should
equal 430k
and R
4
should equal 34k
; and if
V
DD
=3V (+/- 10%) R
1
should equal 620k
and R
4
should equal 63.4k
. Resistors R
1
and R
4
are shown
in Figures 9 and 11.
The circuit shown in Figure 9 illustrates the use of the
MT88E43B in a proprietary system that doesn’t need to
meet FCC, DOC, and UL approvals. It should be noted
that if glitches on the Tip/Ring interface are of sufficient
amplitude, the circuit will falsely detect these signals as
ringing or line reversal.
The circuit shown in Figure 11 will provide common
mode rejection of signals received by the ringing circuit.
This circuit should pass safety related tests specified by
FCC Part 68, DOC CS-03, UL 1459, and CSA C22.2.
These safety tests will simulate high voltage faults that
may occur on the line. The circuit provides isolation
from these high voltage faults via R1 and the 12.1k
resistors as well as the 22nF & 330nF capacitors. IRC
manufactures a resistor (part number GS3) that should
be used for R1. This resistor is a 3W, 5%, 1kV power
resistor. The 12k1 resistor is manufactured by IRC (part
number FA8425F). This resistor is a 1.5W, 5%,
fuseable type resistor. The 22nF and 330nF capacitors
have a 400V rating.
See the application note "MSAN-164: Applications of
the MT8843 Calling Number Identification Circuit 2" for
information on designing the MT88E43B into CID and
CIDCW systems.