MT8870 Mitel Networks Corporation, MT8870 Datasheet - Page 5

• Manufacturer Part Number: MT8870
• Description: ISO2-CMOS Integrated DTMF Receiver
• Manufacturer: Mitel Networks Corporation

Power-down and Inhibit Mode
A logic high applied to pin 6 (PWDN) will power down
the device to minimize the power consumption in a
standby mode. It stops the oscillator and the
functions of the filters.
Inhibit mode is enabled by a logic high input to the
pin 5 (INH). It inhibits the detection of tones
representing characters A, B, C, and D. The output
code will remain the same as the previous detected
code (see Table 1).
Differential Input Configuration
The input arrangement of the MT8870D/MT8870D-1
provides a differential-input operational amplifier as
well as a bias source (V
inputs at mid-rail. Provision is made for connection of
a feedback resistor to the op-amp output (GS) for
adjustment of gain. In a single-ended configuration,
the input pins are connected as shown in Figure 10
with the op-amp connected for unity gain and V
biasing the input at
differential
adjustment of gain with the feedback resistor R
Crystal Oscillator
The internal clock circuit is completed with the
addition of an external 3.579545 MHz crystal and is
normally connected as shown in Figure 10 (Single-
Ended Input Configuration). However, it is possible
to configure several MT8870D/MT8870D-1 devices
employing only a single oscillator crystal. The
oscillator output of the first device in the chain is
coupled through a 30 pF capacitor to the oscillator
input (OSC1) of the next device. Subsequent devices
are connected in a similar fashion. Refer to Figure 7
for
unbalanced loading are not a concern with the
arrangement
capacitors are not required.
details.
configuration,
shown,
The
1
problems
/
Ref
2
i.e.,
V
) which is used to bias the
DD
. Figure 6 shows the
which
precision
associated
permits
balancing
5
.
with
the
Ref
ISO
2
-CMOS
Table 2. Recommended Resonator Specifications
Note: Qm=quality factor of RLC model, i.e., 1/2
Parameter
Differential Input Amplifier
C
R
R
C
C
1
1
2
R
VOLTAGE GAIN (A
INPUT IMPEDANCE
(Z
2
1
=C
=R
=60k , R
Figure 6 - Differential Input Configuration
3
INDIFF
OSC1
OSC2
=
Qm
R1
C1
C0
L1
2
4
=10 nF
=R
f
R
R
R
R
2
Figure 7 - Oscillator Connection
1
4
5
2
) = 2
+R
=100 k
R
R
3
MT8870D/MT8870D-1
5
=37.5 k
5
3
X-tal
C
R
1
v
2
+
diff)=
R
Ohms
IN+
IN-
Unit
2
C
mH
pF
pF
1
%
R
c
-
All resistors are 1% tolerance.
All capacitors are 5% tolerance.
R
R
5
5
1
OSC2
OSC1
2
V
Ref
GS
MT8870D/MT8870D-1
C=30 pF
X-tal=3.579545 MHz
To OSC1 of next
MT8870D/
MT8870D-1
Resonator
+
-
10.752
37.915
896.37
±0.2%
4.984
.432
R1C1.
4-15