MH88435-P
Receive Gain
The Receive Gain of the MH88435 is the gain from
the differential signal at VR+ and VR- to the
differential signal across Tip and Ring. The internal
Receive 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.
With an internal series input resistance of 47kΩ at
the VR+ and VR- pins, external series resistors can
be used to reduce the overall gain.
Overall Receive Gain = 0dB + 20log (47kΩ /
(47kΩ+R5)).
For differential applications R6 must be equal to R5
in Figure 5.
Example: If R5 = R6 = 47k in Figure 5, the overall
gain would reduce by 6.0dB.
Preliminary Information
Mechanical Data
See Figure 12, 13 and 14 for details of the
mechanical specification.
Supervisory Features
The device is capable of monitoring the line
conditions across Tip and Ring, this is shown in
Figure 5. The Loop Condition Detect pin (LCD),
indicates the status of the line. The LCD output is at
logic 1 when loop current flows, indicating that the
MH88435 is in an off-hook state. LCD will also go
high if a parallel phone goes off-hook while the DAA
is on-hook. Therefore, line conditions can be
determined with the LC and the LCD pins.
The LOOP pin output voltage, VLoop, is proportional
to the line voltage across Tip and Ring, V (t-r),
scaled down by a factor of 50 and offset by VBias
which is approximately 2V. With the aid of a simple
external detector the LC, LCD and LOOP pins can
be used to generate the signals necessary for
parallel phone operation with a Set Top Box. Refer to
MSAN-154.
If Tip is more positive than ring VLoop < VBias
If Tip is more negative than ring VLoop > VBias
V (t-r)
≈
(VLoop - VBias) * 50
When the device is generating dial pulses, the LCD
pin outputs TTL pulses at the same rate. The LCD
output will also pulse if a parallel phone is used to
pulse dial and also when ringing voltage is present at
Tip and Ring.
2-44
MITEL [ MITEL NETWORKS CORPORATION ]
