MH88422
the device has an internal cancellation circuit. The
measure of attenuation is Transhybrid Loss (THL).
The Transmit (VX) and Receive (VR) signals are
ground referenced (AGND), and biased to 2.5V. The
device must be in the off-hook condition for
transmission or reception to take place.
Preliminary Information
Characteristics table. For the correct gain, the Input
Impedance of the MH88422 variant used, must match
the specified line impedance.
The input impedance to ground of VR is 47kΩ and this
can be used with an external series resistor to form a
potential divider and reduce the overall gain in the
application.
Example: If R3 = 100kΩ, in Figure 3, the Gain would
reduce by 3.0dB.
Transmit Gain
The Transmit Gain of the MH88422 is the gain from the
differential signal across Tip and Ring to the ground
referenced signal at VX. The internal Transmit Gain of
the device is fixed and depends on the variant as
shown in the AC Electrical Characteristics table. For
the correct gain, the Input Impedance of the MH88422
variant used, must match the specified line
impedance.
By adding an external potential divider to VX, it is
possible to reduce the overall gain in the application.
The output impedance of VX is approximately 10Ω and
the minimum resistance from VX to ground should be
2kΩ.
Example: If R1 = R2 = 2kΩ, in Figure 3, the gain would
reduce by 6.0dB.
Supervisory Features
The device is capable of monitoring the line
conditions across Tip and Ring, this is shown in
Figure 3. The Ringing Voltage Loop Current detect
pin (RVLC), indicates the status of the device. The
RVLC output is at logic 0 when loop current flows,
indicating that the MH88422 is in an off hook state.
When the device is generating dial pulses, the RVLC
pin outputs a TTL pulse at the same rate.
An AC ringing voltage across Tip and Ring will cause
RVLC to output a TTL pulse at double the ringing
frequency with an envelope determined by the
ringing cadence.
Receive Gain
The Receive Gain of the MH88422 is the gain from the
ground referenced signal at VR to the differential
signal across Tip and Ring. The internal Receive Gain
of the device is fixed as shown in the AC Electrical
Mechanical Data
See Figure 10, for details of the mechanical
specification.
MH88422
R2
TIP
26
24
Protection
Circuit
C2
20
18
16
TIP
RLS
VR
TF
RVLC
TXIN
5
LC
VDD
1
AGND
3
7
Ring Voltage & Loop
Current Detect Output
11
VX
R3
R1
C3
Audio
Output
Audio
Input
13
C4
RING
RING
Loop Control Input
Notes:
1) R1, R2: Transmit Gain Resistors
2) R3: Receive Gain Resistor
C1
3) C1: 10µF 6V Tantalum
4) C2: Dummy Ringer Capacitor 250V
5) C3, C4: 10µF AC coupling Capacitors
+
+5V
Figure 3 - Typical Application Circuit
2-16
MITEL [ MITEL NETWORKS CORPORATION ]
