MH88622
Off-Hook and Dial Pulse Detection
The SHK pin goes low when e DC loop current
exceeds a specified level. The threshold level is
internally set by the bias voltage of the switch hook
detect circuit.
Dial pulse can be detected by monitoring the
interruption rate at the SHK pin. These dial pulses may
need to be debounced by the systems software.
Preliminary Information
High Voltage Capability
Inherent in the thick film process is the ability of the
thick film process dielectric strengths of greater than
1000 VAC or 1500 VDC. The thick film process
allows easy integration of surface mount
components such as the high voltage bi-polar power
transistor line drivers. This allows for simpler, less
elaborate and less expensive protection circuitry
required to handle high voltage transients and fault
conditions caused by lightening, induced voltages
and power line crossing.
Ring Trip Detection
The interface permits detection of an Off-Hook
condition during ringing. If the subscriber set goes
Off-Hook when the ringing signal has been applied,
the DC loop current flow will be detected within
approx. 100msecs and the SHK output will go low.
The ringing is automatically disabled by the internal
hardware.
On Hook Transmission
The MH88622 provides for on-hook transmission
which supports features such as Automatic Number
identifications (ANI).
Loop Length
The MH88622 can accommodate loop length of up to
2000Ω
minimum
(including
the
subscriber
equipment).
Longitudinal Balance
Precision laser trimming of resistors in the hybrids
ensures good overall longitudinal balance.
The interface circuitry can operate in the presence of
induced longitudinal currents of up to 40mA rms at
60Hz.
T
PROTECTION
T
PTC
RESISTOR
5 Ohms
TISP2290
or
P2702AB
R
PTC
RESISTOR
5 Ohms
R
Figure 4 - Typical Protection Circuit
2-180
MITEL [ MITEL NETWORKS CORPORATION ]
