MH88520-1
Ringing
The relay drive circuit switches ringing onto Ring
Feed (Fig. 7). The diode is present to suppress
voltage transients during relay switching caused by
the inductive coils of the relay. Ringing voltage
included ac ringing (90V
RMS
typically) and DC line
feed voltage (-24V typically).
Preliminary Information
Line Impedance
The MH88520-1’s Tip-Ring (Zin) impedance is fixed
at the German complex impedance. For correct SLIC
impedance, JUNC must be appropriately terminated.
See AC Electrical Characteristics.
Transmit and Receive Gain
Transmit Gain (JUNC to Tip-Ring) and Receive Gain
(Tip-Ring to JUNC) are fixed (See AC Electrical
Characteristics). For correct gain, the SLIC input
impedance must match theline impedance and
JUNC must be appropriately terminated.
Line Feed/Ring Feed Circuit
The line feed circuit provides loop current and the
ability to apply ringing onto Tip and Ring. The
impedance from Ring Feed to GND is 600Ω dc
(although for ac it is optimised for a German complex
impedance) which gives the loop current as:
Voltage at Ring Feed pin
Telephone Impedance + 600
Amps
Digital Applications
The 2-wire junctor output can be converted to a
4-wire circuit using the MH88524 (2-4 wire
converter). This 4 wire circuit can be interfaced to a
filter/codec to use in digital voice switched systems.
Alternatively the MH88600/MH88612, digital ONS
SLIC can be used.
The positive supply for the line feed circuit is VDD
though the loop current is determined from Ring
Feed and GND.
TYPICAL
RETURN
LOSS
(dB)
10
20
30
40
50
60
550
600
650
700
750
800
850
900
950
LOAD IMPEDANCE ON JUNCTOR (Ω)
Figure 4 - Return Loss VS Junctor Load Impedance
2-66
MITEL [ MITEL NETWORKS CORPORATION ]
