MH88632 Ver la hoja de datos (PDF) - Mitel Networks
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MH88632 Datasheet PDF : 18 Pages
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MH88632
Preliminary Information
Stability
The part will be stable with an AC load over the
range 0.5 Zin <Load < 2 x Zin.
The range of loads that can be simulated by the
MH88632 is extensive including those which are
purely resistive and complex in nature. For loads
with a low or zero series resistance additional
measures need to be taken to maintain stability
which involves simulating with a larger series
resistance and adjusting other components
accordingly.
Examples:
Sweden: Load is 900Ω in a parallel with 30nF. This
is synthesised on the MH88632 by 1.5kΩ in series
with a parallel combination of 3nF and 7.4kΩ.
Norway: Load is 120Ω in series with a parallel
combination of 820Ω and 110nF. This is synthesized
on the MH88632 by 1.5kΩ in series with a parallel
combination of 12nF and 7.8kΩ.
Italy: Load is 750Ω in parallel with 18nF. This is
synthesised on the MH88632 by 1.5kΩ in series with
a parallel combination of 2nF and 6kΩ.
Network Balance
Transhybrid loss is maximized when the line
termination impedance and COIC network balance
are matched. The MH88632’s network balance
impedance can be set to Zin, AT&T (350Ω+1kΩ //
210nf) or to a user Selectable value. Thus, the
network balance impedance can be set to any
international requirement. A logic level control input
NS selects the balance mode. With NS at logic low,
an internal network balance impedance is matched
to the line impedance (Zin). With NS at logic high, a
user defined network balance impedance is selected
which is 0.1 times the impedance between N1 and
AGND. For example, with 2200Ω in series with
11.5nF in parallel with 8200Ω, all between N1and
AGND, and NS at logic high, the devices network
balance impedance in 220Ω in series with 115nF in
parallel with 820Ω, the impedance between N1 and
N2 must be equivalent to 10 times the input
impedance (Zin). In addition, with NS at logic high, an
AT&T network balance impedance can be selected
by connecting NATT to N1; in this case, no additional
network is required between N1 and N2. See
Table 4 and Figures 6 & 7.
TIP-RING Drive Circuit
The audio input ground referenced signal at RX is
converted to a balanced output signal at Tip and
Ring. The Tip-Ring Drive Circuit is optimised for
good 2-Wire longitudinal balance.
TIP-RING Receive Circuit
The differential audio signal at Tip and Ring is
converted to a ground referenced audio signal at the
TX output. This circuit operates with or without loop
current; signal reception with no loop current is
required for on-hook reception enabling the detection
of ANI (Automatic Number Identification) signals.
Programmable Transmit and Receive
Gain
Transmit gain (Tip-Ring to TX) and receive Gain (RX
to Tip-Ring) are programmed by connecting external
resistors (RRX and RTX) from GRX1 to AGND and
from GTX1 to AGND as indicated in Figure 3 and
Tables 1 and 2. The programmable gain range is
from -12dB to +6dB; this wide range will
accommodate any loss plan. Alternatively, the
default Receive Gain of 0dB and Transmit Gain of
0dB can be obtained by connecting GRX0 to GRX1
and GTX0 to GTX1. In addition, a Receive Gain of
+6dB and Transmit Gain of +6dB can be obtained by
not connecting resistors RRX and RTX. For correct
gain programming, the MH88632’s Tip-Ring
impedance (Zin) must match the line termination
impedance. For optimum performance, resistor RRX
should be physically located as close as possible to
the GRX1 input pin.
ANI (Automatic Number Identification)
ANI provides the called party with calling party
telephone number identification. The central office
utilizes the voice path of a regular loop-start
telephone line when the COIC (subscriber’s terminal)
is in the on-hook state. The central office sends the
ANI information (data transmission typically of an
FSK signal of 1200Hz and 2200Hz) typically 600ms
after the first ringing burst.
The COIC outputs this FSK signal at the TX output.
2-240
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