MH88435AD-PI datasheet(6/16 Pages) MITEL

6 / 16 page

MH88435-P

Preliminary Information

2-44

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 47k

Ω at

the VR+ and VR- pins, external series resistors can

be used to reduce the overall gain.

Overall Receive Gain = 0dB + 20log (47k

Ω /

(47k

Ω+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.

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

on-hook.

Therefore,

line

conditions

can

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.

Mechanical Data

See Figure 12, 13 and 14 for details of the

mechanical speciﬁcation.

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