MH88422-3 datasheet(4/14 Pages) MITEL

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MH88422

Preliminary Information

2-16

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

the

off-hook

condition

for

transmission or reception to take place.

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 10

Ω and

the minimum resistance from VX to ground should be

Ω.

Example: If R1 = R2 = 2k

Ω, in Figure 3, the gain would

reduce by 6.0dB.

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

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 47k

Ω 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 = 100k

Ω, in Figure 3, the Gain would

reduce by 3.0dB.

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.

Mechanical Data

See Figure 10, for details of the mechanical

speciﬁcation.

Figure 3 - Typical Application Circuit

TIP

RLS

TXIN

RING

RVLC

AGND

VDD

TIP

RING

+5V

Audio

Input

Audio

Ring Voltage & Loop

Current Detect Output

Loop Control Input

MH88422

Protection

Circuit

Output

Notes:

1) R1, R2: Transmit Gain Resistors

2) R3: Receive Gain Resistor

3) C1: 10

µF 6V Tantalum

4) C2: Dummy Ringer Capacitor 250V

5) C3, C4: 10

µF AC coupling Capacitors

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