MH88435AS-PI datasheet(4/16 Pages) MITEL

4 / 16 page

MH88435-P

Preliminary Information

2-42

Input Impedance

The MH88435 has a programmable input impedance

set by ﬁtting external components between the ZA

pin and AGND.

For complex impedances the conﬁguration shown in

Figure 4 is most commonly found.

Figure 4 - Complex Impedances

To ﬁnd the external programming components for

conﬁguration 4, the following formula should be

used:

Zext = [(10 x R1)-1k3]+ [10 x R2)//(C1/10)]

e.g. If the required input impedance = 220

Ω +

(820

Ω//115nF), the external network to be connected

to ZA will be:

Zext = 900

Ω + (8k2Ω//12nF)

Where the input impedance (Z) = 600R the equation

can be simpliﬁed to:

Zext = (10 x Z) - 1k3

Ω

Zext = 4k7

Ω

Note: A table of commonly used impedances can be

found in the DAA Application’s document MSAN-154.

Zext = external network connected between ZA and

AGND, Zint = 1.3k

Ω (internal resistance).

Network Balance

The network balance impedance of the device can

be programmed by adding external components

between NB1 and NB2. For countries where the

balance impedance matches the line impedance, a

15k

Ω resistor should be added between NB1 and

NB2.

Ringing Voltage Detection

The sensitivity of the ringing voltage detection

circuitry can be adjusted by applying an external

resistor between the RS and LOOP pins. With a

short circuit, the threshold sensitivity is ~10Vrms R7

can be calculated using the equation:

Iloop=26mA

Iloop=20mA

Iloop=15mA

R2(kOhms)

200

600

1000

1400

1800

2200

2600

3000

3400

3800

Figure 3 - DC Programming Capabilities

(V(t-r)

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