MH88437 查看數據表（PDF） - Mitel Networks

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MH88437

Data Access Arrangement

Mitel Networks 

MH88437-P

Advance Information

40

35

30

25

V(t-r)

20

15

10

Iloop=15mA

Iloop=20mA

Iloop=26mA

5

0

50

150

250

350

450

550

650

750

850

950

R2(kOhms)

Figure 3 - DC Programming Capability

applying a logic 0 to Pin 17, CL, the loop current will

be limited to below 60mA as required in France and

the European TBR21 specification. For all other

countries where current limiting is not required, CL

should be set to 1.

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)]

The AC input impedance should be set by the user to

match the line impedance.

Input Impedance

The MH88437 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 (below) is most commonly found.

e.g. If the required input impedance = 220Ω + (820Ω/

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

will be:

ZA = 900Ω + (8k2Ω//12nF)

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

can be simplified to:

ZA = (10 x Z) - 1k3Ω

ZA = 4k7Ω

R1

R2

C1

Figure 4 - Complex Impedances

Note: A table of commonly used impedances can be

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

Where Zext = external network connected between

ZA and AGND and Zint = 1.3kΩ (internal resistance)

between NB1 and NB2. For countries where the

balance impedance matches the line impedance, a

16kΩ resistor should be added between NB1 and

NB2.

4

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