MH88625 View Datasheet(PDF) - Mitel Networks

Part Name

Description

View to exact match

MH88625

DID/OPS Subscriber line interface circuit (SLIC) for on/off premise PBX line cards, DID line cards and central office cards.

Mitel Networks 

Preliminary Information

MH88625

ILoop (mA)

70

60

50

40

Constant

Current Region

30

Constant

Voltage

Region

20

10

0

1kΩ

2kΩ

Graph 1 - ILoop/RLoop Characteristics

RLoop (Ω)

Two wire Port Termination Impedance

The AC termination impedance of 600 or 900Ω, of the

2W port, is set using active feedback paths to give

the desired relationship between the line voltage and

the line current. The loop current is sensed

differentially across the two feed resistors and

converted to a single ended signal. This signal is fed

back to the Tip/Ring driver circuitry such that

impedance in the feedback path gets reflected to the

two wire port. The MH88625’s Tip-Ring impedance

(Zin) can be set to 600Ω, 900Ω or to a user selectable

value. Thus, Zin can be set to any international

requirement. The connection to Z1 determines the

input impedance. With Z1 connected to Z600, the line

impedance is set to 600Ω. With Z1 connected to

Z900, the line impedance is set to 900Ω. A user

defined impedance can be selected which is 0.1

times the impedance between Z1 and Z2. For

example, with 2200Ω in series with 11.5nF in parallel

with 8200Ω, all between Z1 and Z2, the devices line

impedance will be 220Ω in series with 115nF in

parallel with 820Ω. See Table 3 and Figures 4 & 5.

Network Balance

Transhybrid loss is maximized when the line

termination impedance and SLIC network balance

are matched. The MH88625’s network balance

impedance set 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 N1 and

AGND, and NS at logic high, the devices network

balance impedance is 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 Figure 6.

12/16kHz Meter Pulse

The MH88625 provides control of an external signal

path to the driver. A 12/16kHz continuous signal can

be applied to the ESI pin. Control of the ESE input

allows the metering signal to be transmitted to the

line.

Unbalanced Detection

The Unbalanced Detect (UD) pin goes low when the

DC current through the two battery feed resistors is

unbalanced i.e., when the average DC current into

the Ring lead exceeds the current flow out of the Tip

lead (indicating that the Ring lead has been

grounded).

When the SLIC is interfaced to ground start

subscriber equipment during the idle state, the UD

output is monitored for indication of the subscribers

Ring Ground signal. The maximum loop current

supplied by the feed circuitry under this condition is

limited.

2-189

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