IDT821621 Просмотр технического описания (PDF) - Integrated Device Technology

Номер в каталоге

Компоненты Описание

производитель

IDT821621

LONG HAUL SLIC

Integrated Device Technology 

IDT821621

FUNCTIONAL DESCRIPTION

The IDT821621 implements the basic telephone line interface

functions. It provides many user programmable features including 2-wire

impedance matching, loop-detect threshold and ring-trip threshold

setting, constant current feeding, 4-wire to 2-wire gain setting, etc. The

following sections describe these functions in detail.

SLIC STATES CONTROL

The IDT821621 can be operated in Disconnect, Ringing, Active or

Standby state. A combination of the control pins C2 and C1 select one of

the possible four operating states. See Table 2 for details. The

IDT821621 provides an off-hook detector and a ring-trip detector on chip

to support the necessary signaling functions. The selection of the

detectors is based on the SLIC operating state. The output of the

detectors is reported through the DET pin. Once a hook switch event or

ring-trip event occurs, the DET pin goes low.

Table 2 — SLIC Operating States

Control Pins

State

Two-Wire Status

C2

C1

DET Output

0

0

0

Disconnect

Ring-trip Detector

1

0

1

Ringing

Ring-trip Detector

2

1

0

Active

Off-hook Detector

3

1

1

Standby

Off-hook Detector

! Disconnect

When the SLIC is in Disconnect state, both the TIP and RING

outputs are in high impedance condition. In this state, the off-hook

detector is inoperative and the power dissipation reduces to the lowest.

The Disconnect state is useful for out-of-service lines.

! Ringing

When the SLIC is in Ringing state, the ring relay driver (RINGOUT) is

activated and the TIP and RING outputs are in high impedance

condition. The ringing source is connected by an external ring relay to

the line. In Ringing state, the status of the ring-trip detector is reported

by the DET pin.

! Active

In Active state, the SLIC is fully functional. The standard battery

convention applies. All signal transmission and loop supervision

functions are active. The status of the off-hook detector is gated to the

DET pin.

! Standby

In Standby state, most of the internal circuitry is powered down,

resulting in low power dissipation. The off-hook detection function

operates normally, but signal transmission is not enabled. This state

allows for monitoring off-hook transitions while maintaining lowest

possible power consumption.

LONG HAUL SLIC

OFF-HOOK DETECTOR

The off-hook detector monitors the hook switch of the loop during

Active or Standby state. The output of the DET pin goes low when an

off-hook event is detected.

The loop-detect threshold is programmed by an external resistor RD,

which is connected between the RD and AGND pins. See Figure 1 for

details.

SLIC

Digital

Interface

A(TIP)

B(RING)

Two-wire

Interface

Off-hook

Detector

C1

C2

DET

AGND

RD

CD

RD

Figure 1 Loop-Detect Threshold Setting

The loop current threshold ION and IOFF are calculated by the

following equations:

ION

=

5----1---0--

RD

IOFF

=

4----1---5--

RD

The R-C network, formed by the capacitor CD and the resistor RD,

determines the on-hook to off-hook time constant. The value of CD for a

typical on-hook to off-hook time constant of 0.5 ms is calculated by:

CD

=

0----.-5----m------s-

RD

RING-TRIP DETECTOR

Figure 2 shows a general ringing circuit for the IDT821621. During

Ringing state, the on-chip ring relay driver (RINGOUT) is activated and

the ringing source is connected by the ring relay to the Tip and Ring

lines through the resistors R1 and R2.

The ring-trip detector monitors the loop status and reports it via the

DET pin. When the loop goes off-hook, the bridging resistors RB1, RB2,

R3 and R4, and the filter capacitors CRT1 and CRT2 cause the voltage on

DB to go positive with respect to DA and the DET pin goes low.

If RLMAX is the maximum line resistance to be detected as an off-

hook, the bridging resistors should be chosen as that:

R-----B----1- = -R----B----2- = -(--R-----L---M----A----X-----+-----R-----F---E----E---D----)-

R3 R4

RLMAX

Where: RFEED = R1 + R2

If the line resistance is less than RLMAX, it means that an off-hook

event occurs, otherwise, the loop is in on-hook state.

Functional Description

7

October 8, 2003

Share Link: