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參數(shù)資料
| 型號： | IDT821621 |
| 廠商： | Integrated Device Technology, Inc. |
| 英文描述： | LONG HAUL SLIC |
| 中文描述： | 長距離用戶接口 |
| 文件頁數(shù)： | 9/21頁 |
| 文件大?。?/td> | 322K |
| 代理商： | IDT821621 |
Functional Description
7
October 8, 2003
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.
LONG HAUL SLIC
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
!
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.
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 R
D,
which is connected between the RD and AGND pins. See
Figure 1
for
details.
Figure 1 Loop-Detect Threshold Setting
The loop current threshold I
ON
and I
OFF
are calculated by the
following equations:
R
D
The R-C network, formed by the capacitor C
D
and the resistor R
D,
determines the on-hook to off-hook time constant. The value of C
D
for a
typical on-hook to off-hook time constant of 0.5 ms is calculated by:
R
D
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 R
1
and R
2
.
The ring-trip detector monitors the loop status and reports it via the
DET
pin. When the loop goes off-hook, the bridging resistors R
B1
, R
B2
,
R
3
and R
4
, and the filter capacitors C
RT1
and C
RT2
cause the voltage on
DB to go positive with respect to DA and the
DET
pin goes low.
If R
LMAX
is the maximum line resistance to be detected as an off-
hook, the bridging resistors should be chosen as that:
R
R
3
R
4
R
LMAX
Where: R
FEED
= R
1
+ R
2
If the line resistance is less than R
LMAX
, it means that an off-hook
event occurs, otherwise, the loop is in on-hook state.
State
Control Pins
Two-Wire Status
DET
Output
C2
C1
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
Digital
Interface
A(TIP)
B(RING)
RD
DET
R
D
C
D
Two-wire
Interface
C1
C2
AGND
Off-hook
Detector
SLIC
I
ON
510
=
I
OFF
R
D
415
=
C
D
0.5ms
=
----------
B2
R
LMAX
---R
R
FEED
+
(
)
=
=
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