le9502 Zarlink Semiconductor, le9502 Datasheet - Page 4

• Manufacturer Part Number: le9502
• Description: Ringing Subscriber Line Interface Circuit
• Manufacturer: Zarlink Semiconductor

Two-Wire Interface
The two-wire interface block provides DC current and sends/receives voice signals to a telephone connected via the A
B
can also be programmed in Disconnect state to place the A
DC Feed
DC feed is controlled in the Le9502 RSLIC device. Only the current limit threshold (I
limit threshold can be set from 0 to 30 mA.
Referring to
constant Tip-Ring voltage (V
the programmed current limit threshold (I
short circuit current is nominally 17.0 mA greater than I
A block diagram of the DC feed control circuit is shown in
reference current, which is limited to sub-voice frequencies by C
depending on whether the SLIC mode is Standby, Normal Active, or Reverse Polarity. The steered current then takes one of two
paths to the Level Shift block, where it is used to set V
by the output amplifiers and appears at A
When I
current causes a reduced DC feed voltage. In Standby and Normal Active, A
to reduce the feed voltage. In Reverse Polarity, A
current from CS1 is subtracted, making the TIP-RING voltage = 0 V. This is the short circuit condition. At least 100 Ω loop and
fuse resistance are required to ensure stability of the A
The capacitor C
loop. This capacitor should nominally be 4.7 µF, setting a 1.4 Hz pole. The purpose of this capacitor is to stabilize the DC feed
and filter any AC components.
Note:
1.
2.
3.
4.
5.
i
(Ring) pins. The A
V
(48 V)
AB
R
V
K
I
I
SC
LTH
open
AB
DC
DC
LOOP
= Loop short circuit current limit.
= V
= Loop current limit threshold.
= external resistor from RDC to AGND
= Le9502 RSLIC device DC current gain, which is:
V
0
AB
Ai
/500 becomes greater than I
Figure
– V
LPFi
Bi
Tip-Ring differential voltage
3, the DC feed curve consists of two distinct regions. The first region is a flat anti-sat region that supplies a
, in conjunction with an internal 25 kΩ resistor (not shown), is used to create a low pass filter for the DC feed
i
(Tip) and B
AB
open). The second region is a constant current region that begins when the loop current reaches
i
(Ring) pins are also used to send the ringing signal to the telephone. The Le9502 RSLIC device
I
LTH
LTH
i
17.0 mA
LTH
(TIP) and B
/500, the difference is subtracted from CS1, and again filtered by C
). This region looks like a constant current source with 3.2 kΩ shunt resistor. The
Figure 3. DC Feed Curve
I
SC
i
(TIP) and B
Zarlink Semiconductor Inc.
i
A
I
K
LOOP
i
LTH
(RING).
(TIP) and V
(TIP) and B
DC
Figure
i
.
and B
=
-------- -
500
1
4
i
LPFi
I
(RING) are swapped. When (I
4. In the anti-sat region, current source CS1 creates a constant
SC
i
pins at high impedance with the Switching Regulator disabled.
I
LTH
i
B
. This filtered current is then steered by the Polarity Control,
=
(RING) output amplifiers.
(RING). This voltage from the Level Shift block is buffered
I
=
LTH
------------------------- -
R
DC
+
1.4 V
17.0mA
i
(TIP) is held constant, while B
K
DC
LTH
) can be set via the RDC pin. The current
LOOP
-I
LTH
)/500 = CS1, all of the
i
(RING) is changed
LPFi
. This reduced
i
(Tip) and