LE77D112BTC Zarlink, LE77D112BTC Datasheet - Page 4

• Manufacturer Part Number: LE77D112BTC
• Description: SLIC 1-CH 63dB 3.3V 44-Pin eTQFP Tray
• Manufacturer: Zarlink

Specifications of LE77D112BTC

• Package: 44eTQFP
• Number Of Channels Per Chip: 1
• Polarity Reversal: Yes
• Longitudinal Balanced: 63 dB
• Minimum Operating Supply Voltage: 3.135 V
• Typical Operating Supply Voltage: 3.3 V

Two-Wire Interface
The two-wire interface block provides DC current and sends/receives voice signals to a telephone connected via the A
B
device can also be programmed in Disconnect state to place the A and B pins at high impedance with the Switching Regulator
disabled.
DC Feed
DC feed control in the Le78D11/Le77D11 chip set is implemented in the Le77D11 VoSLIC device. The current limit threshold
(I
programmed up to 30 mA using the recommended R
Referring to
constant Tip-Ring voltage (V
the programmed current limit threshold (I
short circuit current is nominally 14.4 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 VoSLIC device 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
is buffered 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 filter is to separate the operation of the
DC feed from voice frequencies, preventing distortion and idle-channel noise.
Normal or Reverse Polarity is controlled by the Le78D11 VoSLAC device through the C3-1 state control pins. Some applications
require slew rate control of the transition between these feed states. The capacitor, C
time and create a quiet polarity change. In the Normal Active state, the NPRFILT
When Reverse Polarity is selected, C
In the Reverse Polarity state, the NPRFILT
current I
A 100-nF capacitor provides a nominal Normal Active to Reverse Polarity transition time of about 5 ms and a Reverse Polarity
to Normal Active transition time of 3 ms.
LTH
i
(Ring) pins. The A
) can be programmed via the MPI interface of the Le78D11 VoSLAC device. The current limit threshold (I
LOOP
NPR
V
(48 V)
AB
/500 becomes greater than I
, and the transition time is:
Figure
open
V
LPFi
0
AB
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 Le77D11 VoSLIC
I
LTH
NPRi
14.4 mA
LTH
LTH
is discharged by current I
i
/500, the difference is subtracted from CS1, and again filtered by C
pin is discharged near ground. When Normal Active is selected, C
I
). This region looks like a constant current source with 3.2 kΩ shunt resistor. The
SC
∆t
=
I
LOOP
V
-----------------------------------
i
Figure 3. DC Feed Curve
(TIP) and B
REF
Zarlink Semiconductor Inc.
∆t
i
DC
I
(TIP) and B
NPR
=
•
i
LTH
C
(TIP) and B
value.
(
-------------------------------------------------------- -
Figure
V
NPRi
.
CC
–
i
(RING) are swapped. When (I
V
4
LPFi
I
4. In the anti-sat region, current source CS1 creates a constant
REF
NPR
A
i
(RING).
(TIP) and V
i
. This filtered current is then steered by the Polarity Control,
NPR
) C
(RING) output amplifiers.
•
, and the transition time is:
NPRi
i
I
LTH
(TIP) is held constant, while B
I
B
SC
(RING). This voltage from the Level Shift block
i
=
pin is driven up to V
=
----------------------
R
NPRi
I
LTH
DC
V
DC
K
, may be used to increase the transition
+
DC
14.4mA
=
LOOP
V
---------- -
40
DC
-I
LTH
CC
)/500 = CS1], all of the
.
i
(RING) is changed
NPRi
LPFi
LTH
. This reduced
) can be
is charged by
i
(Tip) and