Le77D11
Notes:
1. V
DC
is programmable via the Le78D11 VoSLAC device. (V
DC
= 0.00 V to 1.20 V relative to V
REF
.)
2. V
REF
= 1.4 V nominal.
I
IMT
3. K
DC
= Le77D11 VoSLIC device DC current gain.
K
DC
= --------------
.
-
I
LOOP
4. R
DC
= external resistor 20 kΩ nominal.
5. V
AB
= V
Ai
– V
Bi
Tip-Ring differential voltage.
6. I
SC
= Loop short circuit current limit.
7. I
LTH
= Loop current limit threshold. I
LTH
should be programmed to 15 mA or less when in the Standby state.
8.
These are nominal values for DC feed curve. See the "Device Specifications" table for tolerance values.
Data Sheet
Figure 4.
VCC
DC Feed Block Diagram, Active and Standby Modes
CS1
I
LOOP
K
DC
VDC SLAC
R
DC
*
LPF
i
Current Mirrors
A
i
(TIP)
R
S
C
LPFi
*
I
A
RDC
i
I
LTH
K
DC
I
LOOP
Level Shift
Polarity Control
Sum/
Sense/
Fault
R
L
NPRFILT
i
C
NPRi
*
I
B
R
S
B
i
(RING)
IMT
i
I
LOOP
K
DC
F
i
Note:
* denotes external components
Ringing
Ringing is accomplished by placing the Le77D11 VoSLIC device into the Ringing state via the Le78D11 VoSLAC device's MPI
interface. Placing the Le77D11 VoSLIC device into the ringing state automatically enables signal generator A in the Le78D11
VoSLAC device which puts the ringing signal on the receive signal path (pin VIN). (For information on programming the Le78D11
VoSLAC device's signal generators, please refer to the
Le77D11 /Le78D11 Chip Set User’s Guide,
document ID# 080716). When
the Le77D11 VoSLIC device is in the ringing state, the gain from the input pin, VIN, to the output is K
R
, the ringing voltage gain.
The output waveform is a quasi-balanced waveform, as shown in
On the positive half cycle of the input waveform, when
(V
IN
– V
REF
) is positive, V
AB
is positive with V
A(TIP)
near –4 V and V
B(RING)
brought negative. When (V
IN
– V
REF
) is negative,
V
B(RING)
is held near –4 V and V
A(TIP)
is brought more negative. The waveform can be either sinusoidal or trapezoidal under the
control of the Le78D11 VoSLAC device.
To provide 90-V ringing capability, the application of a PNP bipolar switching transistor is used. For the reference schematic,
Zetex part FZT955 in a SOT-223 package is used. Its V
CEO
rating is 140 V. Due to the switching efficiency and overhead voltage,
one can achieve 90 Vpk sinusoidal ringing with a 5 REN load with V
SW
= 12 V. See
for external filters recommended for a 90-V peak ringing application.
5
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
