™
Le79555
Subscriber Line Interface Circuit
VE580 Series
APPLICATIONS
Ideal for high-density, low-power linecard applications
DESCRIPTION
The Le79555 device, part of Legerity’s VoiceEdge™ family
VE580 series of devices, was designed for high-density POTS
applications requiring a power saving, small footprint SLIC
device. The new SLIC device fulfills today's requirements for
POTS linecard markets requiring a balance of high-
performance cost-effective silicon components. The Le79555
device delivers economical linecard solutions by offering power
and space savings to linecard designers. The on-chip
switching regulator allows for power dissipation to be
minimized for the entire system. Another benefit is that the
device is offered in a reduced footprint package type, a 44-pin
TQFP. This small footprint saves designers board space, thus
increasing the density or number of lines on the board.
Legerity offers a range of compatible SLAC™ devices
providing a complete line circuit that can be optimized for
varying requirements. The SLIC device is designed to operate
with a range of SLAC devices from low cost, non-
programmable to more advanced, highly programmable
options viable for a range of applications.
FEATURES
Control states: Active, Reverse Polarity, Tip Open,
Ringing, Standby, and Open Circuit
Low Standby power
–40 to –58 V battery operation
On-hook transmission
Two-wire impedance set by single external impedance
Programmable constant-current feed
Low Off-Hook Active Overhead Voltage
Programmable loop-detect threshold
Ground-start detector
Programmable ring-trip detect threshold
No –5 V supply required
Three on-chip relay drivers and relay snubbers, one
ringing and two general purpose
Tip Open state for ground-start lines
On-chip switching regulator for Low power dissipation
Supports 30 mA for Active, Norma,l and Reverse
Polarity operation
RELATED LITERATURE
080125 SLIC Switcher Circuit Application Note
080725 Le79555 Switching Regulator Applications
080753 Le58QL02/021/031 QLSLAC™ Data Sheet
080754 Le58QL061/063 QLSLAC™ Data Sheet
ORDERING INFORMATION
Standard Packages
Device
Le79555-1VC
Le79555-1QC
Le79555-2VC
Le79555-2QC
Le79555-3VC
Le79555-3QC
Le79555-4VC
Le79555-4QC
Device
Le79555-1BVC
Le79555-1FQC
Le79555-2BVC
Le79555-2FQC
Le79555-3BVC
Le79555-3FQC
Le79555-4BVC
Le79555-4FQC
1.
Performance Grade/Package
52 dB Pol. Rev., 44-pin TQFP
52 dB Pol. Rev., 32-pin QFN
63 dB Pol. Rev., 44-pin TQFP
63 dB Pol. Rev., 32-pin QFN
52 dB No Pol. Rev., 44-pin TQFP
52 dB No Pol. Rev., 32-pin QFN
63 dB No Pol. Rev., 44-pin TQFP
63 dB No Pol. Rev., 32-pin QFN
Green Packages
1
Performance Grade/Package
52 dB Pol. Rev., 44-pin TQFP
52 dB Pol. Rev., 32-pin QFN
63 dB Pol. Rev., 44-pin TQFP
63 dB Pol. Rev., 32-pin QFN
52 dB No Pol. Rev., 44-pin TQFP
52 dB No Pol. Rev., 32-pin QFN
63 dB No Pol. Rev., 44-pin TQFP
63 dB No Pol. Rev., 32-pin QFN
Packing
Tray
Tray
2
Packing
2
Tray
Tray
BLOCK DIAGRAM
Ring Relay Driver
RINGOUT
A(TIP)
Relay Driver
RYOUT1
Tray
Relay Driver
RYOUT2
Tray
HPA
C1
C2
C3
Input Decoder
and Control
Two Wire
Interface
D1
D2
DET
Ground
Detector
HPB
Signal
Transmission
B(RING)
Off-Hook
Detector
VTX
RSN
Tray
Tray
VREG
DA
DB
Power Feed
Controller
RD
RDC
CAS
VDC
The green package meets RoHS Directive 2002/95/EC of the
European Council to minimize the environmental impact of
electrical equipment.
For delivery using a tape and reel packing system, add a "T" suffix
to the OPN (Ordering Part Number) when placing an order.
Ring-Trip
Detector
L
Switching Regulator
VBAT
BGND
2.
CHCLK
Document ID#
080686
Date:
Rev:
E
Version:
Distribution:
Public Document
AGND
QBAT
RSVD
CHS
VCC
Aug 29, 2005
1
TABLE OF CONTENTS
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Related Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Product Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Block Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Two-Wire Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Ground Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Signal Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Power Feed Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Switching Regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Input Decoder and Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Off-Hook Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Ring-Trip Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Ring Relay Driver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Relay Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Connection Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Pin Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Operating Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Transmission Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Longitudinal Capability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Idle Channel Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Insertion Loss and Balance Return Signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Line Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Power Supply Rejection Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Supply Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
RFI Rejection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Receive Summing Node (RSN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Logic Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Logic Output DET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Ring-Trip Detector Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Loop Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Relay Driver Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
DC Feed Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Test Circuit Scenarios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
APPLICATION CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Line card Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Physical Dimensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
44-Pin TQFP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
32-Pin QFN (8x8). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Revision C1 to C2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Revision C2 to D1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Revision D1 to E1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
2
Le79555 VE580 Series Data Sheet
PRODUCT DESCRIPTION
The Le79555 device is designed for short loop and long loop high-density POTS applications requiring a power saving, small
footprint SLIC. The Le79555 device boasts increased power savings over Legerity's other POTS solutions by using an internal
switching regulator for each channel to enhance system power management. The switching regulator eliminates the need for a
second voltage supply, commonly required for SLIC devices in POTS applications. Such elimination passes on board space and
cost savings to the designers. Thus, the smaller footprint and added features of the Le79555 device allows customers to amortize
the cost of common hardware across more channels and increase the line density per board. Additionally, the Le79555 device
gives line card designers a simple control interface that supports six control states: Active, Ringing, Standby, Disconnect, Reverse
Polarity, and Tip Open. The Le79555 device is a low cost, high performance device providing key features required for POTS
markets worldwide, including: low power dissipation and ground key detection, as well as all of the features offered currently by
Legerity's Transformer SLIC family, Le7920/22.
BLOCK DESCRIPTIONS
Two-Wire Interface
The two-wire interface provides DC current and sends voice signals to a telephone apparatus connected to the line card with a
two-wire line. The two-wire interface also receives the returning voice signals from the telephone.
Ground Detector
The ground detector block performs ground start and ground key detection, as well as automatically detects a ring-ground fault.
Therefore, when the longitudinal current is greater than the ground key detector threshold, IGK, in either Active, Standby, or Tip
Open, the DET will go low. Note that when the device is in Active or Standby, DET may be an indication of off-hook, ground fault,
or both.
Signal Transmission
The RSN input current controls the receive current sent to the two-wire interface. The AC line voltage is sensed by differential
amplifiers between the A and HPA leads, and between HPB and B leads. The outputs of these amplifiers are equal to the AC
metallic components of the line voltages. The transmission circuit also contains a longitudinal feedback circuit to shunt
longitudinal signals to a DC bias voltage. The longitudinal feedback does not affect metallic signals.
Power Feed Controller
The power feed controller has three sections: (1) the battery feed circuit, (2) the reverse polarity circuit, and (3) the bias circuit.
The battery feed circuit regulates the amount of DC current and voltage supplied to the telephone over a wide range of loop
resistance. The reverse polarity circuit provides the capability to reverse the loop current for pay telephone key pad disable and
other applications. The bias circuit provides a reference voltage, which is offset from the subscriber line voltage. The reference
voltage controls the switched mode regulator, which minimizes SLIC power consumption by providing the minimum supply
voltage needed by the line drivers for proper operation.
Switching Regulator
A switching regulator function is implemented on the chip with a few external components. The power feed controller generates
a reference voltage which is the minimum voltage required to feed the output line amplifiers. The efficiency of the switching
regulator (>80%) minimizes both the on-chip power dissipation and the system power dissipation. This is particularly important
for short loops operating at high currents which otherwise cause high power dissipation.
Input Decoder and Control
The input decoder and control block provides a means for a microprocessor or SLAC IC to control such system functions as line
activate, on-hook transmission, ringing, and reverse polarity. The input decoder and control block has TTL-compatible inputs,
which set the operating states of the SLIC. It also provides the supervision signal sent back to the controller.
Off-Hook Detector
The most important loop monitoring function is off-hook detection. The two-wire interface produces a current equal in magnitude
to the loop current divided by a constant, and sends it out on the RD pin. An external resistor and capacitor (RD and CD) connect
the RD pin to ground. The value of the voltage across resistor R
D
is proportional to the current leaving the RD pin times the value
of R
D
. The DET pin will show a logic Low when this voltage rises above a threshold.
Le79555 VE580 Series Data Sheet
3
Ring-Trip Detector
During the Ringing state, the DA pin is more positive than the DB pin, and the DET pin will show high to indicate the on hook.
When an off hook condition occurs, the DB pin becomes more positive than the DA pin, and the DET pin will go low to indicate
an off-hook.
Ring Relay Driver
The ring relay driver is active only in the Ringing state.
Relay Driver
A relay driver is activated by logic Low at either input pin, D1, or D2. D1 controls relay driver RYOUT1; D2 controls relay driver
RYOUT2.
4
Le79555 VE580 Series Data Sheet
CONNECTION DIAGRAMS
RINGOUT
B(RING)
VCC
VREG
BGND
A(TIP)
N/C
N/C
N/C
N/C
DB
44
RYOUT1
RYOUT2
L
VBAT
CHS
QBAT
CHCLK
N/C
D2
D1
C1
1
2
3
4
5
6
7
8
9
10
11
12
43
42
41
40
39
38
37
36
35 34
33
32
31
30
29
DA
N/C
RD
N/C
HPB
N/C
HPA
N/C
VTX
N/C
RSVD
44-Pin TQFP
28
27
26
25
24
23
13
14
15
16
17
18
19
20
21 22
C3
C2
N/C
N/C
CAS
VDC
N/C
RDC
RINGOUT
RYOUT1
B (RING)
VREG
VCC
BGND
A (TIP)
26
AGND/
DGND
RYOUT2
L
VBAT
CHS
QBAT
CHCLK
D2
D1
32
1
2
3
4
31
30
29
28
27
DB
25
24
23
22
21
RSN
DET
DA
N/C
RD
HPB
HPA
VTX
RSVD
RSN
32-Pin QFN
5
6
7
8
9
10
11
Exposed Pad
20
19
18
17
16
12
13
14
15
C1
C3
C2
Note:
1.
2.
3.
4.
Pin 1 is marked for orientation.
N/C = No Connect
RSVD = Reserved
There is VBAT potential on the exposed pad. Do not connect to GND pin.
Le79555 VE580 Series Data Sheet
RDC
ANGD/
DGND
VDC
DET
CAS
5
Microcontroller MCU
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