Agere ATTL7556AAU-TR Low-power slics with battery switch Datasheet

Data Sheet
January 2000
L7556, L7557 Low-Power SLICs
with Battery Switch
Features
■
Auxiliary input for second battery, and internal
switch to enable its use to save power
■
Low active power (typical 125 mW during on-hook
transmission)
■
Supports meter pulse injection
■
Spare op amp for meter pulse filtering
■
–16 V to –60 V power supply operation
■
Distortion-free on-hook transmission
■
Convenient operating states:
— Forward powerup
— Disconnect (high impedance)
— 2-wire wink (zero loop voltage)
■
Adjustable supervision functions:
— Off-hook detector with longitudinal rejection
— Ground key detector
— Ring trip detector
■
Independent, adjustable, dc and ac parameters:
— dc feed resistance
— Loop current limit
— Termination impedance
■
Thermal protection
Description
These electronic subscriber loop interface circuits
(SLICs) are optimized for low power consumption
while providing an extensive set of features.
The SLICs include an auxiliary battery input and a
built-in switch. In short-loop applications, they can be
used in high battery to present a high on-hook voltage, and then switched to low battery to reduce offhook power.
The SLICs also include a summing node for meter
pulse injection to 2.2 Vrms. A spare, uncommitted op
amp is included for meter pulse filtering.
The switched battery is applied to the power amplifiers of the device. There are two versions. The L7556
has the battery switch completely under processor
control. The L7557 can automatically switch to lower
battery when appropriate and includes hysteresis to
avoid frequent switching. To make the switch silent,
an external capacitor can be added to slow the transition.
The L7556 is suited for applications serving only
short loops, where a high on-hook voltage is required
for compatibility with preexisting standards.
The L7557 is suited for applications where a full loop
range is needed, but low short-loop power is desired.
It is a much lower-cost solution than a switching regulator, and also occupies much less PCB area, needing only a battery filter capacitor and a diode for
implementation.
The device is available in a 32-pin PLCC package. It
is built by using a 90 V complementary bipolar integrated circuit (CBIC) process.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Table of Contents
Contents
Page
Features ..................................................................... 1
Description .................................................................. 1
Pin Information ............................................................ 4
Functional Description ................................................. 6
Absolute Maximum Ratings ........................................ 6
Recommended Operating Conditions ......................... 7
Electrical Characteristics ............................................. 7
Ring Trip Requirements ......................................... 11
Test Configurations .................................................. 12
Applications .............................................................. 14
Design Considerations ........................................... 16
Characteristic Curves............................................. 17
dc Applications ....................................................... 20
Battery Feed......................................................... 20
Switching the Battery............................................ 20
Overhead Voltage ............................................... 21
Adjusting Overhead Voltage ................................ 21
Adjusting dc Feed Resistance.............................. 22
Loop Range.......................................................... 22
Off-Hook Detection .............................................. 22
Ring Trip Detection.............................................. 23
Ring Ground Detection........................................ 23
ac Design ............................................................... 24
First-Generation Codecs ..................................... 24
Second-Generation Codecs ................................ 24
Third-Generation Codecs .................................... 24
Selection Criteria ................................................. 24
PCB Layout Information ............................................ 26
Outline Diagram......................................................... 27
32-Pin PLCC ........................................................... 27
Ordering Information.................................................. 28
Tables
Page
Table 1. Pin Descriptions ............................................ 4
Table 2. Input State Coding ........................................ 6
Table 3. Supervision Coding ....................................... 6
Table 4. Power Supply ................................................ 7
Table 5. 2-Wire Port .................................................... 8
Table 6. Analog Pin Characteristics ............................ 9
Table 7. Uncommitted Op Amp Characteristics .......... 9
Table 8. ac Feed Characteristics .............................. 10
Table 9. Logic Inputs and Outputs ............................ 11
Table 10. Parts List for Loop Start and Ground
Start Applications ...................................... 15
Table 11. 600 Ω Design Parameters ......................... 16
2
Figures
Page
Figure 1. Functional Diagram ..................................... 3
Figure 2. Pin Diagram (PLCC Chip) ........................... 4
Figure 3. Ring Trip Circuits ....................................... 11
Figure 4. Basic Test Circuit .......................................12
Figure 5. Longitudinal Balance .................................12
Figure 6. Longitudinal PSRR ....................................13
Figure 7. RFI Rejection .............................................13
Figure 8. Longitudinal Impedance ............................13
Figure 9. Metallic PSRR ...........................................13
Figure 10. ac Gains ..................................................13
Figure 11. Basic Loop Start Application Circuit
Using T7504 Type Codec ........................14
Figure 12. Ring Ground Detection Circuit .................14
Figure 13. Receive Gain and Hybrid Balance vs.
Frequency ...............................................17
Figure 14. Transmit Gain and Return Loss vs.
Frequency ...............................................17
Figure 15. Typical VCC Power Supply Rejection .......17
Figure 16. Typical VBAT Power Supply
Rejection .................................................17
Figure 17. Loop Closure Program Resistor
Selection ..................................................18
Figure 18. Ring Ground Detection Programming .....18
Figure 19. Loop Current vs. Loop Voltage ................18
Figure 20. Loop Current vs. Loop Resistance ..........18
Figure 21. Typical SLIC Power Dissipation vs.
Loop Resistance ......................................19
Figure 22. Power Derating ........................................19
Figure 23. Longitudinal Balance Resistor Mismatch
Requirements ..........................................19
Figure 24. Longitudinal Balance vs. Protection
Resistor Mismatch ...................................19
Figure 25. Loop Current vs. Loop Voltage ................20
Figure 26. SLIC 2-Wire Output Stage .......................21
Figure 27. Equivalent Circuit for Adjusting the Overhead Voltage ...........................................21
Figure 28. Equivalent Circuit for Adjusting the dc
Feed Resistance ......................................22
Figure 29. Adjusting Both Overhead Voltage and dc
Feed Resistance .....................................22
Figure 30. Off-Hook Detection Circuit
Applications .............................................22
Figure 31. Ring Trip Equivalent Circuit and
Equivalent Application .............................23
Figure 32. ac Equivalent Circuit Not Including Spare
Op Amp ...................................................25
Figure 33. ac Equivalent Circuit Including Spare
Op Amp ...................................................25
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
BATTERY
SWITCH
AGND
VCC
BGND
IPROG
BS2
BS1
VBAT1
VBAT2
LBAT
BS
Description (continued)
POWER CONDITIONING
& REFERENCE
VREG
CF1
CF2
DCOUT
+
VITR
1 V/8 mA
–
SN
PT
A=4
SPARE
OP AMP
–
XMT
+
PR
–
RCVN
+
RCVP
A = –4
B0
DCR
BATTERY FEED
STATE CONTROL
dc RESISTANCE
ADJUST
B1
LCTH
LOOP CLOSURE DETECTOR
+
NLC
–
+
RTSP
RTSN
ICM
RING TRIP DETECTOR
NRDET
–
RING GROUND
DETECTOR
RGDET
12-2551.a (F)
Figure 1. Functional Diagram
Lucent Technologies Inc.
3
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
NC
LBAT
BS
IPROG
VBAT2
BS1
BS2
NC
Pin Information
4
3
2
1
32
31
30
VCC
5
29
SN
RCVP
6
28
XMT
RCVN
7
27
B1
LCTH
8
26
NLC
DCOUT
9
25
NRDET
32-PIN PLCC
RTSN
CF2
12
22
PT
CF1
13
21
BGND
14
15
16
17
18
19
20
DCR
23
AGND
11
AGND
PR
B0
RTSP
RGDET
24
ICM
10
VITR
VBAT1
12-2548.q (F)
Figure 2. Pin Diagram (PLCC Chip)
Table 1. Pin Descriptions
Pin
1
2
3
4
4
5
6
7
8
9
10
4
Symbol Type
Description
VBAT2
— Auxiliary Battery Supply. Negative high-voltage battery, lower in magnitude than
VBAT1, used to reduce power dissipation on short loops.
IPROG
I
Current-Limit Program Input. A resistor to DCOUT sets the dc current limit of the
device.
BS
I
Battery Switch. See Table 2 for description.
NC
— No Connection (L7556 Only). Do not use as a tie point.
LBAT
O
Lower Battery in Use (L7557 Only). When high, this open-collector output indicates
the device has switched to VBAT2. To use, connect a 100 kΩ resistor to VCC.
VCC
— +5 V Power Supply.
RCVP
I
Receive ac Signal Input (Noninverting). This high-impedance input controls the ac
differential voltage on tip and ring.
RCVN
I
Receive ac Signal Input (Inverting). This high-impedance input controls the ac differential voltage on tip and ring.
LCTH
I
Loop Closure Threshold Input. Connect a resistor to DCOUT to set off-hook threshold.
DCOUT
O
dc Output Voltage. This output is a voltage that is directly proportional to the absolute
value of the differential tip/ring current.
VBAT1
— Battery Supply. Negative high-voltage power supply, higher in magnitude than VBAT2.
Lucent Technologies Inc.
Data Sheet
January 2000
L7556, L7557 Low-Power SLICs
with Battery Switch
Pin Information (continued)
Table 1. Pin Descriptions (continued)
Pin
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Symbol Type
Description
PR
I/O Protected Ring. The output of the ring driver amplifier and input to loop sensing circuitry. Connect to loop through overvoltage protection.
CF2
— Filter Capacitor 2. Connect a 0.1 µF capacitor from this pin to AGND.
CF1
— Filter Capacitor 1. Connect a 0.47 µF capacitor from this pin to pin CF2.
VITR
O
Transmit ac Output Voltage. This output is a voltage that is directly proportional to the
differential tip/ring current.
ICM
I
Common-Mode Current Sense. To program ring ground sense threshold, connect a
resistor to VCC and connect a capacitor to AGND to filter 50/60 Hz. If unused, the pin
can be left unconnected.
RGDET
O
Ring Ground Detect. When high, this open-collector output indicates the presence of
a ring ground. To use, connect a 100 kΩ resistor to VCC.
B0
I
State Control Input. B0 and B1 determine the state of the SLIC. See Table 2.
AGND
— Analog Signal Ground.
AGND
— Analog Signal Ground.
DCR
I
dc Resistance for Low Loop Currents. Leave open for dc feed resistance of 115 Ω,
or short to DCOUT for 615 Ω. Intermediate values can be set by a simple resistor
divider from DCOUT to ground with the tap at DCR.
BGND
— Battery Ground. Ground return for the battery supply.
PT
I/O Protected Tip. The output of the tip driver amplifier and input to loop sensing circuitry.
Connect to loop through overvoltage protection.
RTSN
I
Ring Trip Sense Negative. Connect this pin to the ringing generator signal through a
high-value resistor.
RTSP
I
Ring Trip Sense Positive. Connect this pin to the ring relay and the ringer series resistor through a high-value resistor.
NRDET
O
Ring Trip Detector Output. When low, this logic output indicates that ringing is tripped.
NLC
O
Loop Detector Output. When low, this logic output indicates an off-hook condition.
B1
I/O State Control Input. B0 and B1 determine the state of the SLIC. See Table 2. Pin B1
has a 40 kΩ pull-up. It goes low in the event of thermal shutdown.
XMT
O
Transmit ac Output Voltage. The output of the uncommitted operational amplifier.
SN
I
Summing Node. The inverting input of the uncommitted operational amplifier. A resistor or network to XMT sets the gain.
NC
— No Connection. Do not use as a tie point.
BS2
— Battery Switch Slowdown. A 0.1 µF capacitor from BS1 to BS2 will ramp the battery
switch transition for applications requiring quiet transition. If not needed, the pin can be
left open.
BS1
— Battery Switch Slowdown. A 0.1 µF capacitor from BS1 to BS2 will ramp the battery
switch transition for applications requiring quiet transition. If not needed, the pin can be
left open.
Lucent Technologies Inc.
5
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Functional Description
Table 2. Input State Coding
B0 B1
1
1
BS
1
1
1
0
1
0
1
0
0
1
State/Definition
Powerup, Forward Battery. Normal talk and battery feed state. Pin PT is positive with respect
to PR. On-hook transmission is enabled. VBAT1 is applied to entire circuit.
Powerup, Forward Battery. Normal talk and battery feed state. Pin PT is positive with respect
to PR. On-hook transmission is enabled.
For the L7556 only, VBAT2 is applied to tip/ring drive amplifiers.
For the L7557 only, the device compares the magnitude of VBAT2 to the voltage necessary to
maintain proper loop current. Then the device automatically applies VBAT2 to tip/ring drive amplifiers when possible, not affecting the desired dc template.
2-Wire Wink. Pins PT and PR are put at the same potential (near ground). VBAT1 is applied to
entire circuit.
Disconnect. The tip and ring amplifiers are turned off, and the SLIC goes to a high-impedance
state (>100 kΩ).VBAT1 is applied to entire circuit.
Table 3. Supervision Coding
Pin NLC
0 = off-hook
1 = on-hook
Pin NRDET
0 = ring trip
1 = no ring trip
Pin RGDET
1 = ring ground
0 = no ring ground
Absolute Maximum Ratings (TA = 25 °C)
Stresses in excess of the Absolute Maximum Ratings can cause permanent damage to the device. These are
absolute stress ratings only. Functional operation of the device is not implied at these or any other conditions in
excess of those given in the operational sections of the data sheet. Exposure to Absolute Maximum Ratings for
extended periods can adversely affect device reliability.
Parameter
5 V Power Supply
Battery (Talking) Supply
Auxiliary Battery Supply
Logic Input Voltage
Analog Input Voltage
Maximum Junction Temperature
Storage Temperature Range
Relative Humidity Range
Ground Potential Difference (BGND to AGND)
PT or PR Fault Voltage (dc)
PT or PR Fault Voltage (10 x 1000 µs)
Current into Ring Trip Inputs
Note:
6
Symbol
VCC
VBAT1
VBAT2
—
—
TJ
Tstg
RH
—
VPT, VPR
VPT, VPR
IRTSP, IRTSN
Value
7.0
–63
–63
–0.5 to +7.0
–7.0 to +7.0
165
–40 to +125
5 to 95
±3
(VBAT1 – 5) to +3
(VBAT1 – 15) to +15
±240
Unit
V
V
V
V
V
°C
°C
%
V
V
V
µA
The IC can be damaged unless all ground connections are applied before, and removed after, all other connections. Furthermore, when
powering the device, the user must guarantee that no external potential creates a voltage on any pin of the device that exceeds the
device ratings. Some of the known examples of conditions that cause such potentials during powerup are the following:
1. An inductor connected to tip and ring can force an overvoltage on VBAT through the protection devices if the VBAT connections chatter.
2. Inductance in the VBAT leads could resonate with the VBAT filter capacitors to cause a destructive overvoltage.
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Recommended Operating Conditions
Parameter
Ambient Temperature
VCC Supply Voltage
VBAT1 Supply Voltage
VBAT2 Supply Voltage
Loop Closure Threshold-detection Programming Range
dc Loop Current-limit Programming Range
On- and Off-hook 2-wire Signal Level
ac Termination Impedance Programming Range
Min
–40
4.75
–24
–16
—
5
—
150
Typ
—
5.0
–48
–28
10
22
1
600
Max
85
5.25
–60
VBAT1
ILIM
45
2.2
1300
Unit
°C
V
V
V
mA
mA
Vrms
Ω
Electrical Characteristics
Minimum and maximum values are testing requirements. Typical values are characteristic of the device and are
the result of engineering evaluations. Typical values are for information purposes only and are not part of the testing requirements. Minimum and maximum values apply across the entire temperature range (–40 °C to +85 °C)
and the entire battery range unless otherwise specified. Typical is defined as 25 °C, VCC = 5.0 V, VBAT1 = –48 V,
VBAT2 = –48 V, and ILIM= 40 mA. Positive currents flow into the device. Test circuit is Figure 4 unless noted.
Table 4. Power Supply
Parameter
Power Supply—Powerup, No Loop Current:
ICC
IBAT (VBAT = –48 V)
Power Dissipation (VBAT = –48 V)
Power Supply Rejection 500 Hz to 3 kHz (See Figures 5, 6, 15, and 16.)1:
VCC
VBAT
Thermal Protection Shutdown (Tjc)
Thermal Resistance, Junction to Ambient (θJA)
Min
Typ
Max
Unit
—
—
—
2.8
–2.3
125
—
—
155
mA
mA
mW
35
45
—
—
—
—
dB
dB
—
—
175
60
—
—
°C
°C/W
1. This parameter is not tested in production. It is guaranteed by design and device characterization.
Lucent Technologies Inc.
7
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Electrical Characteristics (continued)
Table 5. 2-Wire Port
Min
Typ
Max
Unit
Tip or Ring Drive Current:
= dc + Longitudinal + Signal Currents
Parameter
65
—
—
mA
Signal Current
15
—
—
mArms
8.5
15
—
mArms
—
5
—
ILIM
—
—
—
45
±12
mA
mA
%
Longitudinal Current Capability per
Wire1
dc Loop Current Limit2:
RLOOP = 100 Ω
Programmability Range
Accuracy (20 mA < ILIM < 40 mA)
Powerup Open Loop Voltage Levels (includes external diode):
|VBAT + 8.4| |VBAT + 7.9| |VBAT + 7.4|
Differential Voltage
V
Disconnect State:
PT Resistance (VBAT < VPT < 0 V)
PR Resistance (VBAT < VPR < 0 V)
100
100
143
133
—
—
kΩ
kΩ
Ground Start State:
PT Resistance
100
143
—
kΩ
dc Feed Resistance (for ILOOP below regulation level)
95
115
135
Ω
1885
685
—
—
—
—
Ω
Ω
Longitudinal to Metallic Balance—IEEE 3 Std. 455 (See
Figure 6.)4:
50 Hz to 1 kHz
1 kHz to 3 kHz
64
60
75
70
—
—
dB
dB
Metallic to Longitudinal Balance:
200 Hz to 4 kHz
46
—
—
dB
—
–55
–45
dBV
Loop Resistance Range (–3.17 dBm overload into 600 Ω; not
including protection):
ILOOP = 20 mA at VBAT2 = –48 V
ILOOP = 20 mA at VBAT2 = –24 V
7.)5:
RFI Rejection (See Figure
0.5 Vrms, 50 Ω Source, 30% AM Mod 1 kHz
500 kHz to 100 MHz
1. The longitudinal current is independent of dc loop current.
2. Current-limit ILIM is programmed by a resistor, RPROG, from pin IPROG to DCOUT. ILIM is specified at the loop resistance where current limiting
begins (see Figure 19). Select RPROG (kΩ) =1.67 x ILIM (mA).
3. IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
4. Longitudinal balance of circuit card will depend on loop series resistance matching (see Figure 23 and Figure 24).
5. This parameter is not tested in production. It is guaranteed by design and device characterization.
8
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Electrical Characteristics (continued)
Table 6. Analog Pin Characteristics
Parameter
Min
Typ
Max
Unit
–123
–125
–127
V/A
Loop Closure Detector Threshold1:
Programming Accuracy
—
—
±20
%
Ring Ground Detector Threshold2:
RICM = 154 kΩ
Programming Accuracy
3
—
6
—
10
±25
kΩ
%
Ring Trip Comparator:
Input Offset Voltage
—
—
±10
mV
RCVN, RCVP:
Input Bias Current
—
–0.2
–1
µA
Min
Typ
Max
Unit
Input Offset Voltage
Input Offset Current
Input Bias Current
Differential Input Resistance
—
—
—
—
±5
±10
200
1.5
—
—
—
—
mV
nA
nA
MΩ
Output Voltage Swing (RL = 10 kΩ)
Output Resistance (AVCL = 1)
—
—
±3.5
2.0
—
—
Vpk
Ω
Small Signal GBW
—
700
—
kHz
Differential PT/PR Current Sense (DCOUT):
Gain (PT/PR to DCOUT)
1. Loop closure threshold is programmed by resistor RLCTH from pin LCTH to pin DCOUT.
2. Ring ground threshold is programmed by resistor RICM2 from pin ICM to VCC.
Table 7. Uncommitted Op Amp Characteristics
Parameter
Lucent Technologies Inc.
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L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Electrical Characteristics (continued)
Table 8. ac Feed Characteristics
Parameter
Min
Typ
Max
Unit
150
—
1300
Ω
Longitudinal Impedance (See Figure 8.)
—
40
46
Ω
Total Harmonic Distortion—200 Hz to 4 kHz2:
Off-hook
On-hook
—
—
—
—
0.3
1.0
%
%
Transmit Gain, f = 1 kHz (PT/PR to VITR)
Transmit Accuracy in dB
–122
–0.18
–125
0
–128
0.18
V/A
dB
Receive + Gain, f = 1 kHz (RCVP to PT/PR)
Receive – Gain, f = 1 kHz (RCVN to PT/PR)
Receive Accuracy in dB
7.84
–7.84
–0.18
8.00
–8.00
0
8.16
–8.16
0.18
—
—
dB
Gain vs. Frequency (transmit and receive) (600 Ω termination; reference 1 kHz2):
–1.00
200 Hz to 300 Hz
–0.3
300 Hz to 3.4 kHz
–3.0
3.4 kHz to 16 kHz
—
16 kHz to 266 kHz
0.0
0.0
–0.1
—
0.05
0.05
0.3
2.0
dB
dB
dB
dB
–0.05
0
0.05
dB
Return
200 Hz to 500 Hz
500 Hz to 3400 Hz
20
26
24
29
—
—
dB
dB
2-wire Idle-channel Noise (600 Ω termination):
Psophometric
C-message
3 kHz Flat
—
—
—
–87
2
10
–77
12
20
dBmp
dBrnC
dBrn
Transmit Idle-channel Noise:
Psophometric
C-message
3 kHz flat
—
—
—
–82
7
15
–77
12
20
dBmp
dBrnC
dBrn
Transhybrid Loss3:
200 Hz to 500 Hz
500 Hz to 3400 Hz
21
26
24
29
—
—
dB
dB
ac Termination
Impedance1:
2
Gain vs. Level (transmit and receive)(reference 0 dBV2):
–50 dB to +3 dB
Loss3:
1. Set by external components. Any complex impedance R1 + R2 || C between 150 Ω and 1300 Ω can be synthesized.
2. This parameter is not tested in production. It is guaranteed by design and device characterization.
3. Return loss and transhybrid loss are functions of device gain accuracies and the external hybrid circuit. Guaranteed performance assumes
1% tolerance external components.
10
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Electrical Characteristics (continued)
Table 9. Logic Inputs and Outputs
All outputs except RGDET and LBAT are open collectors with internal, 30 kΩ pull-up resistor. RGDET and LBAT are
open collectors without internal pull-up. Input pin B1 has a 40 kΩ pull-up; it goes low in the event of thermal shutdown.
Parameter
Symbol
Min
Typ
Max
Unit
Input Voltages:
Low Level (permissible range)
High Level (permissible range)
VIL
VIH
–0.5
2.0
0.4
2.4
0.7
VCC
V
V
Input Currents:
Low Level (VCC = 5.25 V, VI = 0.4 V)
High Level (VCC = 5.25 V, VI = 2.4 V)
IIL
IIH
–75
–40
–115
–60
–200
–100
µA
µA
VOL
VOH
0
2.4
0.2
—
0.4
VCC
V
V
Output Voltages (open collector with internal pull-up resistor):
Low Level (VCC = 4.75 V, IOL = 360 µA)
High Level (VCC = 4.75 V, IOH = –20 µA)
Ring Trip Requirements
■
■
■
200 Ω
Ringing signal:
— Voltage, minimum 35 Vrms, maximum 100 Vrms.
— Frequency, 17 Hz to 23 Hz.
— Crest factor, 1.4 to 2.
TIP
Ringing trip:
— ≤100 ms (typical), ≤250 ms (VBAT = –33 V, loop
length = 530 Ω).
TIP
RING
SWITCH CLOSES <12 ms
6 µF
RING
10 kΩ
Pretrip:
— The circuits in Figure 3 will not cause ringing trip.
2 µF
100 Ω
TIP
RING
12-2572g (F)
Figure 3. Ring Trip Circuits
Lucent Technologies Inc.
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L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Test Configurations
VBAT1
0.1 µF
VCC
VBAT2
0.1 µF
0.1 µF
VBAT1 VBAT2 BGND VCC AGND
BS1
LBAT
100 Ω
TIP
BS2
PT
0.47 µF
VITR
RLOOP
100 Ω
100 Ω
RING
20 kΩ
L7556
L7557
SLIC
SN
95.3 kΩ
XMT
PR
XMT
DCOUT
68.1 kΩ
RCVN
IPROG
0.1 µF
11 kΩ
RCVP
24.9 kΩ
LCTH
B0
B1
BS
NLC
RTSP
NRDET
RGDET
CF1
2 MΩ
402 Ω
RTSN
274 kΩ
76.8 kΩ
11 kΩ
0.1 µF
2 MΩ
ICM
RCV
CF2
0.1 µF
VBAT
12-2564.a (F)
Figure 4. Basic Test Circuit
100 µF
TIP
VS
368 Ω
+
VM
368 Ω
BASIC
TEST CIRCUIT
–
RING
100 µF
LONGITUDINAL BALANCE = 20 log
VS
VM
12-2584.c (F)
Figure 5. Longitudinal Balance
12
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Test Configurations (continued)
ILONG
TIP
+
VPT
–
V BAT OR VCC
100 Ω
4.7 µF
DISCONNECT
BYPASS CAPACITOR
ILONG
VS
–
VPR
+
V BAT OR
V CC
BASIC
TEST CIRCUIT
RING
67.5 Ω
TIP
10 µF
ZLONG =
BASIC
TEST CIRCUIT
12-2585.a (F)
67.5 Ω
+
VM
–
Figure 8. Longitudinal Impedance
RING
56.3 Ω
∆VPR
∆ VPT
OR
∆ ILONG
∆ ILONG
10 µF
PSRR = 20log
V BAT OR VCC
VS
VM
100 Ω
DISCONNECT
BYPASS CAPACITOR
4.7 µF
12-2583.b (F)
VS
Figure 6. Longitudinal PSRR
VBAT OR
VCC
TIP
0.01 µF
82.5 Ω
+
TIP
600 Ω
50 Ω
VS
0.01 µF
900 Ω
1
6, 7
LB1201
2.15 µF
4
2
V BAT
VT/R
–
BASIC TEST
CIRCUIT
BASIC
TEST CIRCUIT
RING
RING
PSRR = 20log
82.5 Ω
VS
VT/R
HP * 4935A
TIMS
12-2582.b (F)
Figure 9. Metallic PSRR
VS = 0.5 Vrms 30% AM 1 kHz MODULATION,
f = 500 kHz—1 MHz
DEVICE IN POWERUP MODE, 600 Ω TERMINATION
5-6756.b (F)
* HP is a registered trademark of Hewlett-Packard Company.
XMT
TIP
Figure 7. RFI Rejection
+
600 Ω
VT/R
–
BASIC
TEST CIRCUIT
RCV
RING
VS
VXMT
GXMT = VT/R
GRCV =
VT/R
VRCV
12-2587.e (F)
Figure 10. ac Gains
Lucent Technologies Inc.
13
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications
VBAT1
VCC
CBAT1
0.1 µF
66.8 kΩ
2
9
RLCTH
VCC
CROWBAR
PROTECTOR
TIP
RPT
50 Ω
24.9 kΩ
CBAT2
0.1 µF
DBAT
RPROG
8
5
10
1
21
CCC
0.1 µF
4
5
BGND LBAT VCC
IPROG VBAT1 VBAT2
19
DCOUT
VITR
LCTH
VCC
CB2
0.47 µF
RCVP
22
PR
CROWBAR
PROTECTOR
RTS1
402 Ω
CRTS2
0.27 µF
CRTS1
0.022 µF
RTS2
274 kΩ
RTSN
2.0 MΩ
23
VRING
VBAT
RHB1
90.9 kΩ
RRCV
84.5 kΩ
RGP
57.6 kΩ
RCVN
RING
24
VFXIN
–
PCM
HIGHWAY
VFXIP PWROP
B1
B0
BS
RTSP
NLC
NRDET
RTSN CF2
12
CF1
13
AGND AGND
18
19
CGP
330 pF
7
DX
+
6
L7556/L7557
SLIC
11
GSX
RT2
18.7 kΩ
PT
L7581
RELAY
RTSP
2.0 MΩ
CB1
0.47 µF
14
RT1
54.9 kΩ
CCC
0.1 µF
RPR
50 Ω
RX
90.9 kΩ
AGND
DR
FSX
FSEP
MCLK
SYNC
AND
CLOCK
ASEL
CONTROL
INPUT
1/4 T7504
CODEC
27 CONTROL
17
INPUTS
4
26 SUPERVISION
25
OUTPUTS
BGND
21
CF1
0.47 µF
CF2
0.1 µF
12-2573.Y(F)
Notes:
Tx = 0 dB.
Rx = 0 dB.
Termination = 600 Ω.
Transhybrid = 600 Ω.
Figure 11. Basic Loop Start Application Circuit Using T7504 Type Codec
VCC
GROUND START
APPLICATION CIRCUIT
RGDET
100 kΩ
RGDET
RICM2
154 kΩ
RGDET
ICM
CICM
0.47 µF
12-3547(F)
Figure 12. Ring Ground Detection Circuit
14
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
Table 10. Parts List for Loop Start and Ground Start Applications
Name
Integrated Circuits
SLIC
Protector
Ringing Relay
Codec
Overvoltage Protection
RPT
RPR
Power Supply
CBAT1
CBAT2
CCC
CF1
CF2
DBAT
dc Profile
RPROG
ac Characteristics
CB1
CB2
RT1
RRCV
RGP
CGP
RT2
RX
RHB1
Value
Function
L7556/7557
Crowbar protector*
L7581
T7504
Subscriber loop interface circuit (SLIC).
Secondary protection.
Switches ringing signals.
First-generation codec.
50 Ω, PTC or Fusible
50 Ω, PTC or Fusible
Protection resistor.
Protection resistor.
0.1 µF, 20%, 100 V
0.1 µF, 20%, 100 V
0.1 µF, 20%, 10 V
0.47 µF, 20%, 100 V
0.1 µF, 20%, 100 V
100 V, 150 mA
VBAT1 filter capacitor.
VBAT2 filter capacitor.
VCC filter.
With CF2, improves idle channel noise.
With CF1, improves idle channel noise.
Transient protection diode.
66.8 kΩ, 1%, 1/16 W
Sets dc loop current limit.
0.47 µF, 20%, 10 V
0.47 µF, 20%, 10 V
54.9 kΩ, 1%, 1/16 W
84.5 kΩ, 1%, 1/16 W
57.6 kΩ, 1%, 1/16 W
ac/dc separation capacitor.
ac/dc separation capacitor.
With RGP and RRCV, sets ac termination impedance.
With RGP and RT1, sets receive gain.
With RT1 and RRCV, sets ac termination impedance
and receive gain.
Loop stability.
With RX, sets transmit gain in codec.
With RT2, sets transmit gain in codec.
Sets hybrid balance.
330 pF, 10 V, 20%
18.7 kΩ, 1%, 1/16 W
90.9 kΩ, 1%, 1/16 W
90.9 kΩ, 1%, 1/16 W
* Contact your Lucent Technologies account representative for protector recommendations. Choice of this (and all) component(s) should be
evaluated and confirmed by the customer prior to use in any field or laboratory system. Lucent does not recommend use of this part in the
field without performance verification by the customer. This device is suggested by Lucent for customer evaluation. The decision to use a
component should be based solely on customer evaluation.
Lucent Technologies Inc.
15
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
Table 10. Parts List for Loop Start and Ground Start Applications (continued)
Name
Supervision
RLCTH
RTS1
RTS2
CRTS1
CRTS2
RTSN
RTSP
Ground Start
CICM
RGDET
RICM2
Value
24.9 kΩ, 1%, 1/16 W
402 Ω, 5%, 2 W
274 kΩ, 1%, 1/16 W
Function
0.022 µF, 20%, 5 V
0.27 µF, 20%, 100 V
2 MΩ, 1%, 1/16 W
2 MΩ, 1%, 1/16 W
Sets loop closure (off-hook) threshold.
Ringing source series resistor.
With CRTS2, forms first pole of a double pole,
2 Hz ring trip sense filter.
With RTSN, RTSP, forms second 2 Hz filter pole.
With RTS2, forms first 2 Hz filter pole.
With CRTS1, RTSP, forms second 2 Hz filter pole.
With CRTS1, RTSN, forms second 2 Hz filter pole.
0.47 µF, 20%, 10 V
100 kΩ, 20%, 1/16 W
82.5 kΩ, 1%, 1/16 W
Provides 60 Hz filtering for ring ground detection.
Digital output pull-up resistor.
Sets ring ground detection threshold.
Design Considerations
Table 11 shows the design parameters of the application circuit shown in Figure 11. Components that are adjusted
to program these values are also shown.
Table 11. 600 Ω Design Parameters
Design Parameter
Parameter Value
Components Adjusted
Loop Closure Threshold
10 mA
RLCTH
dc Loop Current Limit
40 mA
RPROG
dc Feed Resistance
180 Ω
RPT, RPR
3.14 dBm
—
ac Termination Impedance
600 Ω
RT1, RGP, RRCV
Hybrid Balance Line Impedance
600 Ω
RHB1
Transmit Gain
0 dB
RT2, RX
Receive Gain
0 dB
RRCV, RGP, RT1
2-wire Signal Overload Level
16
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
0
Characteristic Curves
–10
PSRR (dB)
–20
0
–10
RECEIVE GAIN
CURRENT
LIMIT
–30
SPEC.
–40
BELOW
–50 CURRENT
LIMIT
–60
–20
(dB)
–70
–80
10
–30
1000
104
105
106
FREQUENCY (Hz)
HYBRID BALANCE
–40
–50
100
100
12-2830.a (F)
1000
104
105
Figure 15. Typical VCC Power Supply Rejection
FREQUENCY (Hz)
12-2828.c (F)
0
Figure 13. Receive Gain and Hybrid Balance vs.
Frequency
–10
PSRR (dB)
–20
0
TRANSMIT GAIN
–10
CURRENT
LIMIT
–30
–40
SPECIFICATION RANGE
–50
–60
BELOW
CURRENT
LIMIT
–70
–20
(dB)
–80
10
–30
100
1000
104
105
106
FREQUENCY (Hz)
RETURN LOSS
12-2871.a (F)
–40
–50
100
Figure 16. Typical VBAT Power Supply Rejection
1000
10 4
10 5
FREQUENCY (Hz)
12-2829.b (F)
Figure 14. Transmit Gain and Return Loss vs.
Frequency
Lucent Technologies Inc.
17
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
50
Characteristic Curves (continued)
LOOP CURRENT (mA)
40
OFF-HOOK THRESHOLD LOOP CURRENT
(mA)
25
20
15
30
1
10 kΩ
20
BS = 1,
L7557 BS = 0
L7556
BS = 0
ILIM
–1
Rdc1
10
10
0
0
10
20
5
30
50
40
LOOP VOLTAGE (V)
12-3050.a(F)
0
0
10
20
40
30
50
60
Notes:
VBAT1 = –48 V.
VBAT2 = –28 V.
LOOP CLOSURE THRESHOLD RESISTOR, RLCTH (kΩ)
12-3015 (F)
ILIM = 22 mA.
Rdc1 = 115 Ω.
Note: VBAT = –48 V.
Figure 19. Loop Current vs. Loop Voltage
Figure 17. Loop Closure Program Resistor
Selection
35
LOOP CURRENT (mA)
THRESHOLD RING GROUND CURRENT
(mA)
50
30
25
20
15
40
30
BS = 1,
L7557 BS = 0
L7556
BS = 0
20
10
10
5
0
0
0
0
50
100
150
200
250
RING GROUND CURRENT
DETECTION RESISTOR, RICM (kΩ)
500
1000
1500
2000
LOOP RESISTANCE, RLOOP (W)
12-3051.a(F)
Notes:
VBAT1 = –48 V.
12-3016a (F)
Notes:
Tip lead is open.
VBAT2 = –28 V.
VBAT = –48 V.
Rdc1 = 115 Ω.
Figure 18. Ring Ground Detection Programming
18
ILIM = 22 mA.
Figure 20. Loop Current vs. Loop Resistance
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
PROTECTION RESISTOR MISMATCH (%)
Applications (continued)
Characteristic Curves (continued)
SLIC POWER DISSIPATION (mW)
1500
BS = 1
1000
L7557
BS = 0
500
8
7
49 dB, RP MATCHED TO 1.5 Ω
6
5
4
58 dB,
RP MATCHED
TO 0.5 Ω
3
2
1
0
0
20
L7556
BS = 0
40
80
60
120
100
PROTECTION RESISTOR VALUE (Ω)
12-2559.b (F)
0
0
500
1000
1500
2000
LOOP RESISTANCE, RLOOP (W)
Figure 23. Longitudinal Balance Resistor Mismatch
Requirements
12-3052.a (F)
Notes:
VBAT1 = –48 V.
60
ILIM = 22 mA.
Rdc1 = 115 Ω.
Figure 21. Typical SLIC Power Dissipation vs.
Loop Resistance
2000
LONGITUDINAL BALANCE (dB)
VBAT2 = –28 V.
55
50
45
40
0.0
POWER (mW)
1500
0.5
1.0
1.5
2.0
2.5
PROTECTION RESISTOR MISMATCH (Ω)
12-3021 (F)
1000
Figure 24. Longitudinal Balance vs. Protection
Resistor Mismatch
60 °C/W
500
0
20
40
60
80
100
120
140
160 180
AMBIENT TEMPERATURE, TA (°C)
12-2825.c (F)
Figure 22. Power Derating
Lucent Technologies Inc.
19
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
Region 1; On-hook and low loop currents. The slope
corresponds to the dc resistance of the SLIC, RDC1
(default is 115 Ω typical). The open circuit voltage is the
battery voltage less the overhead voltage of the device,
VOH (default is 7.9 V typical). These values are suitable
for most applications, but can be adjusted if needed.
For more information, see the sections entitled Adjusting dc Feed Resistance or Adjusting Overhead Voltage.
dc Applications
Battery Feed
The dc feed characteristic can be described by:
V B AT – V O H
I L = ---------------------------------R L + 2R P + R dc
VT ⁄ R =
( V BA T – V O H ) × R L
--------------------------------------------
R L + 2R P + R dc
where:
IL = dc loop current.
VT/R = dc loop voltage.
|VBAT| = battery voltage magnitude applied to the power
amplifier stage (VBAT1 or VBAT2).
VOH = overhead voltage. This is the difference between
the battery voltage and the open loop tip/ring
voltage.
RL = loop resistance, not including protection resistors.
RP = protection resistor value.
Rdc = SLIC internal dc feed resistance.
The design begins by drawing the desired dc template.
An example is shown in Figure 25.
LOOP CURRENT (mA)
40
1
10 kΩ
ILIM
–1
Rdc1
10
0
10
20
30
50
40
LOOP VOLTAGE (V)
12-3050.f (F)
Notes:
VBAT1 = –48 V.
VBAT2 = –28 V.
ILIM = 22 mA.
Rdc1 = 115 Ω.
Figure 25. Loop Current vs. Loop Voltage
Starting from the on-hook condition and going through
to a short circuit, the curve passes through two regions:
20
RPROG (kΩ) = 1.67 ILIM (mA)
Switching the Battery
The L7556 and L7557 SLICs provide an input for an
auxiliary battery. Called VBAT2, this power supply
should be lower in magnitude than the primary battery,
VBAT1. Under an acceptable loop condition, VBAT2 can
be switched to provide the loop power through the output amplifiers of the SLIC. The dc template, described
in the last section, is determined by the battery that is
activated—either VBAT1 or VBAT2.
In these applications, the off-hook detector can be
used to indicate when to switch the battery. Just make
sure the off-hook detector will also function as required
with VBAT2 as well as VBAT1.
20
0
Calculate the external resistor as follows:
Which device will be best for you? That mainly
depends on your loop range requirements. If you have
only short loops and no on-hook voltage requirements,
you don't need a battery switch at all. Use the L7551
instead. If you have only to guarantee a short loop
range, e.g., 22 mA into 530 Ω, consider the L7556. The
minimum VBAT2 can be determined by the standard dc
equations.
50
30
Region 2; Current limit. The dc current is limited to a
value determined by external resistor RPROG. This
region of the dc template has a high resistance
(10 kΩ).
Consider an off-hook threshold of 10 mA. This could
represent a 1000 Ω loop with a 48 V VBAT1 active or a
2000 Ω loop with a 28 V VBAT2 active. In this case, if
the loop is below 1000 Ω or above 2000 Ω, off-hook
detection will be accurate. Between 1000 Ω and
2000 Ω, the detector is battery-dependent. This condition must be avoided. In our example, since the maximum loop is 530 Ω, the 10 mA detector is perfectly
acceptable.
If the PTT would like a short loop system that can also
serve long loops, the off-hook detector is not the best
indicator, and better loop intelligence is needed. In this
case, the L7557 can be used. It has an internal comparator that senses when there is enough potential at
VBAT2 to switch without affecting the loop current. In
this case, the loop range is determined by VBAT1, and
VBAT2 is only switched in when the loop is short enough
to use it. This switching is automatic and includes hysteresis to avoid oscillation when the loop length is close
to the VBAT2 switch threshold.
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
VOH
dc Applications (continued)
Overhead Voltage
In order to drive an on-hook ac signal, the SLIC must
set up the tip and ring voltage to a value less than the
battery voltage. The amount that the open loop voltage
is decreased relative to the battery is referred to as the
overhead voltage. Expressed as an equation:
VOH = |VBAT| – (VPT – VPR)
Without this buffer voltage, amplifier saturation will
occur and the signal will be clipped. The device is automatically set at the factory to allow undistorted on-hook
transmission of a 3.17 dBm signal into a 900 Ω loop
impedance. For applications where higher signal levels
are needed, e.g., periodic pulse metering, the 2-wire
port of the SLIC can be programmed with pin DCR.
The drive amplifiers are capable of 4 Vrms minimum
(VAMP). Referring to Figure 26, the internal resistance
has a worst-case value of 46 Ω. So, the maximum signal the device can guarantee is:
Z T/R
V T ⁄ R = 4 V  -----------------------------------------
 Z T/R + 2 ( R P + 46 )
Thus, RP ≤ 35 Ω allows 2.2 Vrms metering signals. The
next step is to determine the amount of overhead voltage needed. The peak voltage at output of tip and ring
amplifiers is related to the peak signal voltage by:
2 ( R P + 40 Ω )
Vamp = V T/R  1 + ------------------------------


ZT ⁄ R
Λ
RP
VT/R
ZT ⁄ R
where VSAT is the combined internal saturation voltage
between the tip/ring amplifiers and VBAT (5.4 V typ.).
RP (Ω) is the protection resistor value, and 40 Ω is the
output series resistance of each internal amplifier.
ZT/R (Ω) is the ac loop impedance.
Example 1, on-hook transmission of a meter pulse:
Signal level: 2.2 Vrms into 200 Ω
35 Ω protection resistors
ILOOP = 0 (on-hook transmission of the metering signal)
2 ( 35 + 40 )
VOH = 5.4 +  1 + ------------------------------ 2 (2.2) = 10.8 V
200
Accounting for VSAT tolerance of 0.5 V, a nominal
overhead of 11.3 V would ensure transmission of an
undistorted 2.2 V metering signal.
Adjusting Overhead Voltage
To adjust the open loop 2-wire voltage, pin DCR is
programmed at the midpoint of a resistive divider from
ground to either –5 V or VBAT. In the case of –5 V, the
overhead voltage will be independent of the battery
voltage. Figure 27 shows the equivalent input circuit to
adjust the overhead voltage.
R1
25 kΩ ± 30%
R2
Λ
+
[ZT/R]
–
2 ( R P + 40 Ω ) Λ
= V S AT +  1 + ------------------------------ V T ⁄ R
DCR
–5 V
40 Ω
12-2562 (F)
+
40 Ω
Figure 27. Equivalent Circuit for Adjusting the
Overhead Voltage
VAMP
–
RP
12-2560.e (F)
Figure 26. SLIC 2-Wire Output Stage
In addition to the required peak signal level, the SLIC
needs about 2 V from each power supply to bias the
amplifier circuitry. It can be thought of as an internal
saturation voltage. Combining the saturation voltage
and the peak signal level, the required overhead can
be expressed as:
Lucent Technologies Inc.
The overhead voltage is programmed by using the following equation:
VOH = 7.9 – 4 VDCR
R 1 || 25 kΩ
= 7.9 – 4  – 5 ×  -------------------------------------- 
R 2 + R 1 || 25 kΩ
R 1 || 25 kΩ
= 7.9 + 20  --------------------------------------
R 2 + R 1 || 25 kΩ
21
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
This is an equivalent circuit for adjusting both the dc
feed resistance and overhead voltage together.
dc Applications (continued)
The adjustments can be made by a simple superposition of the overhead and dc feed equations:
Adjusting dc Feed Resistance
R 1 || 25 kΩ || R 3
V O H = 7.9 + 20  ----------------------------------------------
 R 2 + R 1 || 25 kΩ || R 3
The dc feed resistance may be adjusted with the help
of Figure 28.
R1
RDC
25 kΩ ± 30%
R 1 || 25 kΩ
= 115 Ω + 500 Ω  --------------------------------------
R 2 + R 1 || 25 kΩ
DCR
R3
DCOUT
12-2560 (F)
Figure 28. Equivalent Circuit for Adjusting the dc
Feed Resistance
Rdc
When selecting external components, select R1 on the
order of 5 kΩ to minimize the programming inaccuracy
caused by the internal 25 kΩ resistor. Lower values can
be used; the only disadvantage is the power consumption of the external resistors.
Loop Range
The equation below can be rearranged to provide the
loop range for a required loop current:
∆V D C R
= 115 Ω + 500 Ω -------------------∆V D C O UT
R 1 || 25 kΩ
= 115 Ω + 500 Ω  ----------------------------------
 R 3 + R 1 || 25 kΩ
RL =
The above paragraphs describe the independent setting of the overhead voltage and the dc feed resistance. If both need to be set to customized values,
combine the two circuits as shown in Figure 29.
R1
R2
R3
25 kΩ ± 30%
DCR
–5 V
DCOUT
V BA T – V O H
IL
---------------------------- – 2R P – R d c
Off-Hook Detection
The loop closure comparator has built-in longitudinal
rejection, eliminating the need for an external 60 Hz
filter. The loop closure detection threshold is set by
resistor RLCTH. Referring to Figure 30, NLC is high in
an on-hook condition (ITR = 0, VDCOUT = 0) and
VLCTH = 0.05 mA x RLCTH. The off-hook comparator
goes low when VLCTH crosses zero and then goes negative:
VLCTH = 0.05 mA x RLCTH + VDCOUT
= 0.05 mA x RLCTH – 0.125 V/mA x ITR
RLTCH (kΩ) = 2.5 x ITR (mA)
12-2561 (C)
Figure 29. Adjusting Both Overhead Voltage and dc
Feed Resistance
RP
RL
TIP
+
–
ITR
DCOUT
0.125 V/mA
RLCTH
RING
RP
0.05 mA
+
–
LCTH
NLC
12-2553g(F)
Figure 30. Off-Hook Detection Circuit Applications
22
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
The following example illustrates how the detection circuit of Figure 31 will trip at 12.5 mA dc loop current
using a –48 V battery.
dc Applications (continued)
– 7 – ( – 48 )
IN = ----------------------------2.289 kΩ
= 17.9 µA
Ring Trip Detection
The ring trip circuit is a comparator that has a special
input section optimized for this application. The equivalent circuit is shown in Figure 31, along with its use in
an application using unbalanced, battery-backed ringing.
RLOOP
RC PHONE
RTSP
+
2 MΩ
RTS1
402 Ω
CRTS2
0.27 µF
CRTS1
0.022 µF
IP = IN
IN
RTS2 RTSN
274 kΩ 2 MΩ
V R T SP
= V BAT + I L O O P ( dc ) × R T S 1 + I P × R TS P
Using this equation and the values in the example, the
voltage at input RTSP is –12 V during ringing injection
(ILOOP(dc) = 0). Input RTSP is therefore at a level of 5 V
below RTSN. When enough dc loop current flows
through RTS1 to raise its dc drop to 5 V, the comparator
will trip. In this example,
PHONE
HOOK SWITCH
RTSP
The current IN is repeated as IP in the positive comparator input. The voltage at comparator input RTSP is:
7V
NRDET
+
–
Ring Ground Detection
–
RTSN
15 kΩ
VRING
VBAT
12-3014.f (F)
Figure 31. Ring Trip Equivalent Circuit and
Equivalent Application
The comparator input voltage compliance is VCC to
VBAT, and the maximum current is 240 µA in either
direction. Its application is straightforward. A resistance
(RTSN + RTS2) in series with the RTSN input establishes a
current which is repeated in the RTSP input. A slightly
lower resistance (RTSP) is placed in series with the RTSP
input. When ringing is being injected, no dc current
flows through RTS1, and so the RTSP input is at a lower
potential than RTSN. When enough dc loop current
flows, the RTSP input voltage increases to trip the comparator. In Figure 31, a low-pass filter with a double
pole at 2 Hz was implemented to prevent false ring trip.
Lucent Technologies Inc.
5V
ILOOP(dc) = -----------------402 Ω
= 12.5 mA
Pin ICM sinks a current proportional to the longitudinal
loop current. It is also connected to an internal comparator whose output is pin RGDET. In a ground start
application where tip is open, the ring ground current is
half differential and half common mode. In this case, to
set the ring ground current threshold, connect a resistor RICM from pin ICM to VCC. Select the resistor
according to the following relation:
R I CM ( kΩ ) =
V CC × 228
---------------------I RG ( mA )
The above equation is shown graphically in Figure 18.
It applies for the case of tip open. The more general
equation can be used in ground key application to
detect a common-mode current I CM:
R I C M ( kΩ ) =
V CC × 114
---------------------I CM ( mA )
23
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
Third-Generation Codecs
ac Design
This class of devices includes the gains, termination
impedance, and hybrid balance—all under microprocessor control. Depending on the device, it may or may
not include latches.
There are four key ac design parameters. Termination
impedance is the impedance looking into the 2-wire
port of the line card. It is set to match the impedance of
the telephone loop in order to minimize echo return to
the telephone set. Transmit gain is measured from the
2-wire port to the PCM highway, while receive gain is
done from the PCM highway to the transmit port.
Finally, the hybrid balance network cancels the
unwanted amount of the receive signal that appears at
the transmit port.
At this point in the design, the codec needs to be
selected. The discrete network between the SLIC and
the codec can then be designed. Here is a brief codec
feature and selection summary.
First-Generation Codecs
These perform the basic filtering, A/D (transmit), D/A
(receive), and µ-law/A-law companding. They all have
an op amp in front of the A/D converter for transmit gain
setting and hybrid balance (cancellation at the summing
node). Depending on the type, some have differential
analog input stages, differential analog output stages,
and µ-law/A-law selectability. This generation of codecs
has the lowest cost. They are most suitable for applications with fixed gains, termination impedance, and hybrid balance.
Selection Criteria
In the following examples, use of a first-generation
codec is shown. The equations for second- and thirdgeneration codecs are simply subsets of these. There
are two examples. The first shows the simplest circuit,
which uses a minimum number of discrete components
to synthesize a real termination impedance. The second example shows the use of the uncommitted op
amp to synthesize a complex termination. The design
has been automated in a DOS based program, available on request.
In the codec selection, increasing software control and
flexibility are traded for device cost. To help decide, it
may be useful to consider the following. Will the application require only one value for each gain and impedance? Will the board be used in different countries with
different requirements? Will several versions of the
board be built? If so, will one version of the board be
most of the production volume? Does the application
need only real termination impedance? Does the
hybrid balance need to be adjusted in the field?
Second-Generation Codecs
This class of devices includes a microprocessor interface for software control of the gains and hybrid balance. The hybrid balance is included in the device. ac
programmability adds application flexibility and saves
several passive components and also adds several I/O
latches that are needed in the application. However, it
does not have the transmit op amp, since the transmit
gain and hybrid balance are set internally.
24
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
ac Design (continued)
Selection Criteria (continued)
ac equivalent circuits using a T7513 Codec are shown in Figures 32 and 33.
RX
VGSX
–0.125 V/mA
–
+
ZT/R
RP PT 40 Ω
VS
ZT
AV = 4
+
+ IT/R
VT/R
–
VFXIN
VFXIP
RCVN
–
AV = 1
RT2
–
VITR
RT1
RRCV
RCVP
+
RHB1
VFR
(PWROP)
RG
RP PR 40 Ω
AV = –1
T7513 CODEC
SLIC
12-2554j (F)
Figure 32. ac Equivalent Circuit Not Including Spare Op Amp
ZT5
RX
VGSX
ZT/R
ZT
RP PT 40 Ω
+ IT/R
VT/R
–
RP PR 40 Ω
–0.125 V/mA
+
VITR
RT4
SN
AGND
–
XMT
RT6
+
AV = 4
+
VFXIN
VFXIP
RCVN
–
AV = 1
VS
–
RT3
+
RHB1
RRCV
RCVP
–
VFR
(PWROP)
RGN
AV = –1
SLIC
T7513 CODEC
12-3013b (F)
Figure 33. ac Equivalent Circuit Including Spare Op Amp
Lucent Technologies Inc.
25
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Applications (continued)
Example 2, Complex Termination:
ac Design (continued)
For complex termination, the spare op amp is used
(see Figure 33).
Selection Criteria (continued)
Example 1, Real Termination:
The following design equations refer to the circuit in
Figure 32. Use these to synthesize real termination
impedance.
Termination Impedance:
VT ⁄ R
ZT = -------------–I T ⁄ R
1000
Z T = R P + 80 Ω + ----------------------------------R T1
R T1
1 + --------- + -----------RGP RRCV
Z T5
1000
Z T = 2R P + 80 Ω + ----------------------------------- ( --------- )
R T 3 R T4
RT3
1 + --------- + -----------RGN RRCV
= 2R P + 80 Ω + k ( Z T5 )
8
g rcv = ----------------------------------------------------------------------------RCV
R RCV
ZT
1 + R
-------------- + --------------  1 + ----------

R T3
RGN  
Z T/R
–R X 125 Z T5
g t x = ----------- × ---------- × --------R T6 Z T/R R T4
The hybrid balance equation is the same as in Example 1.
Receive Gain:
VT ⁄ R
grcv = -------------V FR
8
grcv = ------------------------------------------------------------------------------------RCV
R
RCV 
ZT
R
 1 + --------------- + -------------- 1 + -------------

R T1
R GP  
Z T/R
Transmit Gain:
V GSX
gtx = --------------VT ⁄ R
–R X
125
gtx = ----------- x ------------R T2 Z T ⁄ R
Hybrid Balance:
V GSX
hbal = 20log --------------V FR
To optimize the hybrid balance, the sum of the currents
at the VFX input of the codec op amp should be set to
0. The following expressions assume the test network
is the same as the termination impedance.
PCB Layout Information
Make the leads to BGND and VBAT as wide as possible
for thermal and electrical reasons. Also, maximize the
amount of PCB copper in the area of—and specifically
on—the leads connected to this device for the lowest
operating temperature.
When powering the device, ensure that no external
potential creates a voltage on any pin of the device that
exceeds the device ratings. In this application, some of
the conditions that cause such potentials during powerup are the following: 1) an inductor connected to PT
and PR (this can force an overvoltage on VBAT through
the protection devices if the VBAT connection chatters),
and 2) inductance in the V BAT lead (this could resonate
with the VBAT filter capacitor to cause a destructive
overvoltage).
This device is normally used on a circuit card that is
subjected to hot plug-in, meaning the card is plugged
into a biased backplane connector. In order to prevent
damage to the IC, all ground connections must be
applied before, and removed after, all other connections.
RX
hbal = 20log  ------------ – g tx × g rcv
R HB
RX
RHB = ------------------------g tx × g rcv
26
Lucent Technologies Inc.
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Outline Diagram
32-Pin PLCC
Dimensions are in millimeters.
Note: The dimensions in this outline diagram are intended for informational purposes only. For detailed schematics to assist your design efforts, please contact your Lucent Technologies Sales Representative.
12.446 ± 0.127
11.430 ± 0.076
4
PIN #1 IDENTIFIER
ZONE
1
30
5
29
13.970
± 0.076
14.986
± 0.127
13
21
14
20
3.175/3.556
1.27 TYP
0.38 MIN
TYP
SEATING PLANE
0.10
0.330/0.533
5-3813F
Lucent Technologies Inc.
27
L7556, L7557 Low-Power SLICs
with Battery Switch
Data Sheet
January 2000
Ordering Information
Device Part No.
ATTL7556AAU
ATTL7556AAU-TR
ATTL7557AAU
ATTL7557AAU-TR
Description
Low-Power SLIC with Battery Switch
Low-Power SLIC with Battery Switch
Low-Power SLIC with Battery Switch
Low-Power SLIC with Battery Switch
Package
32-Pin PLCC
32-Pin PLCC (Tape and Reel)
32-Pin PLCC
32-Pin PLCC (Tape and Reel)
Comcode
107385668
107749509
107385841
107749517
For additional information, contact your Microelectronics Group Account Manager or the following:
INTERNET:
http://www.lucent.com/micro
E-MAIL:
[email protected]
N. AMERICA: Microelectronics Group, Lucent Technologies Inc., 555 Union Boulevard, Room 30L-15P-BA, Allentown, PA 18103
1-800-372-2447, FAX 610-712-4106 (In CANADA: 1-800-553-2448, FAX 610-712-4106)
ASIA PACIFIC: Microelectronics Group, Lucent Technologies Singapore Pte. Ltd., 77 Science Park Drive, #03-18 Cintech III, Singapore 118256
Tel. (65) 778 8833, FAX (65) 777 7495
CHINA:
Microelectronics Group, Lucent Technologies (China) Co., Ltd., A-F2, 23/F, Zao Fong Universe Building, 1800 Zhong Shan Xi Road, Shanghai
200233 P. R. China Tel. (86) 21 6440 0468, ext. 316, FAX (86) 21 6440 0652
JAPAN:
Microelectronics Group, Lucent Technologies Japan Ltd., 7-18, Higashi-Gotanda 2-chome, Shinagawa-ku, Tokyo 141, Japan
Tel. (81) 3 5421 1600, FAX (81) 3 5421 1700
EUROPE:
Data Requests: MICROELECTRONICS GROUP DATALINE: Tel. (44) 7000 582 368, FAX (44) 1189 328 148
Technical Inquiries: GERMANY: (49) 89 95086 0 (Munich), UNITED KINGDOM: (44) 1344 865 900 (Ascot),
FRANCE: (33) 1 40 83 68 00 (Paris), SWEDEN: (46) 8 594 607 00 (Stockholm), FINLAND: (358) 9 4354 2800 (Helsinki),
ITALY: (39) 02 6608131 (Milan), SPAIN: (34) 1 807 1441 (Madrid)
Lucent Technologies Inc. reserves the right to make changes to the product(s) or information contained herein without notice. No liability is assumed as a result of their use or application. No
rights under any patent accompany the sale of any such product(s) or information.
Copyright © 2000 Lucent Technologies Inc.
All Rights Reserved
January 2000
DS00-060ALC (Replaces DS97-172ALC)