AN-151 FXO/DAA Design Using IXYS Integrated Circuits Division

INTEGRATED CIRCUITS DIVISION
Application Note: AN-151
FXO/DAA Design
Using IXYS Integrated Circuits Division
OptoMOS® Components
AN-151-R02
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1
Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
1. Introduction
2.2 DAA Functions
IXYS Integrated Circuits Division OptoMOS components can be applied to a variety of DAA telephone
line interface designs suitable for many applications.
This application note includes a collection of DAA circuits that use IXYS Integrated Circuits Division
OptoMOS components. It also includes a primer on
DAA circuit fundamentals and listings of OptoMOS
DAA design resources.
These circuits show the versatility of the OptoMOS
line of components. You can select just the portions of
a DAA you need to use, and select the level of integration required to minimize component count, cost, and
printed-circuit board space.
Note: Circuits presented in this application note
assume a +5 Vdc power supply.
1.
2.
3.
4.
5.
Line termination
2-to-4 wire conversion (hybrid function)
Ring detection
Signal coupling
Monitoring on-hook transmissions (display functions like caller-ID)
6. Surge/transient protection
2.2.1 Surge Protection
The surge protection block protects the CPE from
damage, most likely lightning induced transients or
power-cross events. Protection circuit topology varies
and is determined by the system’s reliability criteria.
2.2.2 Switchhook
The switchhook controls the off-hook and on-hook
condition. When the switchhook is closed, the device
is off-hook and current flows from the central office
battery through the switchhook and DC termination
circuit. This current is known as the loop current.
2. DAA Fundamentals
2.1 Telephone Network Connection
Devices that connect to telephone networks generally
require a data access arrangement circuit (DAA). The
DAA provides the physical connection between the
telephone line and the device, while, at the same time,
providing the necessary electrical isolation that allows
devices designed with it to meet the requirements of
applicable regulatory agencies. Examples of some
common devices are telephones and modems found
in set-top boxes, point-of-sale terminals, answering
machines, vending equipment, and metering equipment.
Isolation of host equipment from the telephone network assures that no harm to the network occurs due
to a device malfunction in the customer premises
equipment (CPE). Without isolation, a device connected to the network could damage central office
equipment and endanger telephone company personnel if it failed. Additionally, if a high voltage transient is
applied to the telephone line from an outside source (a
lightning-induced transient, for example), the device
and user are generally protected by the high electrical
isolation that a DAA provides.
2
In addition to the primary function of isolation, a DAA
circuit must also provide the following functions while
meeting stringent regulatory requirements:
2.2.3 DC Termination
The DC termination presents a low DC resistance
across tip and ring when the DAA is off-hook, but
maintains a very high AC impedance that will not interfere with the AC termination of the DAA. The DC termination also has a bridge rectifier that allows the
circuit to operate even if the tip and ring leads are
inadvertently reversed.
2.2.4 Ring Detection
The ring detection block connects across the tip and
ring terminals and is used to monitor the line for an
incoming ring signal. The circuit is AC coupled in order
to meet low on-hook current draw requirements. The
ring detection circuit requires an isolation barrier to
isolate the telephone line from the CPE power supply.
2.2.5 Isolation and Signal Coupling
The isolation and signal coupling block couples the AC
signal to and from the host system while maintaining
linearity and providing electrical isolation in excess of
1500 VRMS.
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
2.2.6 Hybrid
2.3.2 Display Services (Caller ID)
The hybrid network is also known as the 2-to-4 wire
converter. Since both transmit and receive signals are
on the same telephone line pair at the same time (full
duplex), a mechanism is required such that the transmitted signal from the device is removed or minimized
at the device receive path. In a voice application, poor
rejection of the transmit signal into the receive path is
apparent as “talker echo.” For data applications, poor
rejection of the transmit signal in the receive path can
cause poor data throughput. The loss from transmit
path to receive path is known as transhybrid loss,
measured in decibels.
2.3 Optional DAA Circuits
Display services such as caller ID require monitoring
the telephone line in the on-hook state. The establishment of an on-hook AC path for display services signals is shown in the Caller ID Detection section
(Section 4.2 on page 12).
2.3.3 Line Use Detection
Managing the use of the telephone line in either the
on-hook or off-hook states can be a DAA requirement
for some CPE devices. See the 911 Function section
(Section 5.1 on page 14), and the APOH Function
section (Section 5.2 on page 16) for more information.
2.3.4 Reverse Battery Condition
In addition to the basic functions described above,
DAA circuits may be required to perform one or more
of these optional functions:
2.3.1 Loop Current Detection
Some PBX systems require reading the current being
drawn from the phone line. Using a DAA to detect loop
current is shown in the Loop Current Detection section
(Section 4.1 on page 10).
Some telephone networks, especially private ones,
use reverse-battery type signalling for direct-inwarddialing (DID). A reverse battery detection circuit is
shown in the Detecting Loop Reverse-Battery Condition on a Telephone Line section (Section 7 on page
20).
2.4 DAA Circuits
• North American/JATE DAAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Using 1-Form-A Switchhook - LCA110 and LDA101 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Using TS117 for Switchhook and Ring Detect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Using ITC135 or ITC137 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
• DAA Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Loop Current Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Caller ID Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
• Phone Line Use Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
911 Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
APOH Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
• DAA Hybrid Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
• Detecting Loop Reverse-Battery Condition on a Telephone Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
• European Type DAA Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
European Type DAA with Metering Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
DAA for Spain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
• Circuit Layout Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
• OptoMOS Design Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
AN-151-R02
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
3. North American/JATE DAAs
3.1 Using 1-Form-A Switchhook - LCA110 and LDA101
Figure 1 shows a basic DAA implementation using IXYS Integrated Circuits Division’s LCA110 (or CPC1035) as the
switchhook and LDA101 as the ring detector.
Figure 1. North American/JATE DAA Using OptoMOS LDA101 and LCA110
Vcc
R6
OH
N.C. 3
2
1
U1
LCA110
F1
4
5
TIP
6
1.25A//250V
C1
R2
6
HYBRID
HYBRID
CIRCUIT
CIRCUIT
ZD3
C4
1
R1
BR1
RING
R3
ZD4
ZD2
U2
LDA101
Vcc
C2
+
Q1
ZD5
ZD1
D1
5
2
4
3
Z
T1
SP1
C3 +
R4
R5
RING
On asserting OH, loop current flows through the solid-state relay and the electronic gyrator circuit consisting of BR1,
Q1, R3, R4, R5, ZD5, and C3. The gyrator presents a high AC impedance while providing a low DC resistance so that
DC loop current can flow. Signals are AC coupled through C2 and T1 to the hybrid circuit.
U2, an LDA101, and it’s associated components provide half-wave ring detection. The LDA101 has one internal LED
that emits light during one-half of the ringing AC sine wave. Full-wave ring detection can be used by substituting an
LDA100 for U2 and removing D1. The LDA100 has back-to-back LEDS that emit light on both halves of the sine wave.
In this circuit, D1 prevents high reverse voltages from damaging the LED in U2. C1 AC couples the ringing signal to
the ring detector. ZD1 and ZD2 prevent in-band signals (modem tones or speech) from falsely triggering RING. SP1
and the optional fuse provide circuit protection.
This DAA design, while simple, can support high modem throughput rates up to V.90 with proper selection of discrete
components and good printed-circuit board design practices.
4
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
Table 1: Part List for Figure 1
Quantity
Reference Designator
Description
1
R1
47 k, 1/8 W
1
R2
8.2 k, 1/4 W
1
R3
68 k, 1/4 W
1
R4
100 k, 1/4 W
1
R5
10 , 1/4 W
1
R6
470 , 1/4 W
1
C1
0.47 F, 250 V
1
C2
10 F, 50 V, Tantalum
1
C3
10 F, 25 V, Tantalum
1
C4
optional (see Section 6 on page 18)
1
T1
Midcom 82096 transformer
1
BR1
400 PIV bridge rectifier
1
U1
IXYS Integrated Circuits Division LCA110
1
U2
IXYS Integrated Circuits Division LDA101
2
ZD1, ZD2
18 V Zener diode
2
ZD3, ZD4
5.1 V Zener diode
1
ZD5
18 V, 1/2 W Zener diode
1
Q1
FZT605 Zetex Darlington
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
1
D1
1N4001
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
3.2 Using TS117 for Switchhook and Ring Detect
Figure 2 shows a higher level of integration, where an IXYS Integrated Circuits Division TS117 takes the place of the
LCA110 and LDA101 in Figure 1. The TS117 provides switchhook and ring detect functions with the same external
components used in Figure 1.
The TS117 has two back-to-back LEDs for use in the ring detector. With D1 installed the circuit provides half-wave
ring detection. With D1 removed the circuit provides full-wave ring detection.
Figure 2. North American/JATE DAA Using OptoMOS TS117
Vcc
R1
R6
OH
Vcc
RING
4
3
2
1
U1
TS117
5
6
7
8
F1
TIP
1.25A/250V
C1
R2
T1
ZD1
ZD3
C4
D1
BR1
Z
HYBRID
CIRCUIT
ZD2
C2
+
SP1
R3
ZD4
Q1
ZD5
C3 +
R4
R5
RING
6
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
Table 2: Part List for Figure 2
Quantity
Reference Designator
Description
1
R1
47 k, 1/8 W
1
R2
8.2 k, 1/4 W
1
R3
68 k, 1/4 W
1
R4
100 k, 1/4 W
1
R5
10 , 1/4 W
1
R6
470 , 1/4 W
1
C1
0.47 F, 250 V
1
C2
10 F, 50 V, Tantalum
1
C3
10 F, 25 V, Tantalum
1
C4
optional (see Section 6 on page 18)
1
T1
Midcom 82096 transformer
1
BR1
400 PIV bridge rectifier
1
U1
IXYS Integrated Circuits Division TS117
2
ZD1, ZD2
18 V Zener diode
2
ZD3, ZD4
5.1 V Zener diode
1
ZD5
18 V, 1/2 W Zener diode
1
Q1
FZT605 Zetex Darlington
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
1
D1
1N4001
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
3.3 Using ITC135 or ITC137
Figure 3 shows even more integration, using the IXYS Integrated Circuits Division ITC135 or ITC137.
The ITC135 and ITC137 include the switchhook function, a Darlington transistor for the gyrator circuit, an optocoupler
for ring detect, and transient protection zener diodes. The ITC135 offers half-wave ring detect, while the ITC137 offers
full-wave ring detect. All the discrete components function as described previously.
This DAA design saves printed-circuit real estate.
Figure 3. North American/JATE DAA Using OptoMOS ITC135 or ITC137
U1
OH
T1
HYBRID
CIRCUIT
C4
C2
+
1
R6
Vcc
ITC135 / ITC137
F1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
C3
+
TIP
C1
R5
R2
R3
R4
ZD2
D1
ZD1
SP1
RING
Vcc
R1
RING
8
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INTEGRATED CIRCUITS DIVISION
Table 3: Part List for Figure 3
Quantity
Reference Designator
Description
1
R1
47 k, 1/8 W
1
R2
8.2 k, 1/4 W
1
R3
51 k, 1/4 W
1
R4
22 k, 1/4 W
1
R5
10 , 1/4 W
1
R6
470 , 1/4 W
1
C1
0.47 F, 250 V
1
C2
10 F, 50 V, Tantalum
1
C3
10 F, 25 V, Tantalum
1
C4
optional (see Section 6 on page 18)
1
T1
Midcom 82096 transformer
1
U1
IXYS Integrated Circuits Division ITC135 or ITC137
2
ZD1, ZD2
18 V Zener diode
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
4. DAA Options
4.1 Loop Current Detection
Loop current detection can be implemented with any of the DAA circuits presented previously. Figure 4 shows a loop
current detection circuit using the DAA circuit shown in Figure 3.
Figure 4. Loop Current Detection Using LDA100
U1
T1
HYBRID
CIRCUIT
C2
+
R6
Vcc
C4
1
ITC135/ITC137
2
15
3
14
4
13
5
12
6
11
7
10
8
9
-RING
R1
F1
16
Tip
+
C3
R5
R3
1.25/250V
C1
R2
R4
ZD2
D1
ZD1
Z
-OH
SP1
Vcc
R7
3
2
Vcc
R8
Ring
1
U2
LDA100
4
5
6
-LOOP
In this circuit, an IXYS Integrated Circuits Division LDA100 optocoupler (U2) is connected in series with the RING lead
after the surge protector. When the DAA goes off hook, current flows through one of the LEDs in the LDA100. The
LDA100 was chosen because it can be used to sense loop current regardless of the direction of loop current flow.
Select the value of R7 to match your requirement for the minimum loop current to detect. The minimum forward voltage of the LEDs in the LDA100 is 0.9 V. To set the value of R7 for 15 mA, use:
VF
- = 60
R7 = ------------15mA
In this circuit it is important to size R8 according to the current transfer ratio information given in the LDA100 data
sheet. The part list in Table 4 shows component values for a typical loop current detection of 15 mA.
10
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
Table 4: Part List for Figure 4
Quantity
Reference Designator
Description
2
R1, R8
47 k, 1/8 W
1
R2
8.2 k, 1/4 W
1
R3
51 k, 1/4 W
1
R4
22 k, 1/4 W
1
R5
10 , 1/4 W
1
R6
470 , 1/4 W
1
R7
60 , 1/4 W
1
C1
0.47 F, 250 V
1
C2
10 F, 50 V, Tantalum
1
C3
10 F, 25 V, Tantalum
1
C4
optional (see Section 6 on page 18)
1
T1
Midcom 82096 transformer
1
U1
IXYS Integrated Circuits Division ITC135 or ITC137
1
U2
IXYS Integrated Circuits Division LDA100
2
ZD1, ZD2
18 V Zener diode
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
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INTEGRATED CIRCUITS DIVISION
4.2 Caller ID Detection
Figure 5 shows an ITC135/ITC137-based DAA like the one in figure 3 with the addition of a TS117 to handle loop current detection and caller ID (CID) signal processing. For CID processing without loop current detection, substitute
CPC1035 or LCA110 for the TS117.
CID signals must be passed by the DAA while the DAA is on-hook. Voice-band FSK CID signals are included after the
first ring burst.
This circuit uses the relay portion of the TS117 to pass CID signals as follows:
1. The host processor detects the first ring burst from the RING output of the ITC135/ITC137.
2. The host processor asserts CID after the first ring, completing an AC signal path from C1 through the relay in the
TS117, and coupling the CID signal through the transformer and hybrid to the CODEC or data pump.
3. After receiving the CID signal, the host processor de-asserts CID, preserving on-hook telephone line characteristics.
Figure 5. Caller ID Detection Using TS117
T1
HYBRID
CIRCUIT
1
C2
+
R6
Vcc
C4
U1
ITC135/ITC137
2
15
3
14
4
13
5
12
6
11
7
10
8
9
RING
F1
16
TIP
1.25A/250V
+
C3
C1
R5
R2
R3
R4
ZD2
D1
ZD1
Z
OH
SP1
Vcc
R1
Vcc
CID
R9
LOOP
R8
Vcc
12
U2
TS117
RING
1
8
2
7
3
6
4
5
R7
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INTEGRATED CIRCUITS DIVISION
Table 5: Part List for Figure 5
Quantity
Reference Designator
Description
2
R1, R8
47 k, 1/8 W
1
R2
8.2 k, 1/4 W
1
R3
51 k, 1/4 W
1
R4
22 k, 1/4 W
1
R5
10 , 1/4 W
1
R6
470 , 1/4 W
1
R7
60 , 1/4 W
1
C1
2.2 F, 50 V
1
C2
10 F, 50 V, Tantalum
1
C3
10 F, 25 V, Tantalum
1
C4
optional (see Section 6 on page 18)
1
T1
Midcom 82096 transformer
1
U1
IXYS Integrated Circuits Division ITC117P
1
U2
IXYS Integrated Circuits Division ITC135/ITC137
2
ZD1, ZD2
18 V Zener diode
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
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5. Phone Line Use Detection
DAA circuits may need help managing the use of the telephone line to which they are connected by monitoring for
another parallel-connected telephone off-hook while the modem is in either the off-hook or on-hook states. These
functions are often called the 911 function (monitoring for another telephone going off-hook while the DAA is off-hook)
and another phone off-hook or APOH (monitoring for another phone using the line while the DAA is on-hook).
Bear in mind that these are two similar but different situations that must be handled differently in the DAA.
5.1 911 Function
Consider the case of the satellite set-top box. The STB periodically dials out to transfer information with the service
provider. During this call, other devices (like telephones) connected to the telephone line cannot be used until the
information transfer concludes and the DAA in the STB hangs up. This leads to the potentially dangerous situation
where an emergency occurs during this period where the user needs to dial “911.” The DAA in the STB must have the
capability to detect when another phone or device tries to use the telephone line while the STB is already using the
line.
Figure 6 shows an IXYS Integrated Circuits Division OptoMOS DAA with a 911 function detector.
Figure 6. 911 Function
BR+
BR-
U1
OH
T1
HYBRID
CIRCUIT
C2
1
R6
+
Vcc
C6
ITC135/ITC137
TIP
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
+
F1
C1
C3
R5
R2
R4
R3
ZD2
SP1
D1
ZD1
RING
Vcc
R1
Q1
BR+
RING
U2
LDA100
R10
1
6
2
5
3
4
Vcc
C4
R9
R7
D2
C5
+
911
R8
BR-
With the DAA off-hook, capacitor C5 charges through the PN emitter-base junction of transistor Q1. With Q1 on, current flows through the LED in U2, holding the 911 output off.
When another phone tries to use the telephone line, the tip to ring voltage drops, causing the base and emitter voltages of Q1 to drop. With D2 now reverse-biased, the charge in capacitor C5 maintains the previous off-hook voltage
level on the cathode of D2 momentarily. Q1 turns off, shutting off the LED in U2, and causing a logic high pulse at the
911 output. After C5 discharges through R8, Q1 conducts, the LED in U2 turns on, and the 911 output returns low.
The width of the output pulse is determined by the time constant of C5 and R8.
The system controller must detect this pulse and tell the DAA to release the telephone line (go on-hook).
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INTEGRATED CIRCUITS DIVISION
Table 6: Part List for Figure 6
Quantity
Reference Designator
Description
2
R1, R9
47 k, 1/8 W
1
R2
8.2 k, 1/4 W
1
R3
51 k, 1/4 W
1
R4
22 k, 1/4 W
1
R5
10 , 1/4 W
1
R6
470 , 1/4 W
1
R7
1 k, 1/4 W
2
R8, R10
10 k, 1/4 W
1
C1
0.47 F, 50 V
1
C2
10 F, 50 V, Tantalum
1
C3
10 F, 25 V, Tantalum
1
C4
0.1 F, 50 V
1
C5
10 F, 16 V
1
C6
optional (see Section 6 on page 18)
1
T1
Midcom 82096 transformer
1
U1
IXYS Integrated Circuits Division ITC135/ITC137
1
U2
IXYS Integrated Circuits Division LDA100
1
D1
1N4001
2
ZD1, ZD2
18 V Zener diode
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
5.2 APOH Function
While the 911 DAA function allows for release of a phone line when a parallel-connected phone is taken off-hook (see
Section 5.1 on page 14), another circuit is required to see if another device has taken the phone line off-hook before
the DAA tries to connect. This function is often called APOH (another phone off-hook).
An APOH circuit can take advantage of the voltage drop that occurs on a telephone line when any parallel-connected
device takes the line off-hook. In North America, for instance, the tip to ring voltage difference is usually greater than
40 Vdc when the telephone is not in use, but, when the line is in use, the tip to ring voltage is somewhere between 4
to 11 Vdc.
Figure 7 shows an IXYS Integrated Circuits Division OptoMOS DAA with an APOH detector.
Figure 7. APOH Detection Using TS117
U1
T1
HYBRID
CIRCUIT
C2
+
1
R6
Vcc
C4
ITC135/ITC137
F1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
+
C3
C1
TIP
ZD3
ZD4
R5
R2
R3
R7
R4
ZD2
D1
ZD1
Z
OH
SP1
RING
Vcc
R1
Vcc
U2
TS117
RING
R8
CHK_LINE
Vcc
R9
APOH
To check whether or not the line is in use, the system controller asserts CHK_LINE, closing the relay portion of U2, an
IXYS Integrated Circuits Division TS117. ZD3 and ZD4 prevent current flow in this part of the circuit when the tip to
ring voltage drops between 4 to 11 Vdc. Two 18 V Zener diodes prevent current flow and make the circuit insensitive
to telephone line polarity.
With another telephone device offhook, no current flows through the APOH branch of the circuit, turning the optocoupler in U2 off. This sets the APOH output high, indicating an APOH condition. With no external telephone devices offhook the Zeners conduct. Current in the APOH detector circuit causes APOH to go low. With APOH low, the host
device can assert OH and use the telephone line.
Selecting the value of R7 is critical. R7 must be a high enough value to reduce telephone line loop current below the
threshold normally considered as an off-hook condition by the central office equipment. Yet R7 must also be a low
enough value to provide sufficient current to the optocoupler in U2 to keep it on when there is not another parallelconnected telephone off-hook.
After checking the line for APOH, the system controller must de-assert CHK_LINE for normal DAA operation. See
IXYS Integrated Circuits Division’s application note AN-123, Using CYG2911 and TS117 in APOH (911) Circuits for
more information on component value selection.
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
Table 7: Part List for Figure 7
Quantity
Reference Designator
Description
2
R1, R9
47 k, 1/8 W
1
R2
8.2 k, 1/4 W
1
R3
51 k, 1/4 W
1
R4
22 k, 1/4 W
1
R5
10 , 1/4 W
1
R6
470 , 1/4 W
1
R7
51 k, 1/4 W
1
R8
470 , 1/4 W
1
C1
0.47 F, 250 V
1
C2
10 F, 50 V, Tantalum
1
C3
10 F, 25 V, Tantalum
1
C4
0.1 F, 50 V
1
C5
10 F, 16 V
1
C6
optional (see Section 6 on page 18)
1
T1
Midcom 82096 transformer
1
U1
IXYS Integrated Circuits Division ITC135/ITC137
1
U2
IXYS Integrated Circuits Division TS117
2
ZD1, ZD2, ZD3, ZD4
18 V Zener diode
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
1
D1
1N4001
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
6. DAA Hybrid Circuit
Figure 8 shows a typical hybrid (two-wire to four-wire conversion) circuit. The signal labelled TX in the diagram is the
signal transmitted from the CODEC or modem data pump to the telephone line.
Figure 8. Typical Hybrid Circuit
R1
Tx
R2
2
3
Vcc
-
U1A
C2 T1
R4
1
+
R5
R3
To DAA Front-End/ Phone
Line
U1C
R9
C1
4
9
R6
8
Vcc/2
R10
13
U1B
Rx
+
7
-
5
6
R7
R8
The signal is amplified by U1A to account for the transducer loss incurred through R4 and T1, typically 6 dB when
connected to a properly matched 600  line. The value of R4 is determined by the specific transformer in use and
often specified by the transformer manufacturer.
U1C is a low output-impedance buffer that reproduces the voltage at pin 9. R8 and R9 are matched so that the reference Voltage VCC/2 allows hybrid operation from a single supply.
U1 is specified as a rail-to-rail amplifier to accommodate large signal swings.
R5 and R6 present part of the transmit signal to U1B. This signal cancels the transmit signal (V1) from the receive
path in U1B as follows:
R8
R7 + R8 R6
V RX =  --------------------  ------- V1 –  ------- V2
 R7
 R5 + R6  R7
Using the values from the part list for the circuit in figure 8, where R7 = 20 k, R8 = 40 k, R5 = 15 k, and R6 = 15
k, the formula becomes:
V RX =  1.5   V1  –  2   V2 
Setting VRX for 0, with no transmitted signal appearing at RX yields:
0 =  1.5   V1  –  2   V2 
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
Solving for V2 in terms of V1 yields:
1.5
V2 =  -------  V1 
 2
Substituting into the original equation yields:
1.5
V RX =  1.5   V1  –  2   -------  V1  = 0
 2
While this equation shows complete cancellation of the transmit signal in the receive path, practical considerations,
such as component tolerances and variations in telephone line length, suggest a real-world cancellation of between
15 dB to 30 dB.
Capacitor C2 compensates for leakage inductance effects from the transformer at high frequencies. This capacitor
may improve or degrade transhybrid loss, depending on the transformer. Test the circuit to optimize the value for C2
for transhybrid loss.
Table 8: Part List for Figure 8
Quantity
Reference Designator
Description
1
R1
20 k, 1/8 W
1
R2
10 k, 1/4 W
1
R3
6.8 k, 1/4 W
1
R4
530 , 1/4 W
2
R5, R6
15 k, 1/4 W
1
R7
20 k, 1/4 W
1
R8
40 k, 1/4 W
2
R9, R10
47 k, 1/4 W
1
C1
0.1 F, 50 V
1
C2
see text
1
U1
TS 925 op amp, ST Microelectronics or similar
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
7. Detecting Loop Reverse-Battery Condition on a Telephone Line
Some equipment connected to telephone networks must be able to detect reversal of the battery feed voltage. Some
direct-inward-dialing (DID) systems use loop reverse-battery signalling. See ANSI T1.405-1996 for more information.
One requirement of loop reverse-battery condition detectors is the ability to distinguish the direction of battery current.
Figure 9 shows a loop reverse-battery detection circuit using an IXYS Integrated Circuits Division LDA201 that provides forward and reverse output signals.
Figure 9. Loop Reverse-Battery Detection Using LDA201
VCC
LDA201
R
1
8
2
7
3
6
4
5
R
REVERSE
FORWARD
RSENSE
Data Access
Arrangement
Protection
Telephone
Line
Tip is normally positive with respect to ring in telephone loops. The nominal open voltage from the telephone network
is -48 Vdc. In this circuit, the value of RSENSE allows a threshold current before forward or reverse sensing.
Given the nominal forward voltage of the LEDs in the LDA201 of 1.2 V, a value of 120  for RSENSE provides a
10 mA threshold value, where
V
R SENSE = -----FI
or,
1.2 - = 120
R SENSE = ------------10mA
When loop current exceeds 10 mA with normal polarity, FORWARD is asserted. When the loop current exceeds
10 mA with reversed polarity, REVERSE is asserted. The forward voltage specification for the LDA201 varies from 0.9
V to 1.4 V and is affected by temperature. With RSENSE at 120 , detection threshold currents will vary from 7.5 mA to
11.7 mA.
Set the values of the pull-up resistors (R) based on the minimum current transfer ratio of the LDA201 and the minimum LED current for the application according the specifications in the LDA201 data sheet.
The LEDs in the LDA201 are rated for 100 mA maximum current, so current limited resistors in series with the LEDs
are not needed.
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AN-151-R02
Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
8. European Type DAA Circuits
The circuit in Figure 10 can be populated for many of the telephone systems that require compliance to European
Directive 1999/5/EC from March 9, 1999 and the now obsolete TBR-21. Diagrams are also included here for specific
implementations required in certain areas.
The IAA110P was chosen for this design because it can function as the switchhook, ring detector, and as a mute
relay.
Figure 10. European Type DAA Using IAA110P
Vcc
RING
OH
MUTE
Vcc
R6
R7
R8
8
7
6
5
4
3
2
1
U1
IAA110P
F1 TIP
9
10 11 12 13 14 15 16
1.25A//250V
C1
R1
R2
T1
C4
ZD2
C2
+
ZD1
ZD3
D1
D5
ZD4
Z
HYBRID
CIRCUIT
SP1
R4
Q1
C3+
R5
R3
R3
Q2
RING
The mute relay can be used both for low-impedance (fast) pulse dialing and to meet the transient off-hook requirements of some systems. Typically, MUTE is asserted in conjunction with OH and held for 50 milliseconds.
One important functional difference between this circuit and the circuits described earlier is telephone line loop-current limiting. Many European systems require limiting the loop current to 60 mA.
Loop current limiting is accomplished with Q2 and R3 in this circuit. With R3 set to 10  and the VBE of Q2 of 0.6 V,
line current is limited to 60 mA.
Limiting the current in this way leads to the possibility of tip to ring voltages as high as 40 V, which infers that power
dissipation in Q1 could be as high as 2.4 Watts. Q1 requires adequate heat sinking to account for this high power
level.
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
Table 9: Part List for Figure 10
Quantity
Reference Designator
Description
1
R1
20 k, 1/4 W
1
R2
100 k, 1/8 W
1
R3
10 , 1/8 W
1
R4
47 k, 1/8 W
1
R5
68 k, 1/8 W
2
R6, R7
470 , 1/8 W
1
R8
47 k, 1/8 W
1
C1
0.33 F, 250 V
1
C2
10 F, 50 V Tantalum
1
C3
10 F, 25 V Tantalum
1
C5
optional (see Section 6 on page 18)
1
T1
Midcom 82096 transformer
1
U1
IXYS Integrated Circuits Division IAA110P
2
ZD1, ZD2
33 V Zener
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
1
D2
1N4001
1
BR1
400 V bridge rectifier
1
Q1
FZT604 NPN Darlington, Zetex
1
Q2
BC846 NPN Transistor, 65 V
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AN-151-R02
Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
8.1 European Type DAA with Metering Filter
Some areas, like Germany, use telephone service metering signals to collect billing information. The circuit in Figure
11 is similar to the one in Figure 10, but adds an LC tank circuit at the tip connection to filter out the metering signal
(16 kHz in the case of Germany) and preserve DAA DC characteristics while off-hook.
Figure 11. TBR-21 Type DAA With Metering Filter Using IAA110P
Vcc
MUTE
RING
OH
R6
Vcc
R7
R8
8
7
6
5
4
3
2
1
U1
IAA110P
F1 TIP
L1
9
10 11 12 13 14 15 16
1.25A//250V
C1
C6
R1
R2
C5
ZD2
C2
+
ZD3
R9
ZD4
C4
ZD1
D2
D5
Z
T1
HYBRID
CIRCUIT
SP1
R4
D1
R11
C3+
Q1
R5
R3
RING
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
Table 10: Part List for Figure 11
Quantity
Reference Designator
Description
1
R1
20 k, 1/4 W
1
R2
100 k, 1/8 W
1
R3
10 , 1/8 W
1
R4
120 k, 1/8 W
1
R5
68 k, 1/8 W
2
R6, R7
470 , 1/8 W
1
R8
47 k, 1/8 W
1
R9
180 , 1/4 W
1
R11
68 , 1/4 W
1
C1
0.47 F, 250 V
1
C2
10 F, 50 V Tantalum
1
C3
10 F, 25 V Tantalum
1
C4
0.082 F, 50 V
1
C5
optional (see Section 6 on page 18)
1
C6
0.29 F, 50 V
1
T1
Midcom 82096 transformer
1
U1
IXYS Integrated Circuits Division IAA110P
1
L1
3.3 mH inductor, 100 mA dc current
2
ZD1, ZD2
20 V Zener
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
1
L1
3.3 mH inductor, 100 mA
1
D1
8.2 V Zener, 1/4 W
1
D2
1N4001
1
BR1
400 V bridge rectifier
1
Q1
FZT604 NPN Darlington, Zetex
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
8.2 DAA for Spain
Figure 12 uses a circuit similar to Figure 11, but includes components needed for regulatory compliance in Spain as
of the date of publication.
Figure 12. DAA for Spain Using IAA110P
Vcc
RING
MUTE
R6
R8
OH
Vcc
R7
8 7 6 5 4 3
2 1
U1
IAA110P
F1 TIP
9 10 11 12 13 14 15 16
1.25A//250V
C1
R1
R2
C5
ZD2
C2
+
ZD3
R9
ZD4
C4
ZD1
D2
BR1
R4
Z
T1
HYBRID
CIRCUIT
SP1
D1
C3
Q1
+
R5
Q2
R3
RING
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Application Note: AN-151
INTEGRATED CIRCUITS DIVISION
Table 11: Part List for Figure 12
Quantity
Reference Designator
Description
1
R1
10 k, 1/4 W
1
R2
100 k, 1/8 W
1
R3
10 , 1/8 W
1
R4
68 k, 1/8 W
1
R5
100 k, 1/8 W
2
R6, R7
470 , 1/8 W
1
R8
47 k, 1/8 W
1
R9
820 , 1/8 W
1
C1
0.47 F, 250 V
1
C2
10 F, 50 V Tantalum
1
C3
10 F, 25 V Tantalum
1
C4
0.056 F, 50 V
1
C5
optional (see Section 6 on page 18)
1
T1
Midcom 82096 transformer
1
U1
IXYS Integrated Circuits Division IAA110P
2
ZD1, ZD2
33 V Zener
1
SP1
P3100SB Teccor surge suppressor
1
F1
1.25 A, 250 V fuse
1
D1
8.2 V Zener, 1/4 W
1
D2
1N4001
1
BR1
400 V bridge rectifier
1
Q1
FZT604 NPN Darlington, Zetex
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INTEGRATED CIRCUITS DIVISION
Application Note: AN-151
9. Circuit Layout Considerations
IXYS Integrated Circuits Division strongly recommends that engineers designing a DAA circuit using OptoMOS components become familiar with all regulatory and safety requirements for such devices. In particular, IEC950 and
UL1950 contain relevant and useful information. FCC part 68.3, TBR-21, and ETSI EG201 121 also provide useful
information.
Although written specifically for IXYS Integrated Circuits Division’s LITELINKTM products, application note AN-146,
Guidelines for Effective LITELINK Designs, contains information useful to the OptoMOS DAA designer.
Remember that component placement and printed-circuit board layout are critical to building compliant, safe products.
10. OptoMOS Design Resources
IXYS Integrated Circuits Division’s web site has a wealth of information useful for designing with its products, including
application notes and reference designs. Product data sheets also contain additional application and design
information. See the following links:
Application Note AN-114: IITC117P Integrated Telecom Circuit.
For additional information please visit our web site at: www.ixysic.com
IXYS Integrated Circuits Division makes no representations or warranties with respect to the accuracy or completeness of the contents of this publication and
reserves the right to make changes to specifications and product descriptions at any time without notice. Neither circuit patent licenses or indemnity are expressed
or implied. Except as set forth in IXYS Integrated Circuits Division’s Standard Terms and Conditions of Sale, IXYS Integrated Circuits Division assumes no liability
whatsoever, and disclaims any express or implied warranty relating to its products, including, but not limited to, the implied warranty of merchantability, fitness for a
particular purpose, or infringement of any intellectual property right.
The products described in this document are not designed, intended, authorized, or warranted for use as components in systems intended for surgical implant into
the body, or in other applications intended to support or sustain life, or where malfunction of IXYS Integrated Circuits Division’s product may result in direct physical
harm, injury, or death to a person or severe property or environmental damage. IXYS Integrated Circuits Division reserves the right to discontinue or make changes
to its products at any time without notice.
Specification: AN-151-R02
Copyright © 2014, IXYS Integrated Circuits Division
OptoMOS® is a registered trademark of IXYS Integrated Circuits Division
All rights reserved. Printed in USA.
4/14/2014
AN-151-R02
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