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參數(shù)資料
| 型號： | TCA3388FP |
| 廠商： | MOTOROLA INC |
| 元件分類： | 模擬傳輸電路 |
| 英文描述： | TELEPHONE LINE INTERFACE |
| 中文描述： | TELECOM-SLIC, PDSO20 |
| 封裝： | PLASTIC, SOIC-20 |
| 文件頁數(shù)： | 8/16頁 |
| 文件大?。?/td> | 274K |
| 代理商： | TCA3388FP |
TCA3388
8
MOTOROLA ANALOG IC DEVICE DATA
The TCA3388 offers the possibility to connect 2 sidetone
networks Z1 and Z2. For correct dc operation, the dc
impedance of these networks must be equal. When only 1
sidetone network is used, Pin HYS has to be connected to
HYL. All formulas below are based on a single sidetone
network, so only Z1 appears. When 2 sidetone networks are
used, Z1 has to be replaced by Z1//Z2.
In region 1, the transfer of the amplifier G at the HYL/HYS
inputs equals zero. The voltage difference between SAO and
SAI will equal VO1. The slope RE1 of the VLine, ILine
characteristic will equal:
RE1
R1 x
1
Z0
Z21
In region 2, the output current of the amplifier G will be
proportional to the input current. As a result the voltage
between SAO and SAI will increase with the line voltage.
Speech signals on the line are of no influence on this
because they are filtered out via capacitor C16. The slope
RE2 of the VLine, ILine characteristic will equal:
RE2
R1 x
1
1
RI
Z1
Z21
Z0
In region 3, the output current of the amplifier G is kept
constant. As a result the slope in region 3 will equal the slope
of region 1.
The transfer from region 2 to 3 occurs at the point VLK, ILK
defined by:
ILK
Z21
Z0
x Z1 x I2CD
2 VBE
VCD
R1
VLK = Z1 x I2CD + 2 VBE + VCD + VO2
With:
and 2 VBE
1.4 V, V02
1.1 V
I2CD
I2C
I2D
2
, and VCD
VC
VD
2
,
When the French or U.K. mask is selected, this transfer
takes places for line currents of 30 mA to 40 mA depending
on the components settings. With the Startup and Low
Voltage mask, the transfer lies outside the normal operating
range with line currents of 90 mA or more. In most
applications the transfer from region 1 to 2 takes place for line
currents below 10 mA.
With proper settings, region 4 is entered only during an
overload condition. In this mode, the power consumption in
the telephone set is limited. In order to detect an overload
condition, the voltage between the Pins LAI and SAO is
monitored. When the voltage difference is larger than the
threshold VClamp1, the protection is made active. The relation
for the line voltage VLP at this point is given as:
VLP
Z0
VCD
VO2
When the protection mode is entered, the line current is
reduced to a lower value ILP of:
ILP
VClamp2
(VO1 – VO2)
R1
When the line voltage becomes lower than VLP, the
overload condition is removed and the TCA3388 will leave
region 4.
The current drawn from the line by the dc part is used to
supply the TCA3388 and peripheral circuits. The excess loop
current is absorbed by the voltage regulator at Pin VCC,
where a filter capacitor is connected. The reference for the
circuit is Pin Gnd.
Startup of the application is ensured by an internal startup
circuit. When the line current flows, the hook status output
pin HSO goes high. This informs the microcontroller that the
set is off–hook. When the line current is no longer present the
pin will go low again. Because the line current is monitored,
and not the line voltage, also an interrupt of the exchange
can be recognized.
AC CHARACTERISTICS
Impedance
In Figure 6, the block diagram of the TCA3388 performing
the ac impedance is depicted. As can be seen it is partly
common with the dc mask block diagram. The part
generating the dc mask is replaced by a dc voltage source
because for ac, this part has no influence.
Line +
Line –
Figure 6. AC Stage of the TCA3388
T3
T2
Z0
R5
V02
C7
V
LAI
LAO
Gnd
R1
TCA3388
CC
Z21
SAO
SAI
VO1
When calculating the ac loop, it can be derived that the set
impedance Zin equals
Zin
VLine
ILine
R1
1
Z0
Z21
R1 xZ0
Z21
As can be noticed, the formula for the ac impedance Zin
equals the formula for the dc slope in regions 1 and 3.
However, because for the dc slope the resistive part of Z0
and Z21 are used, the actual values for Zin and the dc slopes
do not have to be equal.
A complex impedance can be made by making either Z0
or Z21 complex. When Z0 is made complex to fit the set
impedance the transmit characteristics will be complex as
well. The complex impedance is therefore preferably made
via the Z21 network. Because Z21 is in the denominator of
the Zin formula, Z21 will not be a direct copy of the required
impedance but a derivative of it. Figure 7 gives this derived
network to be used for Z21.
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