TA0313 Datasheet, PDF (3/9 Pages) STMicroelectronics – STMicroelectronics Solutions for ADSL Line Interfaces

STMicroelectronics Solutions for ADSL Line Interfaces
TA0313
Figure 3: Thermal considerations: power dissipation of the drivers vs. room temperature
5
TS612ID, Rthja=45°C/W
4
3
TS613IPW, Rthja=70°C/W
2
TS613ID, Rthja=175°C/W
1
0
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80
Room Temperature (°C)
The TS612 comes in SO20 plastic batwing package which increases its power dissipation capability to
2.7W at room temperature. It features a power-down or stand-by function in order to minimize the
consumption when the modem is not in communication.
Power Supply
Remote ADSL modem terminals must be designed to be easily connected to a PC. For such applications,
the driver should use a +12V single power supply, which is available via standard PCI connectors. Note
that the TS613 and TS612 can also be powered by a dual power supply at +/-6V.
Figure 4 shows a single +12V supply circuit with the TS613 as a remote terminal transmitter in differential
mode. Note that one could also use the TS612 in exactly the same schema.
Figure 4: Implementation of the TS613 as a differential line driver with a +12V single supply
100n
+12V
1k
Vi
3k9
3 ₊ ⁸ _+12V
2^_
1
R2
12.5Ω
½ R1
½ R1
Vi
10µ _3k9 100n
1k _GND
100n
6 ^{_ R4}
7
5+
GND
4
12.5Ω
1µ
10n
Vo
25Ω
Vo
1:2
Hybrid
&
100Ω
Transformer
The driver is biased with a mid-supply (nominally +6V) in order to maintain the DC component of the
signal at +6V. This allows a maximum dynamic range between 0 and +12 V. Several options are possible
in order to provide this bias supply—such as for example, a virtual ground using an operational amplifier,
or, the cheapest solution, a two-resistor divider. A high resistance value is required to limit the current
consumption. On the other hand, the current must be high enough to bias the inverting input of the driver.
If we consider the positive input’s bias current (15µA max) as 1% of the current through the resistance
divider (1.5mA), two 3.9kΩ resistors are sufficient to keep a stable mid-supply .
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