lt1739 Linear Technology Corporation, lt1739 Datasheet - Page 15

• Manufacturer Part Number: lt1739
• Description: Dual 500ma, 200mhz Xdsl Line Driver Amplifier
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Using DC blocking capacitors, as shown in Figure 16, to
AC couple the signal to the transformer eliminates the
possibility for DC current to flow under any conditions.
These capacitors should be sized large enough to not
impair the frequency response characteristics required for
the data transmission.
Another important fault related concern has to do with
very fast high voltage transients appearing on the tele-
phone line (lightning strikes for example). TransZorbs
varistors and other transient protection devices are often
used to absorb the transient energy, but in doing so also
U
U
Figure 16. Protecting the Driver Against Load Faults and Line Transients
1000pF
W
+IN
–IN
110
110
U
+
–
–
+
LT1739
LT1739
1/2
1/2
1k
1k
–12V
12V
®
,
SHDN
SHDNREF
24.9k
create fast voltage transitions themselves that can be
coupled through the transformer to the outputs of the line
driver. Several hundred volt transient signals can appear
at the primary windings of the transformer with current
into the driver outputs limited only by the back termination
resistors. While the LT1739 has clamps to the supply rails
at the output pins, they may not be large enough to handle
the significant transient energy. External clamping diodes,
such as BAV99s, at each end of the transformer primary
help to shunt this destructive transient energy away from
the amplifier outputs.
TransZorb is a registered trademark of General Instruments, GSI
12.7
12.7
0.1 F
0.1 F
12V –12V
12V –12V
1:2
1739 F16
BAV99
BAV99
LINE
LOAD
LT1739
1739fas, sn1739
15