LT6301CFE#PBF Linear Technology, LT6301CFE#PBF Datasheet - Page 14

• Manufacturer Part Number: LT6301CFE#PBF
• Description: IC XDSL LINE DRIVER DUAL 28TSSOP
• Manufacturer: Linear Technology
• Type: Driverr

Specifications of LT6301CFE#PBF

• Number Of Drivers/receivers: 2/0
• Protocol: xDSL
• Voltage - Supply: 5 V ~ 12 V
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP Exposed Pad, 28-eTSSOP, 28-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
LT6301
from the line is sensed across the back termination resis-
tors. With positive feedback, signals are present on both
ends of the R
Extra gain may be required in the receive channel to
compensate, or a completely separate receive path may be
implemented through a separate line coupling transformer.
Considerations for Fault Protection
The basic line driver design, shown on the front page of
this data sheet, presents a direct DC path between the
outputs of the two amplifiers. An imbalance in the DC
biasing potentials at the noninverting inputs through
either a fault condition or during turn-on of the system can
create a DC voltage differential between the two amplifier
outputs. This condition can force a considerable amount
of current to flow as it is limited only by the small valued
back-termination resistors and the DC resistance of the
transformer primary. This high current can possibly cause
the power supply voltage source to drop significantly
impacting overall system performance. If left unchecked,
the high DC current can heat the LT6301 to thermal
shutdown.
14
BT
resistors, reducing the sensed amplitude.
U
U
1000pF
Figure 15. Protecting the Driver Against Load Faults and Line Transients
+IN
–IN
W
110
110
+
–
–
+
LT6301
LT6301
U
1/4
1/4
1k
1k
–12V
12V
SHDN
SHDNREF
24.9k
12.7
12.7
Using DC blocking capacitors, as shown in Figure 15, 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
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 LT6301 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
0.1 F
0.1 F
12V –12V
12V –12V
1:2
6301 F15
BAV99
BAV99
LINE
LOAD
sn6301 6301f
®
,