LT6301CFE Linear Technology, LT6301CFE Datasheet - Page 13

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

Specifications of LT6301CFE

• 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: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
of n. To analyze this circuit, first ground the input. As R
R
Eliminating V
For example, reducing R
amplifer gain of (1 + R
= 12.3.
Note that the overall gain is increased:
A simpler method of using positive feedback to reduce the
back-termination is shown in Figure 14. In this case, the
drivers are driven differentially and provide complemen-
tary outputs. Grounding the inputs, we see there is invert-
ing gain of –R
L
/n, and assuming R
V
R
V
V
(1 + R
V
V
V
A
P
O
A
BT
O
I
Figure 13. Back Termination Using Postive Feedback
= V
= V
= V
= V
by n.
V
P2
I
O
O
P
O
1 1
/R
(1 – 1/n)/(1 + R
(1 + R
(R
(1 – 1/n) to increase the effective value of
R
P
P1
P1
F
F
R
, we get the following:
/R
/R
G
/ /
) = (1 + R
n
V
P
P
P2
P
)
from –V
U
/R
+
–
1
P1
R
P2
FOR R
V
V
1 +
O
F
I
P
)
BT
R R
>>R
/R
R
=
2
F
U
F
R
F
R
/R
BT
by a factor of n = 4, and with an
G
/
G
F
F
/
O
R
1 +
/R
) = 10 requires that R
1 + 1/n
=
G
L
R
R
P2
to V
G
R
P1
R
)/(1 – 1/n)
n
G
we require that:
P
R
L
P2
R
R
)
+ R
G
2
P1
F
/(R
V
A
P2
P2
–
A
W
R
R
R
+ R
= 1 –
P2
R
P
R
P
BT
1
P1
+ R
P1
1
)
/
1
n
R
P1
R
L
V
P
O
2
6301
F13
U
R
P
1
P2
/R
BT
P1
=
and assuming R
solving
So to reduce the back-termination by a factor of 3 choose
R
Using positive feedback is often referred to as active
termination.
Figure 16 shows a full-rate ADSL line driver incorporating
positive feedback to reduce the power lost in the back
termination resistors by 40% yet still maintains the proper
impedance match to the100 characteristic line imped-
ance. This circuit also reduces the transformer turns ratio
over the standard line driving approach resulting in lower
peak current requirements. With lower current and less
power loss in the back termination resistors, this driver
dissipates only 1W of power, a 30% reduction.
While the power savings of positive feedback are attractive
there is one important system consideration to be ad-
dressed, received signal sensitivity. The signal received
Figure 14. Back Termination Using Differential Postive Feedback
F
/R
V
R
V
–V
A
O
F
P
V
/R
/V
I
I
= V
= 2/3. Note that the overall gain is increased to:
P
I
R
R
= (1 + R
G
G
O
= 1 – 1/n
+
–
–
+
(1 – 1/n)
R
R
P
P
P
F
/R
>> R
R
R
F
F
G
–V
V
+ R
A
A
L
, we require
R
R
BT
BT
F
/R
P
)/[2(1 – R
6301
F14
R
R
L
L
V
–V
O
O
F
/R
FOR R
n =
V
V
O
P
I
LT6301
=
)]
1 –
BT
1 +
2
1
R
R
=
1 –
F
P
sn6301 6301f
R
R
13
R
G
F
n
L
+
R
R
P
F
R
R
P
F