LT1794CFE Linear Technology, LT1794CFE Datasheet - Page 9

IC AMP XDSL LINE DRIVER 20TSSOP

LT1794CFE

Manufacturer Part Number
LT1794CFE
Description
IC AMP XDSL LINE DRIVER 20TSSOP
Manufacturer
Linear Technology
Type
Line Driver, Transmitterr
Datasheet

Specifications of LT1794CFE

Number Of Drivers/receivers
2/0
Protocol
xDSL
Voltage - Supply
18V
Mounting Type
Surface Mount
Package / Case
20-TSSOP Exposed Pad, 20-eTSSOP, 20-HTSSOP
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LT1794CFE
Manufacturer:
LT
Quantity:
5 988
APPLICATIO S I FOR ATIO
Logic Controlled Operating Current
The DSP controller in a typical xDSL application can have
I/O pins assigned to provide logic control of the LT1794
line driver operating current. As shown in Figure 4 one or
two logic control inputs can control two or four different
operating modes. The logic inputs add or subtract current
to the SHDN input to set the operating current. The one
logic input example selects the supply current to be either
full power, 10mA per amplifier or just 2mA per amplifier,
which significantly reduces the driver power consumption
while maintaining less than 2
frequencies less than 1MHz. This low power mode retains
termination impedance at the amplifier outputs and the
line driving back termination resistors. With this termina-
tion, while a DSL port is not transmitting data, it can still
sense a received signal from the line across the back-
termination resistors and respond accordingly.
The two logic input control provides two intermediate
(approximately 7mA per amplifier and 5mA per amplifier)
operating levels between full power and termination modes.
These modes can be useful for overall system power
management when full power transmissions are not
necessary.
U
U
Figure 4. Providing Logic Input Control of Operating Current
W
output impedance to
Two Control Inputs
One Control Input
V
H
H
C1
L
L
V
R
V
R
LOGIC
R
LOGIC
SHDN
R
V
SHDN
R
V
H
H
H
CO
C0
L
L
L
C1
U
C
C
RESISTOR VALUES (k )
R
RESISTOR VALUES (k )
R
SUPPLY CURRENT PER AMPLIFIER (mA)
SUPPLY CURRENT PER AMPLIFIER (mA)
40.2
11.5
19.1
40.2
7.32
SHDN
3V
SHDN
3V
10
10
7
5
2
2
TO V
TO V
3.3V
43.2
13.0
22.1
3.3V
43.2
8.25
10
10
7
5
2
2
CC
CC
(12V)
(12V)
60.4
21.5
36.5
60.4
13.7
5V
5V
10
10
7
5
2
2
Shutdown and Recovery
The ultimate power saving action on a completely idle port
is to fully shut down the line driver by pulling the SHDN pin
to within 0.4V of the SHDNREF potential. As shown in
Figure 5 complete shutdown occurs in less than 10 s and,
more importantly, complete recovery from the shut down
state to full operation occurs in less than 2 s. The biasing
circuitry in the LT1794 reacts very quickly to bring the
amplifiers back to normal operation.
SHDNREF = 0V
4.99
8.66
14.3
4.99
5.49
AMPLIFIER
R
R
3V
3V
10
10
7
5
2
2
SHDN
SHDN
OUTPUT
V
SHDN
3.3V
6.81
10.7
17.8
3.3V
6.81
6.65
TO V
TO V
10
10
7
5
2
2
Figure 5. Shutdown and Recovery Timing
LOGIC
LOGIC
19.6
20.5
34.0
19.6
12.7
1794 F04
5V
5V
10
10
7
5
2
2
0V
0V
V
V
LOGIC
LOGIC
V
V
V
C1
C0
C
R
R
R
C1
C0
C
12V OR V
12V OR V
R
2k
R
2k
LOGIC
LOGIC
SHDN
SHDNREF
SHDN
SHDNREF
SHDN
SHDN
1794 F05
LT1794
9

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