8

LT6300

Logic Controlled Operating Current

The DSP controller in a typical xDSL application can have

I/O pins assigned to provide logic control of the LT6300

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

APPLICATIO S I FOR ATIO

4

7

10

50

90

130

170

210

250

30

70

100

150

190

230

270 290

20

25

30

35

40

6300 F03

5

10

15

0

45

SHDN

SHDNREF

• 64 – 5k

• 64

≈

while maintaining less than 2

Ω output impedance to

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

Two Control Inputs

RESISTOR VALUES (k

Ω)

3V

40.2

11.5

19.1

3.3V

43.2

13.0

22.1

5V

60.4

21.5

36.5

3V

4.99

8.66

14.3

3.3V

6.81

10.7

17.8

5V

19.6

20.5

34.0

H

L

H

L

H

H

L

L

10

7

5

2

10

7

5

2

10

7

5

2

10

7

5

2

10

7

5

2

10

7

5

2

SUPPLY CURRENT PER AMPLIFIER (mA)

One Control Input

RESISTOR VALUES (k

Ω)

3V

40.2

7.32

3.3V

43.2

8.25

5V

60.4

13.7

3V

4.99

5.49

3.3V

6.81

6.65

5V

19.6

12.7

H

L

10

2

10

2

10

2

10

2

10

2

10

2

SUPPLY CURRENT PER AMPLIFIER (mA)

0V

SHDN

SHDNREF

2k

0V

SHDN

SHDNREF

2k

Figure 4. Providing Logic Input Control of Operating Current