Figure 9b. Maximum Output Current vs. Input Voltage,

Figure 9c. Maximum Output Current vs. Input Voltage,

Figure 9d. Maximum Output Current vs. Input Voltage,

Figure 9e. Maximum Output Current vs. Input Voltage,

Choosing an Inductor

Practical inductor values range from 22µH to 100µH,

and 47µH is normally a good choice. Inductors with a

ferrite core or equivalent are recommended. The induc-

tor’s saturation current rating – the current at which the

core begins to saturate and the inductance falls to 80%

or 90% of its nominal value – should ideally equal the

current limit (see

Current-Sense Resistor section).

However, because the current is limited by the

MAX749, the inductor can safely be driven into satura-

tion with only a slight impact on efficiency.

For highest efficiency, use a coil with low resistance,

preferably under 300m

Ω. To minimize radiated noise,

use a toroid, pot-core, or shielded inductor.

Digitally Adjustable LCD Bias Supply

_______________________________________________________________________________________

9

Figure 9a. Maximum Output Current vs. Input Voltage,

0

INPUT VOLTAGE (V)

5

10

15

20

25

3

24

5

6

1.0

0.5

0.3

0.25

0.2

L = 47

µH

80

0

26

20

60

INPUT VOLTAGE (V)

4

40

100

120

140

35

L = 47

µH

0.2

0.25

0.3

0.5

1.0

60

0

INPUT VOLTAGE (V)

6

20

24

40

80

100

35

L = 47

µH

0.2

0.25

0.3

0.5

1.0

60

0

10

50

INPUT VOLTAGE (V)

6

30

20

24

40

35

1.0

0.5

0.3

0.25

0.2

L = 47

µH

0

INPUT VOLTAGE (V)

50

100

150

200

250

3

24

5

6

1.0

0.5

0.3

0.25

0.2

L = 47

µH