current will ramp up to a high level before the current-lim-

it comparator can turn off the switch. The minimum on-time

The standard operating circuits use a 22µH inductor.

If a different inductance value is desired, select L such

that:

L

≥ —————----—--

Larger inductance values tend to increase the start-up

time slightly, while smaller inductance values allow the

coil current to ramp up to higher levels before the

switch turns off, increasing the ripple at light loads.

Inductors with a ferrite core or equivalent are recom-

mended; powder iron cores are not recommended for

use with high switching frequencies. Make sure the

inductor’s saturation current rating (the current at which

the core begins to saturate and the inductance starts to

However, it is generally acceptable to bias the inductor

into saturation by approximately 20% (the point where

the inductance is 20% below the nominal value). For

highest efficiency, use a coil with low DC resistance,

preferably under 20m

Ω. To minimize radiated noise,

use a toroid, a pot core, or a shielded coil.

Table 1 lists inductor suppliers and specific recom-

mended inductors.

5V or Adjustable, Low-Voltage,

Step-Up DC-DC Controller

_______________________________________________________________________________________

9

0

INPUT VOLTAGE (V)

0.5

1.0

1.5

2.0

2.5

3.0

3.5

23

4

5

L = 22

µH

0

INPUT VOLTAGE (V)

0.5

1.0

1.5

2.0

2.5

3.0

3.5

2

4

6

8

10

12

L = 22

µH

Figure 4b. Maximum Output Current vs. Input Voltage

Figure 4c. Maximum Output Current vs. Input Voltage

Figure 4d. Maximum Output Current vs. Input Voltage

Figure 4a. Maximum Output Current vs. Input Voltage

0

INPUT VOLTAGE (V)

0.5

1.0

1.5

2.0

2.5

3.0

3.5

2

4

6

8

10

12

14

16

L = 22

µH

0

2.0

INPUT VOLTAGE (V)

2.0

2.5

3.0

3.5

0.5

1.0

1.5

L = 22

µH