ADP2386

Data Sheet

Rev. A | Page 16 of 24

For a duty cycle that is larger than 50%, the minimum inductor

value is determined using the following equation:

L (Minimum) =

SW

OUT

f

D

V

×

−

×

2

)

1

(

The peak inductor current is calculated by

2

L

I

∆

The saturation current of the inductor must be larger than the peak

inductor current. For ferrite core inductors with a quick saturation

characteristic, the saturation current rating of the inductor must

be higher than the current-limit threshold of the switch. This

prevents the inductor from reaching saturation.

The rms current of the inductor is calculated as follows:

12

2

2

L

OUT

I

I

∆

+

Shielded ferrite core materials are recommended for low core

loss and low EMI. Table 7 lists some recommended inductors.

OUTPUT CAPACITOR SELECTION

The output capacitor selection affects the output ripple voltage

load step transient and the loop stability of the regulator.

For example, during a load step transient where the load is

suddenly increased, the output capacitor supplies the load until

the control loop can ramp up the inductor current. The delay

caused by the control loop causes output undershoot. The

output capacitance that is required to satisfy the voltage droop

requirement can be calculated using the following equation:

UV

OUT

OUT

IN

STEP

UV

V

V

V

L

I

K

_

2

)

(

2

∆

×

−

×

×

∆

×

where:

Another example occurs when a load is suddenly removed from

the output, and the energy stored in the inductor rushes into

the output capacitor, causing the output to overshoot.

The output capacitance that is required to meet the overshoot

requirement can be calculated using the following equation:

2

2

_

2

)

(

OUT

OV

OUT

OUT

STEP

OV

V

V

V

L

I

K

−

∆

+

×

∆

×

where:

The output ripple is determined by the ESR and the value of the

capacitance. Use the following equations to select a capacitor

that can meet the output ripple requirements:

RIPPLE

OUT

SW

L

V

f

I

_

8

∆

×

×

∆

L

RIPPLE

OUT

I

V

∆

∆

_

where:

in ohms (Ω).

performance.

Table 7. Recommended Inductors

Vendor

Part No.

Value (µH)

DCR (mΩ)

Toko

FDVE0630-R47M

0.47

15.6

14.1

3.7

FDVE0630-R75M

0.75

10.9

10.7

6.2

FDVE0630-1R0M

1.0

9.5

9.5

8.5

FDVE1040-1R5M

1.5

13.7

14.6

4.6

FDVE1040-2R2M

2.2

11.4

11.6

6.8

FDVE1040-3R3M

3.3

9.8

9.0

10.1

FDVE1040-4R7M

4.7

8.2

8.0

13.8

Vishay

IHLP3232DZ-R47M-11

0.47

14

25

2.38

IHLP3232DZ-R68M-11

0.68

14.5

22.2

3.22

IHLP3232DZ-1R0M-11

1.0

12

18.2

4.63

IHLP4040DZ-1R5M-01

1.5

27.5

15

5.8

IHLP4040DZ-2R2M-01

2.2

25.6

12

9

IHLP4040DZ-3R3M-01

3.3

18.6

10

14.4

IHLP4040DZ-4R7M-01

4.7

17

9.5

16.5

Wurth Elektronik

744 325 120

1.2

25

20

1.8

744 325 180

1.8

18

16

3.5

744 325 240

2.4

17

14

4.75

744 325 330

3.3

15

12

5.9

744 325 420

4.2

14

11

7.1