ADP2389/ADP2390

Data Sheet

APPLICATIONS INFORMATION

INPUT CAPACITOR SELECTION

The input decoupling capacitor attenuates high frequency noise

on the input. This capacitor must be a ceramic type in the range

of 10 µF to 47 µF. Place the capacitor close to the PVIN pin. Keep

the loop composed by this input capacitor, high-side MOSFET

and low-side MOSFET as small as possible.

The voltage rating of the input capacitor must be greater than

the maximum input voltage. The rms current rating of the input

capacitor must be larger than the value calculated from the

following equation:

(

)

D

D

I

I

OUT

RMS

CIN

–

1

_

×

×

=

where:

D is the duty cycle.

OUTPUT VOLTAGE SETTING

An external resistor divider sets the output voltages of the

ADP2389/ADP2390. Calculate the resistor values using the

following equation:













+

×

=

BOT

TOP

OUT

R

R

V

1

6

.

0

where :

To limit output voltage accuracy degradation due to FB bias

current (0.1 µA maximum) to less than 0.5% (maximum),

Table 5 gives the recommended resistor divider for various

output voltages.

Table 5. Resistor Divider for Difference Output Voltage

1.0

10

15

1.2

10

10

1.5

15

10

1.8

20

10

2.5

47.5

15

3.3

10

2.21

5.0

22

3

INDUCTOR SELECTION

The inductor value is determined by the operating frequency,

the input voltage, output voltage, and inductor ripple current.

Using a small inductor leads to a faster transient response; however,

it degrades efficiency due to its larger inductor ripple current.

Using a large inductor value leads to smaller ripple current and

better efficiency but results in a slower transient response.

to one third of the maximum load current. Calculate the inductor

value using the following equation:

SW

L

OUT

IN

f

I

D

V

V

L

×

∆

×

=

)

–

(

where:

D is the duty cycle.

IN

OUT

V

V

D =

2

L

OUT

PEAK

I

I

I

∆

+

=

The saturation current of the inductor must be greater than the

peak inductor current. For the ferrite core inductors with a quick

inductor must be greater than the current-limit threshold of the

switch to prevent the inductor from being saturated.

following equation:

12

2

2

L

OUT

RMS

I

I

I

∆

+

=

Shielded ferrite core materials are recommended for low core

loss and low electromagnetic interference (EMI). Table 6 lists

recommended inductors.

Table 6. Recommended Inductors

Vendor

Device No.

Value

(µH)

(A)

(A)

DCR

(mΩ)

CoilCraft

XAL7030-102ME

1

21.8

16.1

4.55

XAL7030-152ME

1.5

11.9

23.5

7.6

XAL7030-222ME

2.2

10

18

13.7

Toko

FDUE1040D-H-R22M

0.22

32

32

0.64

FDUE1040D-H-R45M

0.45

27

24

1.02

FDU1040D-H-R68M

0.68

21

20

1.7

FDUE1040D-H-1R0M

1.0

18

16

2.35

FDA1254-H-1R2M

1.2

20.2

18.4

2.6

Würth

Elektronik

744 333 0022

0.22

60

21.5

0.6

744 333 0047

0.47

47

20

0.8

744 333 0068

0.68

38

20

1.35

744 333 0082

0.82

36

20

1.35

744 332 0100

1.0

27.5

20

1.35

744 325 120

1.2

25

20

1.8

744 333 0150

1.5

27

18

2.5

744 333 0220

2.2

22

16

3.7

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