ADP2119/ADP2120

Rev. 0 | Page 18 of 24

APPLICATIONS INFORMATION

This section describes the selection of the external components

for the ADP2119/ADP2120. The typical application circuit for

the ADP2119 is shown in Figure 50.

10

EN

ADP2119

1

VIN

9

SYNC/MODE

2

PVIN

8

PGOOD

3

SW

7

TRK

4

PGND

6

FB

5

GND

R2

10k

Ω

5V

22µF

X5R

6.3V

22µF

X5R

6.3V

C1

0.1µF

R1

10

Ω

15k

Ω

2.5V

2A

L

1.5µH

47.5k

Ω

Figure 50. Typical Application Circuit

OUTPUT VOLTAGE SELECTION

The output voltage of the adjustable version can be set by an

external resistive voltage divider, and the following equation

calculates the output voltage.

)

(1

0.6

BOT

TOP

OUT

R

R

V

+

×

=

To limit the output voltage accuracy degradation due to FB bias

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

INDUCTOR SELECTION

The inductor value is determined by the operating frequency,

input voltage, output voltage, and ripple current. A small inductor

value leads to a larger inductor current ripple and provides a

faster transient response; however, it degrades efficiency. A

large inductor value leads to a smaller current ripple and good

efficiency but slows the transient response. As a guideline, the

load current trade-off between the transient response and efficiency.

The inductor value can be calculated using the following equation:

(

)

S

L

OUT

IN

f

I

D

V

V

L

×

×

−

=

Δ

where:

Δ

The regulator uses slope compensation in the current loop to

prevent subharmonic oscillations when the duty cycle is larger

than 50%. The internal slope compensation limits the minimum

inductor value.

The negative current limit (−0.6 A) also limits the minimum

by the selected inductor should not exceed 1.2 A.

The peak inductor current should be kept below the peak current

limit threshold value and can be calculated from

2

L

O

PEAK

I

I

I

Δ

+

=

Ensure that the rms current of the selected inductor is greater

than the maximum load current and that its saturation current

is greater than the peak current limit of the regulator.

OUTPUT CAPACITOR SELECTION

The output voltage ripple, load step transient, and loop stability

determine the output capacitor selection.

The ESR and the capacitance determine the output ripple.

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

×

×

+

×

Δ

=

Δ

S

OUT

L

OUT

f

C

ESR

I

V

8

1

The load transient response depends on the inductor, the output

capacitor, and the control loop.

The ADP2119/ADP2120 have integrated loop compensation to

provide a simple power solution design. Table 5 and Table 6 show

the typical recommended inductors and capacitors for the ADP2119/

ADP2120. X5R or X7R ceramic capacitors are highly recommended.

L (μH)

3.3

1.0

1

22 + 22

3.3

1.2

1

22 + 22

3.3

1.5

1

22 + 10

3.3

1.8

1

22

3.3

2.5

1

22

5

1.0

1

22 + 22

5

1.2

1.5

22 + 22

5

1.5

1.5

22 +10

5

1.8

1.5

22 +10

5

2.5

1.5

22

5

3.3

1.5

22

L (μH)

3.3

1.0

1.5

22 + 10

3.3

1.2

1.5

22 + 10

3.3

1.5

1.5

22 + 10

3.3

1.8

1.5

10 + 10

3.3

2.5

1.5

10 + 10

5

1.0

1.5

22 + 10

5

1.2

1.5

22 + 10

5

1.5

2.2

22 + 10

5

1.8

2.2

10 + 10

5

2.5

2.2

10 + 10

5

3.3

2.2

10 + 10