ADP2503/ADP2504

Preliminary Technical Data

APPLICATIONS INFORMATION

INDUCTOR SELECTION

The high 2.5 MHz switching frequency of the ADP2503/

ADP2504 allows for minimal output voltage ripple, while

minimizing inductor size and cost. Careful inductor selection

also optimizes efficiency and reduces electromagnetic interfe­

rence (EMI). The selection of the inductor value determines the

inductor current ripple and loop dynamics.

V

ΔI , peak (Buck) =

L

V

× f

× L

IN

OSC

(V

V

ΔI

×

IN

V

f

× L

OUT

OSC

and L is the inductor value in henries.

A larger inductor value reduces the current ripple (and

therefore peak inductor current), but is physically larger in size

with increased dc resistance. Inductor values between 1 μH and

1.5 μH are usually suggested. The maximum inductor value to

ensure stability is 2.0 μH. For increased efficiency with the

ADP2504, it is suggested a 1.5 μH inductor be used.

The inductor peak current is at the maximum in boost mode.

To determine the actual maximum inductor current in boost

mode, the input dc current should be estimated.

⎛ V

1

I

⎜⎜

⎟⎟×

V

IN

⎠ η

⎝

where η is efficiency (assume η ≈ 0.85 to 0.90).

The saturation current rating of the inductor must be at least

Ceramic multilayer inductors can be used with lower current

designs for a reduced overall solution size and dc resistance (DCR).

These are available in low profile packages. Care must be taken as

these derate quickly as the inductor value is increased especially at

higher operating temperatures.

Ferrite core inductors have good core loss characteristics as well as

reasonable dc resistance. A shielded ferrite inductor reduces the

EMI generated by the inductor.

Table 5. Recommended Output Capacitors

Table 4. Sample of Recommended Inductors

Vendor

Value

(μH)

Part No.

DCR

(mΩ)

(A)

Dimensions

L × W × H

(mm)

Toko

Toko

Toko

Murata

Murata

TDK

TDK

Coilcraft

Coilcraft

1.2

1.5

1

1

1.5

1.0

1.5

1.0

1.5

DE2810C

DE2810C

MDT2520-CN

LQM2HP-G0

LQM2HP-G0

CPL2512T

CPL2512T

LPS3010

LPS3010

55

60

100

55

70

90

120

85

120

1.7

1.5

1.8

1.6

1.5

1.5

1.2

1.7

1.3

2.8 × 2.8 × 1.0

2.8 × 2.8 × 1.0

2.5 × 2 × 1.2

2.5 × 2 × 1

2.5 × 2 × 1

2.5 × 1.5 × 1.2

2.5 × 1.5 × 1.2

3.0 × 3.0 × 0.9

3.0 × 3.0 × 0.9

Output Capacitor Selection

The output capacitor selection determines the output voltage

ripple, transient response and the loop dynamics of the

ADP2503/ADP2504. The output voltage ripple for a given

output capacitor is given by

V

× (V − V

)

OUT

IN

OUT

ΔV

, peak (Buck) =

OUT

2

V

× 8 × L ×

IN

OSC

OUT

I

ΔV

×V

× f

OUT

OUT

OSC

If the ADP2503/ADP2504 are operating in buck mode, the

worst-case voltage ripple occurs for the highest input voltage,

The maximum voltage overshoot, or undershoot is inversely

proportional to the value of the output capacitor. To ensure

stability and excellent transient response, it is recommended to

use a minimum of 22 μF X5R 6.3 V or 2 × 10 μF X5R 6.3 V

capacitors at the output. The effective capacitance (includes

temperature, dc bias effects) needed for stability is 14 μF.

Vendor

Value

Part No.

Dimensions

L × W × H (mm)

Murata

2 × 10 μF, 6.3 V

GRM188R60J106ME47

1.6 × 0.8 × 0.8 (2)

TDK

2 × 10 μF, 6.3 V

C1608JB0J106K

1.6 × 0.8 × 0.8 (2)

Murata

22 μF, 6.3 V

GRM21BR60J226ME39

2 × 1.25 × 1.25

TDK

22 μF, 6.3 V

C2012X5R0J226M

2 × 1.25 × 1.25

TDK

22 μF, 10 V

C3216X5R1A226K

2 × 1.25 × 1.25

Murata

10 μF, 10 V

GRM21BR71A106KE51L

2 × 1.25 × 1.25 (2)

Rev. PrB | Page 12 of 16