ADP2147

Rev. 0 | Page 13 of 16

APPLICATIONS INFORMATION

EXTERNAL COMPONENT SELECTION

Trade-offs between performance parameters such as efficiency

and transient response can be made by varying the choice of

external components in the applications circuit, as shown in

Figure 1.

Inductor

The high switching frequency of the ADP2147 allows for the

selection of small chip inductors. For best performance, use

inductor values between 0.7 μH and 3 μH. Recommended

inductors are shown in Table 6.

The peak-to-peak inductor current ripple is calculated using

the following equation:

L

f

V

V

V

V

I

SW

IN

OUT

IN

OUT

RIPPLE

×

×

−

×

=

)

(

where:

L is the inductor value.

The minimum dc current rating of the inductor must be greater

than the inductor peak current. The inductor peak current is

calculated using the following equation:

2

)

(

RIPPLE

MAX

LOAD

PEAK

I

I

I

+

=

Inductor conduction losses are caused by the flow of current

through the inductor, which has an associated internal DCR.

Larger sized inductors have smaller DCR, which may decrease

inductor conduction losses. Inductor core losses are related to

the magnetic permeability of the core material. Because the

ADP2147 is a high switching frequency dc-to-dc regulator,

shielded ferrite core material is recommended for its low core

losses and low electromagnetic interference (EMI). Table 6

shows the suggested inductors that can be used for different

output current requirements; several inductors are also listed to

minimize PCB space for small current applications.

Table 6. Suggested 1.0 μH Inductors

Vendor

Model

Dimensions

(mm)

(mA)

DCR

(mΩ)

Murata

LQM2MPN1R0NG0B

2.0 × 1.6 × 0.9

1400

85

LQM18PN1R0

1.6 × 0.8 × 0.33

700

52

Coilcraft®

EPL2014-102ML

2.0 × 2.0 × 1.4

900

59

0603LS-102

1.8 × 1.27 × 1.1

400

81

Toko

MDT2520-CN

2.5 × 2.0 × 1.2

1800

100

TDK

GLFR1608T1R0M-LR

1.6 × 0.8 × 0.8

360

80

Taiyo Yuden

CBMF1608T1R0M

1.6 × 0.8 × 0.8

290

90

Output Capacitor

Increasing the value of the output capacitor reduces the output

voltage ripple and improves load transient response. When

choosing the capacitor value, it is also important to account for

the loss of capacitance due to dc output voltage bias.

Ceramic capacitors are manufactured with a variety of dielectrics,

each with different behavior over temperature and applied voltage.

Capacitors must have a dielectric adequate to ensure the

minimum capacitance over the necessary temperature range

and dc bias conditions. X5R or X7R dielectrics with a voltage

rating of 6.3 V or 10 V are recommended for best performance.

Y5V and Z5U dielectrics are not recommended for use with any

dc-to-dc regulator because of their poor temperature and dc bias

characteristics.

The worst-case capacitance, accounting for capacitor variation

over temperature, component tolerance, and voltage, is

calculated using the following equation:

where:

TEMPCO is the worst-case capacitor temperature coefficient.

TOL is the worst-case component tolerance.

In this example, the worst-case temperature coefficient (TEMPCO)

over −40°C to +85°C is assumed to be 15% for an X5R dielectric.

The tolerance of the capacitor (TOL) is assumed to be 10%, and

Substituting these values in the equation yields

To guarantee the performance of the ADP2147, it is imperative

that the effects of dc bias, temperature, and tolerances on the

behavior of the capacitors be evaluated for each application.

6

5

4

3

2

1

0

01

2

3

4

5

6

DC BIAS VOLTAGE (V)

Figure 34. Typical Capacitor Performance

The peak-to-peak output voltage ripple for the selected output

capacitor and inductor values is calculated using the following

equation:

()

OUT

SW

IN

RIPPLE

C

L

f

V

V

×

×

×

×

=

2

2π

OUT

SW

RIPPLE

C

f

I

×

×

=

8