ADP5043ACPZ-1-R7 datasheet(21/30 Pages) AD

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Data Sheet

ADP5043

Rev. C | Page 21 of 30

APPLICATIONS INFORMATION

BUCK EXTERNAL COMPONENT SELECTION

Trade-offs between performance parameters such as efficiency

and transient response are made by varying the choice of

external components in the applications circuit, as shown in

Figure 48.

ADP5043

MICROPROCESSOR

VCC

VOUT1

VOUT2

nRSTO

WDI1

RESET

WDI2

VIN1

I/O

VCORE

VDDIO

Figure 48. Typical Applications Circuit

Inductor

The high switching frequency of the buck regulator of the

ADP5043 allows for the selection of small chip inductors. For

best performance, use inductor values between 0.7 μH and

3 μH. Suggested inductors are shown in Table 11.

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

the following equation:

OUT

RIPPLE









)

(

where:

fSW is the switching frequency.

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:

)

(

RIPPLE

MAX

LOAD

PEAK





Table 11. Suggested 1.0 μH Inductors

Vendor

Model

Dimensions

(mm)

ISAT

(mA)

DCR

(mΩ)

Murata

LQM2MPN1R0NG0B

2.0 × 1.6 × 0.9

1400

Murata

LQM18FN1R0M00B

1.6 × 0.8 × 0.8

150

Taiyo Yuden

CBMF1608T1R0M

1.6 × 0.8 × 0.8

290

Coilcraft

EPL2014-102ML

2.0 × 2.0 × 1.4

900

TDK

GLFR1608T1R0M-LR

1.6 × 0.8 × 0.8

230

Coilcraft

0603LS-102

1.8 × 1.69 × 1.1

400

Toko

MDT2520-CN

2.5 × 2.0 × 1.2

1350

Inductor conduction losses are caused by the flow of current

through the inductor, which has an associated internal dc

resistance (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 buck is a high switching frequency dc-to-dc converter,

shielded ferrite core material is recommended for its low core

losses and low EMI.

Output Capacitor

Higher output capacitor values reduce the output voltage

ripple and improve load transient response. When choosing

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

of capacitance due to output voltage dc bias.

Ceramic capacitors are manufactured with a variety of dielec-

trics, each with a different behavior over temperature and

applied voltage. Capacitors must have a dielectric adequate to

ensure the minimum capacitance over the necessary temper-

ature range and dc bias conditions. X5R or X7R dielectrics with

a voltage rating of 6.3 V or 10 V are highly recommended for

best performance. Y5V and Z5U dielectrics are not recommended

for use with any dc-to-dc converter because of their poor

temperature and dc bias characteristics.

The worst-case capacitance accounting for capacitor variation

over temperature, component tolerance, and voltage is calcu-

lated using the following equation:

CEFF = COUT × (1 − TEMPCO) × (1 − TOL)

where:

CEFF is the effective capacitance at the operating voltage.

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 COUT is 9.2481 μF at 1.8 V, as shown in Figure 49.

Substituting these values in the equation yields

CEFF = 9.2481 μF × (1 − 0.15) × (1 − 0.1) = 7.0747 μF

To guarantee the performance of the buck regulator, it is

imperative that the effects of dc bias, temperature, and

tolerances on the behavior of the capacitors be evaluated

for each application.

0123

456

DC BIAS VOLTAGE (V)

Figure 49. Typical Capacitor Performance

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