ADP5350ACBZ-1-R7 datasheet(58/63 Pages) AD

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ADP5350

Data Sheet

Rev. B | Page 58 of 63

APPLICATIONS INFORMATION

EXTERNAL COMPONENTS

Buck Inductor Selection

The high switching frequency of the ADP5350 buck converter

allows the selection of small chip inductors. Suggested buck

inductors are shown in Table 81.

The peak-to-peak inductor current ripple, IRIPPLE, is calculated

using the following equation:

(

)

ISOS

CFL1

ISOS

RIPPLE

−

where:

VISOS is the ISOS node output voltage.

VCFL1 is the converter input voltage at the CFL1 node.

fSW is the switching frequency.

L1 is the buck output inductor value.

The minimum dc current rating of the inductor must be greater

than the inductor peak current. The inductor peak current,

IPEAK, is calculated using the following equation:

RIPPLE

MAX

LOAD

CHG

PEAK

Inductor conduction losses are caused by the flow of current

through the inductor, which has an associated internal dc

resistance (DCR). Larger inductors have smaller DCR values,

which may decrease inductor conduction losses. Inductor core

losses are related to the magnetic permeability of the core

material. Because the buck regulators are high switching

frequency dc-to-dc converters, shielded ferrite core material is

recommended for its low core losses and low electromagnetic

interference (EMI).

Boost Inductor Selection

The inductor is an essential part of the boost switching regulator. It

stores energy during the on time, and transfers that energy to

the output through the output rectifier during the off time. Use

inductance in the range of 2 µH to 10 µH. In general, lower

inductance values have higher saturation current and lower

series resistance for a given physical size. However, lower

inductance results in higher peak current that can lead to

reduced efficiency and greater input and/or output ripple and

noise. Peak-to-peak inductor ripple current at close to 30% of

the maximum dc input current typically yields an optimal

compromise. Suggested boost inductors are shown in Table 82.

The input VIN4 and output VOUT4 voltages determine the switch

duty cycle, which in turn determine the inductor ripple current.

Calculate the inductor ripple current in a steady state using the

following equation:

)

(

OUT4

IN4

OUT4

IN4

RIPPLE

−

Make sure that the peak inductor current, the maximum input

current plus half the inductor ripple current is below the rated

saturation current of the inductor. Likewise, make sure that the

maximum rated rms current of the inductor is greater than the

maximum dc input current to the regulator.

VBUSx Capacitor Selection

According to the USB 2.0 specification, USB peripherals have a

detectable change in capacitance on VBUSx when VBUSx are

attached. The peripheral device VBUSx bypass capacitance

must be at least 1 μF but not larger than 10 μF. The combined

capacitance for the VBUSx and CFL1 pins must not exceed

10 μF at any temperature or dc bias condition. Suggested

VBUSx capacitors are shown in Table 83.

CFL1 Capacitor Selection

The CFL1 pin serves the ADP5350 as the buck dc-to-dc

regulator input capacitor. The rms current rating of the input

capacitor current must be larger than the value calculated by the

following equation:

(

)

CFL1

ISOS

CFL1

ISOS

MAX

LOAD

CHG

RMS

)

(

−

To minimize supply noise, place the input capacitor as close as

possible to the CFL1 pin of the charger. As with the output

capacitor, a low ESR capacitor is recommended.

The effective capacitance needed for stability, which includes

temperature and dc bias effects, is a minimum of 2 µF and a

maximum of 7 µF. A list of suggested capacitors is shown in

Table 84.

Table 81. Suggested Buck Inductors

Vendor

Part Number

L (µH)

Typical DC Current (A)

Maximum DCR (mΩ)

Size

Wurth

74479976215

1.5

1.2

125

0806

TDK

VLS201612CX-1R5M

1.5

1.9

0806

Table 82. Suggested Boost Inductors

Vendor

Part Number

L (µH)

Typical DC Current (A)

Maximum DCR (mΩ)

Size

Wurth

74479776247A

4.7

0.9

140

0806

TDK

VLS201612CX-4R7M

4.7

1.12

252

0806

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