ADP5140WACCZ-R7 datasheet(55/128 Pages) AD

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Data Sheet

ADP5140

Rev. 0 | Page 55 of 128

APPLICATIONS INFORMATION

INPUT CAPACITOR SELECTION

Higher value input capacitors help reduce the input voltage

ripple and improve transient response. To minimize supply

noise, place the input capacitors as close as possible to the

PVINx pins. The voltage rating of the input capacitors must

be greater than the maximum input voltage.

Input Capacitor Selection for the Buck Regulators

The input capacitors reduce the input voltage ripple caused by

the switch current on the power input pins. The loop composed

of the input capacitor, the high-side MOSFET, and the low-side

MOSFET must be kept as small as possible. A ceramic capacitor

with low ESR from 10 μF to 47 μF is recommended. Ensure that

the rms current rating of the input capacitor is larger than the

value calculated from the following equation:

)

CIN RMS BUCK

OUT BUCK

BUCK

×−

where

ICIN_RMS_BUCK is the rms current through the buck input capacitor.

IOUT_BUCK is the output current of the buck.

DBUCK is the duty cycle of buck regulator (DBUCK =

VOUT_BUCK/VIN_BUCK).

Input Capacitor Selection for the Boost Regulator

Because the input current of the boost regulator is continuous,

and the switch current on the power input pin is low, there are

no strict constraints on the input capacitor for the boost regulator.

A typical 10 μF ceramic capacitor with a voltage rating higher

than the input voltage is recommended.

Input Capacitor Selection for the LDO Regulators

Connect at least a 1 μF ceramic capacitor with low ESR from

PVINx pins to GND to reduce the circuit sensitivity to the PCB

layout, especially when long input traces or high source impedance

are encountered. If an output capacitance greater than 1 μF is

required, increase the input capacitor to match the capacitance.

INDUCTOR SELECTION

The inductor value is determined by the operating frequency,

input voltage, output voltage, and inductor ripple current.

Using a small inductor value leads to a faster transient response

but degrades efficiency because of a larger inductor ripple current.

Using a large inductor value leads to smaller ripple current and

better efficiency but results in a slower transient response.

Inductor Selection for the Buck Regulators

An inductor ranging from 0.33 µH to 1 µH is recommended for

the best balance between transient and efficiency performance.

The inductor ripple current, ΔIL_BUCK, is typically set to one-

third of the maximum load current.

Use the following equation to calculate the inductor value:

()

IN BUCK

OUT BUCK

BUCK

L BUCK

−×

∆×

where:

VIN_BUCK is the input voltage of buck regulator.

VOUT_BUCK is the output voltage of buck regulator.

ΔIL_BUCK is the inductor current ripple of buck regulator.

fSW is the switching frequency.

Use the following equation to calculate the peak inductor

current:

L BUCK

PEAK BUCK

OUT BUCK

∆

where:

IPEAK_BUCK is the peak inductor current of the buck.

The saturation current of the inductor must be larger than the

peak inductor current. For ferrite core inductors with a quick

saturation characteristic, the saturation current rating of the

inductor must be higher than the current-limit threshold of the

buck regulator to prevent the inductor from reaching saturation.

Use the following equation to calculate the rms current of the

inductor (IRMS_BUCK

IRMS_BUCK =

BUCK

OUT

∆

Shielded ferrite core materials are recommended for low core

loss and low EMI.

Inductor Selection for the Boost Regulator

An inductor from 2.2 µH to 10 µH is recommended for optimal

balance between transient and efficiency performance. The

inductor ripple current, ΔIL_BOOST, is typically set to 1/3 of the

average inductor current, IAVE_BOOST as follows:

OUT BOOST

AVE BOOST

BOOST

−

where:

IOUT_BOOST is the output current of the boost regulator.

DBOOST is the duty cycle of the boost regulator.

OUT BOOST

IN BOOST

BOOST

OUT BOOST

−

Use the following equation to calculate the inductor value:

IN BOOST

BOOST

L BOOST

∆×

where:

VIN_BOOST is the input voltage of boost regulator.

As the boost ratio increases (higher duty cycle), the average

inductor current increases dramatically. Ensure that the

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