ADP5310 datasheet(21/28 Pages) AD

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Data Sheet

ADP5310

Rev. A | Page 21 of 28

APPLICATIONS INFORMATION

This section describes the external components selection for the

ADP5310. The typical application circuit is shown in Figure 56.

SW1

PGND1

FB1

PWRGD

10µF

MLCC

4.7µH

VOUT1

PWRGD

SW2

PGND2

FB2

10µF

MLCC

4.7µH

VOUT2

ADP5310

EN1

FROM MCU

PVIN1

PVIN

PVIN2

EN3

SYNC/MODE

10µF

MLCC

VOUT3

220nF

MLCC

AGND

VREG

1µF

Figure 56. Typical Application Circuit

EXTERNAL COMPONENT SELECTION

Table 6, Table 7, and Table 8 list external component selections for

the ADP5310 application circuit. The selection of components is

dependent on the input voltage, output voltage, and load current

requirements. Additionally, trade-offs among performance

parameters, such as efficiency and transient response, are made

by varying the choice of external components.

SELECTING THE INDUCTOR

The high frequency switching of theADP5310 allows the use of

small surface-mount power inductors. The inductor value affects

the transition from PWM to PSM, efficiency, output ripple, and

current limit values. Use the following equation to calculate the

ideal inductance, which is derived from the inductor current

slope compensation, for a given output voltage and switching

frequency:

OUT

where:

L is the inductor value in μH.

VOUT is the output voltage for Channel 1 and Channel 2 of the

buck regulator.

k is 1.06 (Channel 1) or 0.478 (Channel 2).

fSW is the switching frequency in MHz (1.2 MHz typical).

The ripple current is calculated as follows:













−

∆

OUT

The dc resistance (DCR) value of the selected inductor affects

efficiency.A minimum requirement of the dc current rating of the

inductor is for it to be equal to the maximum load current plus

half of the inductor current ripple, as shown in the following

equation:











 ∆

)

(

MAX

LOAD

OUTPUT CAPACITOR

Output capacitance is required to minimize the voltage overshoot,

voltage undershoot, and the ripple voltage present on the output.

Capacitors with low equivalent series resistance (ESR) values

produce the lowest output ripple; Furthermore, use capacitors

such as the X5R and X7R dielectric. Do not use Y5V and Z5U

capacitors. Y5V and Z5U capacitors are unsuitable choices

because of their large capacitance variation over temperature and

their dc bias voltage changes. Because ESR is important, select

the capacitor using the following equation:

RIPPLE

COUT

ESR

∆

≤

where:

ESRCOUT is the ESR of the chosen capacitor.

VRIPPLE is the peak-to-peak output voltage ripple.

Use the following equation to determine the output capacitance:

RIPPLE

OUT

∆

≥

Increasing the output capacitor value has no effect on stability

and may reduce output ripple and enhance load transient response.

When choosing the output capacitor value, it is important to

account for the loss of capacitance due to output voltage dc bias.

INPUT CAPACITOR

An input capacitor is required to reduce input voltage ripple and

source impedance. Place the input capacitor as close as possible

to the PVINx pin.Alow ESR X7R or X5R type capacitor is highly

recommended to minimize the input voltage ripple. Use

the following equation to determine the rms input current:

OUT

MAX

LOAD

RMS

)

(

)

(

−

≥

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