ADP1883ARMZ-0.6-R7 datasheet(27/40 Pages) AD

27 / 40 page

ADP1882/ADP1883

Rev. 0 | Page 27 of 40

Diode Conduction Loss

The ADP1882/ADP1883 employ anticross conduction circuitry

that prevents the upper-side and lower-side MOSFETs from

conducting current simultaneously. This overlap control is

beneficial, avoiding large current flow that may lead to

irreparable damage to the external components of the power

stage. However, this blanking period comes with the trade-off of

a diode conduction loss occurring immediately after the

MOSFETs change states and continuing well into idle mode.

The amount of loss through the body diode of the lower-side

MOSFET during the antioverlap state is given by the following

expression:

)

(

)

(

LOAD

LOSS

BODY

LOSS

BODY

where:

tBODY(LOSS) is the body conduction time (refer to Figure 82 for

dead time periods).

tSW is the period per switching cycle.

VF is the forward drop of the body diode during conduction

(refer to the selected external MOSFET data sheet for more

information about the VF parameter).

2.7

5.5

4.8

4.1

3.4

VDD (V)

+125°C

+25°C

–40°C

1MHz

300kHz

()

Figure 82. Body Diode Conduction Time vs. Low Voltage Input (VDD)

Inductor Loss

During normal conduction mode, further power loss is caused

by the conduction of current through the inductor windings,

which have dc resistance (DCR). Typically, larger sized inductors

have smaller DCR values.

The inductor core loss is a result of the eddy currents generated

within the core material. These eddy currents are induced by the

changing flux, which is produced by the current flowing through

the windings. The amount of inductor core loss depends on the

core material, the flux swing, the frequency, and the core volume.

Ferrite inductors have the lowest core losses, whereas powdered

iron inductors have higher core losses. It is recommended to use

shielded ferrite core material type inductors with the ADP1882/

ADP1883 for a high current, dc-to-dc switching application

to achieve minimal loss and negligible electromagnetic

interference (EMI).

PDCR(LOSS) = DCR × I2LOAD + Core Loss

INPUT CAPACITOR SELECTION

The goal in selecting an input capacitor is to reduce or minimize

input voltage ripple and to reduce the high frequency source

impedance, which is essential for achieving predictable loop

stability and transient performance.

The problem with using bulk capacitors, other than their

physical geometries, is their large equivalent series resistance

(ESR) and large equivalent series inductance (ESL). Aluminum

electrolytic capacitors have such high ESR that they cause

undesired input voltage ripple magnitudes and are generally not

effective at high switching frequencies.

If bulk capacitors are to be used, it is recommended that multi-

layered ceramic capacitors (MLCC) be used in parallel, due to

their low ESR values. This dramatically reduces the input voltage

ripple amplitude as long as the MLCCs are mounted directly across

the drain of the upper-side MOSFET and the source terminal of

the lower-side MOSFET (see the Layout Considerations section).

Improper placement and mounting of these MLCCs may cancel

their effectiveness due to stray inductance and an increase in

trace impedance.

OUT

MAX

LOAD

RMS

CIN

−

The maximum input voltage ripple and maximum input capacitor

rms current occur at the end of the duration of 1 − D while the

upper-side MOSFET is in the off state. The input capacitor rms

current reaches its maximum at Time D. When calculating the

maximum input voltage ripple, account for the ESR of the input

capacitor as follows:

VMAX,RIPPLE = VRIPP + (ILOAD,MAX × ESR)

where:

VRIPP is usually 1% of the minimum voltage input.

ILOAD,MAX is the maximum load current.

ESR is the equivalent series resistance rating of the input

capacitor used.

Inserting VMAX,RIPPLE into the charge balance equation to

calculate the minimum input capacitor requirement gives

RIPPLE

MAX

LOAD

IN,min

)

(

−

RIPPLE

MAX

LOAD

IN,min

where D = 50%.

ADP1883ARMZ-0.6-R7 датащи(PDF) 27 Page - Analog Devices

ADP1883ARMZ-0.6-R7 датащи(HTML) 27 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

датащи скачать

ссылки URL