ADPL21610ECPZ datasheet(7/15 Pages) AD

7 / 15 page

Operation

Duty Cycle

The typical maximum duty cycle of the ADPL21610 is

94% . The duty cycle for a given application is given by:

DC =

| VOUT | + | VD | – | VIN |

| VOUT | + | VD | – | VCESAT |

where VD is the diode forward voltage drop and

VCESAT is, in the worst case, 330mV (at 1.1A).

The ADPL21610 can be used at higher duty cycles,

but must be operated in the discontinuous conduction

mode so that the actual duty cycle is reduced.

Setting Output Voltage

R1 and R2 determine the output voltage.

VOUT = 1.255V (1+ R1/R2)

Switching Frequency and Inductor Selection

The ADPL21610 switches at 1.3 MHz, allowing small-

valued inductors to be used. 4.7µH or 10µH will usually

suffice. Choose an inductor that can handle at least

1.2A without saturating, and ensure that the inductor

has a low DCR (copper-wire resistance) to minimize

I2R power losses. Note that in some applications, the

current handling requirements of the inductor can be

lower, such as in the SEPIC topology, where each

inductor only carries one-half of the total switch cur-

rent. For better efficiency, use similar valued inductors

with a larger volume. Many different sizes and shapes

are available from various manufacturers. Choose a

core material that has low losses at 1.3MHz, such as

a ferrite core.

Soft-Start

The soft-start feature provides a way to limit the

inrush current drawn from the supply upon start-up.

An internal 250k resistor charges the external soft-

start capacitor to 1.255V. After the capacitor reaches

0.15V, the rate of voltage rise at the output of the

comparator A1 tracks the rate of voltage rise of the

soft-start capacitor. This limits the inrush current drawn

from the supply during start-up. The soft-start feature

plays another important role in applications where the

switch will reach levels of 30V or higher. During start-

up, excessively high switch current, together with the

presence of high voltage, can overstress the switch.

A properly used soft-start feature will keep the switch

current from overshooting. This practice will greatly

improve the robustness of such designs. Once the

part is shut down, the soft-start capacitor is quickly

discharged to 0.4V, then slowly discharged through the

250kΩ resistor to ground. If the part is to be shut down

and re-enabled within a short period of time while using

soft-start, you must ensure that the soft-start capacitor

has sufficient time to discharge before re-enabling the

part. Typical values of the soft-start capacitor range

from 10nF to 200nF.

Capacitor Selection

Low Equivalent series resistance (ESR) capacitors

should be used at the output to minimize the output

ripple voltage. Multi-layer ceramic capacitors are an

excellent choice, as they have extremely low ESR and

are available in very small packages. X5R dielectrics

are preferred, followed by X7R, as these materials

retain their capacitance over a wide range of voltages

and temperatures. A 4.7µF to 15µF output capacitor

is sufficient for most applications; however, systems

with very low output currents may require only a 1µF

or 2.2µF output capacitor. Solid tantalum or OS-CON

capacitors can be used, but they will occupy more

board area than ceramic capacitors and will have a

higher ESR. Always use a capacitor with a sufficient

voltage rating.

Ceramic capacitors also make a good choice for the

input decoupling capacitor, which should be placed as

close as possible to the ADPL21610. A 1µF to 4.7µF

input capacitor is sufficient for most applications.

Table 2

lists several ceramic capacitor manufacturers.

Consult the manufacturers for detailed information on

their entire selection of ceramic parts.

www.analog.com

Analog Devices │ 7

ADPL21610

1.1A Step-Up DC/DC

Converter with Integrated Soft-Start

Table 1. Inductor Manufacturers

MANUFACTURER

WEB

Sumida

www.sumida.com

TDK

www.tdk.com

Murata

www.murata.com

FDK

www.fdk.co.jp

Table 2. Ceramic Capacitor Manufacturers

MANUFACTURER

WEB

Taiyo Yuden

www.t-yuden.com

AVX

www.avxcorp.com

Murata

ADPL21610ECPZ Datasheet(PDF) 7 Page - Analog Devices

ADPL21610ECPZ Datasheet(HTML) 7 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Datasheet Download

Link URL