CAT32

http://onsemi.com

7

Application Information

Inductor Selection and Efficiency

Inductor vendors are shown below. Contact the manufacturer for detailed technical data and new product information.

Table 5. INDUCTOR MANUFACTURERS

Inductor

L (mH)

Maximum DCR (mW)

Maximum

Height (mm)

Vendor

Web

ELJEA4R7

4.7

180

2.2

Panasonic

714.373.7334

www.panasonic.com

ELJEA6R8

6.8

250

2.2

LQH3C4R7M24,

4.7

260

2.2

Murata

770.436.1300

www.murata.com

LQH32CN4R7M11

LQH3C100K24,

10

300

2.2

LQH32CN100K11

LB2016B4R7

4.7

250

2.0

Taiyo Yuden

408.573.4150

www.t−yuden.com

LB2016B100

3.8

350

2.0

CMD4D06−4R7

4.7

216

0.8

Sumida

847.956.0666

www.sumida.com

CMD4D06−6R8

6.8

296

0.8

CLQ4D10−4R7

4.7

162

1.2

CLQ4D10−6R8

6.8

195

1.2

Capacitor Selection

Low ESR (equivalent series resistance) capacitors should

be used at the output to minimize the output ripple voltage.

The low ESR and small package options available with

multilayer ceramic capacitors make them excellent choices.

The X5R and X7R capacitor types are preferred because

they retain their capacitance over wider voltage and

temperature ranges than the Y5V or Z5U types. A 1.0

mF or

2.2

mF output capacitor is recommended for most

applications.

The voltage rating of the output capacitor C2 depends on

the number of LEDs driven in series. A 10 V ceramic

capacitor is recommended when driving two LEDs. A 16 V

ceramic capacitor is recommended when driving 3 or 4

LEDs.

Table 6. CERAMIC CAPACITOR MANUFACTURERS

Supplier

Phone

Web

Taiyo Yuden

408.573.4150

www.t−yuden.com

Murata

814.237.1431

www.murata.com

Kemet

408.986.0424

www.kemet.com

Low profile ceramic capacitors with a 1 mm maximum

height/thickness are available for designs height

requirements. Ceramic capacitors also make a good choice

for the input capacitor, which should be mounted as close as

possible to the CAT32. A 2.2

mF or 4.7 mF input capacitor is

recommended. Table 6 shows a list of several ceramic

capacitor manufacturers. Consult the manufacturers for

detailed information as new products and package options

are introduced regularly.

Diode Selection

Schottky diodes, with their low forward voltage drop and

fast switching speed, are the ideal choice for high efficiency

applications. Table 7 shows several different Schottky

diodes that work well with the CAT32. Make sure that the

diode has a voltage rating greater than the output voltage.

The diode conducts current only when the power switch is

turned off (typically less than one−third the time), so a 0.4 A

or 0.5 A diode will be sufficient for most designs.

Table 7. SCHOTTKY DIODE SUPPLIERS

Part

Supplier

MBR0520

ON Semiconductor

www.onsemi.com

800.282.9855

MBR0530 s

MBR0540

ZHCS400

Zetex

LED Current Programming

The LED current is programmed with a single resistor

connected to the RSET pin. The RSET pin is internally

regulated to 100 mV, which sets the current flowing out of

this pin, ISET, equal to 100 mV/RSET. The CAT32 regulates

values.