CAT4237 datasheet(8/14 Pages) CATALYST

8 / 14 page

CAT4237

Doc. No. MD-5013, Rev. B

Characteristics subject to change without notice

APPLICATION INFORMATION

External Component Selection

Capacitors

The CAT4237 only requires small ceramic capacitors

of 4.7µF on the input and 0.22µF on the output. Under

normal condition, a 4.7µF input capacitor is sufficient.

For applications with higher output power, a larger

input capacitor of 10µF may be appropriate. X5R and

X7R capacitor types are ideal due to their stability

across temperature range.

Inductor

A 33µH inductor is recommended for most of the

CAT4237 applications. In cases where the efficiency

is critical, inductances with lower series resistance are

preferred. Inductors with current rating of 300mA or

higher are recommended for most applications.

Sumida CDRH3D16-330 33µH inductor has a rated

current of 320mA and a series resistance (D.C.R.) of

520mΩ typical.

Schottky Diode

The current rating of the Schottky diode must exceed

the peak current flowing through it. The Schottky

diode performance is rated in terms of its forward

voltage at a given current. In order to achieve the best

efficiency, this forward voltage should be as low as

possible. The response time is also critical since the

driver is operating at 1MHz. Central Semiconductor

Schottky diode CMDSH05-4 (500mA rated) is recom–

mended for most applications.

LED Current Setting

The LED current is set by the external resistor R1

connected between the feedback pin (FB) and

ground. The formula below gives the relationship

between the resistor and the current:

R1 = 0.3V/LED current

Table 1. Resistor R1 and LED current

LED current (mA)

R1 (Ω)

CAT4237 Datasheet(PDF) 8 Page - Catalyst Semiconductor