CAT4237_07 Datasheet, PDF (8/14 Pages) Catalyst Semiconductor – High Voltage CMOS Boost White LED Driver

CAT4237
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)
5
10
15
20
25
30
R₁ (Ω)
60
30
20
15
12
10
Doc. No. 5013, Rev. A
8
© 2007 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice