CAT4237 Datasheet, PDF (8/13 Pages) Catalyst Semiconductor – High Voltage CMOS Boost White LED Driver

APPLICATION INFORMATION
External Component Selection
Capacitors
The CAT4237 only requires small ceramic
capacitors of 4.7uF 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
CAT4237
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
recommended 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
LED current (mA) R1 (Ω)
5
60
10
30
15
20
20
15
25
12
30
10
Table 1. Resistor R1 and LED current
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
8 of 13
Doc. No. 5013, Rev. A