CAT4240_0711 Datasheet, PDF (8/14 Pages) Catalyst Semiconductor – 6 Watt Boost LED Driver

CAT4240
APPLICATION INFORMATION
External Component Selection
Capacitors
The CAT4240 only requires small ceramic capacitors
of 4.7μF on the inductor input, 1µF on the VIN pin and
1µF 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 47µH inductor is recommended for most of the
CAT4240 applications. In cases where the efficiency
is critical, inductances with lower series resistance are
preferred. Inductors with current rating of 800mA or
higher are recommended for most applications.
Sumida CDRH6D28-470 47µH inductor has a rated
current of 800mA and a series resistance (D.C.R.) of
176mΩ 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 rectifier CMSH1-40 (1A 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)
20
25
30
100
300
R1 (Ω)
15
12
10
3
1
Table 1. Resistor R1 and LED current
Doc. No. MD-5026 Rev. C
8
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice