CAT4139TD-GT3 Datasheet, PDF (7/13 Pages) ON Semiconductor – 22V High Current Boost White LED Driver

DEVICE OPERATION
The CAT4139 is a fixed frequency (1MHz), low noise,
inductive boost converter that provides a constant
current with excellent line and load regulation. The
device uses a high-voltage CMOS power switch
between the SW pin and ground to energize the
inductor. When the switch is turned off, the stored
energy in the inductor is released into the load via the
Schottky diode.
The on/off duty cycle of the power switch is internally
adjusted and controlled to maintain a constant
regulated voltage of 0.3V across the feedback resistor
connected to the feedback pin (FB). The value of the
resistor sets the LED current accordingly (0.3V/R1).
During the initial power-up stage, the duty cycle of the
internal power switch is limited to prevent excessive
in-rush currents and thereby provide a “soft-start”
mode of operation.
In the event of an “Open LED” fault condition, where the
feedback control loop becomes open, the output voltage
will continue to increase. Once this voltage exceeds 24V,
an internal protection circuit will become active and place
the device into a very low power safe operating mode.
Thermal overload protection circuitry has been
included to prevent the device from operating at
unsafe junction temperatures above 150ºC. In the
event of a thermal overload condition the device will
automatically shutdown and wait till the junction
temperatures cools to 130ºC before normal operation
is resumed.
CAT4139
APPLICATION INFORMATION
EXTERNAL COMPONENT SELECTION
CAPACITORS
The CAT4139 only requires small ceramic capacitors
of 4.7μF on the input 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 22µH inductor is recommended for most of the
CAT4139 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 CDRH6D28-220 22µH inductor has a rated
current of 1.2A and a series resistance (D.C.R.) of
128mΩ 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
Table 1. Resistor R1 and LED Current
LED current (mA)
20
25
30
100
300
R1 [Ω]
15
12
10
3
1
© 2008 SCILLC. All rights reserved.
7
Characteristics subject to change without notice
Doc. No. MD-5032 Rev. B