W-52 Datasheet, PDF (7/11 Pages) Copal Electronics – CMOS White LED Driver

W-52
Application Information
Inductor Selection and Efficiency
Inductor vendors are shown below. Contact the manufacturer for detailed technical data and new product information.
Table 5. INDUCTOR MANUFACTURERS
Inductor
ELJEA4R7
ELJEA6R8
LQH3C4R7M24,
LQH32CN4R7M11
LQH3C100K24,
LQH32CN100K11
LB2016B4R7
LB2016B100
CMD4D06ï4R7
CMD4D06ï6R8
CLQ4D10ï4R7
CLQ4D10ï6R8
L ( H)
4.7
6.8
4.7
10
4.7
3.8
4.7
6.8
4.7
6.8
Maximum DCR (m )
180
250
260
300
250
350
216
296
162
195
Maximum
Height (mm)
2.2
2.2
2.2
2.2
2.0
2.0
0.8
0.8
1.2
1.2
Vendor
Panasonic
714.373.7334
Murata
770.436.1300
Taiyo Yuden
408.573.4150
Sumida
847.956.0666
Web
www.panasonic.com
www.murata.com
www.tïyuden.com
www.sumida.com
Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used at the output to minimize the output ripple voltage.
The low ESR and small package options available with
multilayer ceramic capacitors make them excellent choices.
The X5R and X7R capacitor types are preferred because
they retain their capacitance over wider voltage and
temperature ranges than the Y5V or Z5U types. A 1.0 F or
2.2 F output capacitor is recommended for most
applications.
The voltage rating of the output capacitor C2 depends on
the number of LEDs driven in series. A 10 V ceramic
capacitor is recommended when driving two LEDs. A 16 V
ceramic capacitor is recommended when driving 3 or 4
LEDs.
Table 6. CERAMIC CAPACITOR MANUFACTURERS
Supplier
Phone
Web
Taiyo Yuden
408.573.4150
www.tïyuden.com
Murata
814.237.1431
www.murata.com
Kemet
408.986.0424
www.kemet.com
Low profile ceramic capacitors with a 1 mm maximum
height/thickness are available for designs height
requirements. Ceramic capacitors also make a good choice
for the input capacitor, which should be mounted as close as
possible to the W-52. A 2.2 F or 4.7 F input capacitor is
recommended. Table 6 shows a list of several ceramic
capacitor manufacturers. Consult the manufacturers for
detailed information as new products and package options
are introduced regularly.
Diode Selection
Schottky diodes, with their low forward voltage drop and
fast switching speed, are the ideal choice for high efficiency
applications. Table 7 shows several different Schottky
diodes that work well with the W-52. Make sure that the
diode has a voltage rating greater than the output voltage.
The diode conducts current only when the power switch is
turned off (typically less than oneïthird the time), so a 0.4 A
or 0.5 A diode will be sufficient for most designs.
Table 7. SCHOTTKY DIODE SUPPLIERS
Part
Supplier
MBR0520
MBR0530 s
MBR0540
ON Semiconductor
www.onsemi.com
800.282.9855
ZHCS400
Zetex
LED Current Programming
The LED current is programmed with a single resistor
connected to the RSET pin. The RSET pin is internally
regulated to 100 mV, which sets the current flowing out of
this pin, ISET, equal to 100 mV/RSET. The W-52 regulates
the current into the LED pin, I_LED, to 225 times the value of
I_SET. For the best accuracy, a 1% or better resistor is
recommended. Table 8 shows several typical 1% R_SET
values.
7