LT3599
10
3599ff
For more information www.linear.com/LT3599
Inductor Selection
Table 1 lists several inductors that work well with the
LT3599, however, there are many other manufacturers and
devices that can be used. Consult each manufacturer for
detailed information on their entire range of parts. Ferrite
core inductors should be used to obtain the best efficiency.
Choose an inductor that can handle the necessary peak
current without saturating. Also, ensure that the inductor
has a low DCR (copper wire resistance) to minimize I
2
R
power losses. Values between 4.7µH and 22µH will suffice
for most applications.
Inductor manufacturers specify the maximum current
rating as the current where inductance falls by a given
percentage of its nominal value. An inductor can pass a
current greater than its rated value without damaging it.
Consult each manufacturer to determine how the maximum
inductor current is measured and how much more current
the inductor can reliably conduct.
Table 1. Recommended Inductors
PART
L
(µH)
MAX DCR
(Ω)
CURRENT
RATING (A) VENDOR
B1015AS-100M
817FY-4R7M
10
4.7
0.07
0.06
2.2
2.26
TOKO
www.toko.com
744065100
74454068
74454010
10
6.8
10
0.04
0.055
0.065
3
2.2
2
Würth Electronics
www.we-online.com
CDH115-100
CDH74NP-120L
CDH74NP-150L
10
12
15
0.028
0.065
0.083
3
2.45
2.10
Sumida
www.sumida.com
IHLP2020-BZ
IHLP2525-BD
10
10
0.184
0.116
2.3
2.5
Vishay
www.vishay.com
SHORTLED and OPENLED detection are disabled during
the start-up phase to avoid false flag generation. If an LED
string is open during normal operation, it will no longer
be used to regulate the output voltage. The output voltage
will regulate itself to find the LED string with the lowest
LED pin voltage. Fault detection (SHORTLED, OPENLED)
is updated when the PWM pin is high and latched when
the PWM pin is low.
During start-up, 11µA of current charges the external
soft-start capacitor. The SS pin directly limits the rate
of voltage rise on the V
C
pin, which in turn, limits the
peak switch current. Soft-start also enables switching
frequency foldback to provide a clean start-up for the
LT3599. Switch current limit protects the power switch
and external components.
operaTion
applicaTions inForMaTion
Capacitor Selection
Low ESR (equivalent series resistance) ceramic capaci-
tors should be used at the output to minimize the output
ripple voltage
.
Use only X5R or X7R dielectrics, as these
materials retain their capacitance over wider voltage and
temperature ranges than other dielectrics. A 4.7µF to 10µF
output capacitor is sufficient for most high output current
designs. Table 2 lists some suggested manufacturers.
Consult the manufacturers for detailed information on
their entire selection of ceramic parts.
Table 2. Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden (408) 573-4150
www.t-yuden.com
AVX (843) 448-9411
www.avxcorp.com
Murata (770) 436-1300
www.murata.com
Kemet (408) 986-0424
www.kemet.com
Diode Selection
Schottky diodes, with their low forward voltage drop and
fast switching speed, should be used for all LT3599 ap-
plications. Table 3 lists several Schottky diodes that work
well
.
The diode’s average current rating must exceed the
application’s average output current. The diode’s maximum
reverse voltage must exceed the application’s output volt
-
age. A 2A diode is sufficient for most designs. For PWM
dimming applications,
be aware of the reverse leakage
current of the diode. Lower leakage current will drain the
output capacitor less, allowing for higher dimming range.
