LT3754 데이터 시트보기 (PDF) - Linear Technology
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LT3754 Datasheet PDF : 30 Pages
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LT3754
Applications Information
Table 1. Inductor Manufacturers
Manufacturer
PHONE NUMBER
Sumida
408-321-9660
Würth Elektronik
605-886-4385
Vishay
402-563-6866
Coilcraft
847-639-6400
Coiltronics
561-998-4100
WEB
www.sumida.com
www.we-online.com
www.vishay.com
www.coilcraft.com
www.cooperet.com
Input Capacitor
The input capacitor of the LT3754 boost converter will sup-
ply the transient input current of the power inductor. Values
between 2.2µF and 10µF will work well for the LT3754. Use
only X5R or X7R ceramic capacitors to minimize variation
over voltage and temperature. If inductor input voltage is
required to operate near the minimum allowed operational
VIN for the I.C., a larger capacitor value may be required.
This is to prevent excessive input voltage ripple causing
dips below the minimum operating input voltage.
Output Capacitor
Low ESR ceramic capacitors should be used at the LT3754
converter output to minimize output ripple voltage. Use
only X5R or X7R dielectrics as these materials retain their
capacitance over wider voltage and temperature ranges
than other dielectrics. The output capacitance requirements
for several LED driver application circuits are shown in
the Applications Information section for various ILED,
VIN, VOUT, L and fOSC values. Some suggested capacitor
manufacturers are listed in Table 2.
Table 2. Ceramic Capacitor Manufacturers
Manufacturer
PHONE NUMBER WEB
TDK
516-535-2600
www.tdk.com
Kemet
408-986-0424
www.kemet.com
Murata
814-237-1431
www.murata.com
Taiyo Yuden
408-573-4150
t-yuden.com
AVX
843-448-9411
www.avxcorp.com
Schottky Rectifier
The external diode for the LT3754 boost converter must
be a Schottky diode, with low forward voltage drop
and fast switching speed. Table 3 lists several Schottky
manufacturers. The diodes average current rating must
exceed the application’s average output current. The
diode’s maximum reverse voltage must exceed the
maximum output voltage of the application. For PWM
dimming applications be aware of the reverse leakage of
the Schottky diode. Lower leakage current will drain the
output capacitor less during PWM low periods, allowing
for higher PWM dimming ratios. The companies below
offer Schottky diodes with high voltage and current ratings.
Table 3. Schottky Rectifier Manufacturers
Manufacturer
PHONE NUMBER WEB
Diodes, Inc.
805-446-4800
www.microsemi.com
On Semiconductor 888-743-7826
www.onsemi.com
Zetex
631-360-2222
www.zetex.com
Vishay Siliconix
402-563-6866
www.vishay.com
Power MOSFET Selection
Several MOSFET vendors are listed in Table 4. Consult the
factory applications department for other recommended
MOSFETs. The power MOSFET selected should have a
VDS rating which exceeds the maximum Overvoltage
Protection (OVP) level programmed for the application.
(See “Programming OVP level” in the Applications
Information section). The MOSFET should also have a
low enough total gate charge Qg (at 7V VGS) and a low
enough switching frequency (fOSC) to not exceed the
INTVCC regulator current limit, where loading on INTVCC
pin due to gate switching should obey,
IGATE = Qg • fOSC ≤ 44mA
3754fc
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