LTC3442 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC3442
Linear Technology
'LTC3442' PDF : 20 Pages View PDF
LTC3442
APPLICATIONS INFORMATION
For high efficiency, choose a ferrite inductor with a high
frequency core material to reduce core loses. The induc-
tor should have low ESR (equivalent series resistance) to
reduce the I2R losses, and must be able to handle the peak
inductor current without saturating. Molded chokes or chip
inductors usually do not have enough core to support the
peak inductor currents in the 1A to 2A region. To minimize
radiated noise, use a shielded inductor. See Table 1 for a
suggested list of inductor suppliers.
Output Capacitor Selection
The bulk value of the output filter capacitor is set to reduce
the ripple due to charge into the capacitor each cycle. The
steady-state ripple due to charge is given by:
% RIPPLE_BOOST=
( ) IOUT(MAX) •
VOUT – VIN(MIN)
• 100
%
COUT • VOUT2 • f
% RIPPLE_BUCK =
( ) IOUT(MAX) •
VIN(MAX) – VOUT
• 100
%
COUT • VIN(MAX) • VOUT • f
where COUT = output filter capacitor in Farads and
f = switching frequency in Hz.
The output capacitance is usually many times larger than
the minimum value in order to handle the transient response
requirements of the converter. For a rule of thumb, the ratio
of the operating frequency to the unity-gain bandwidth of
the converter is the amount the output capacitance will
have to increase from the above calculations in order to
maintain the desired transient response.
The other component of ripple is due to the ESR (equiva-
lent series resistance) of the output capacitor. Low ESR
capacitors should be used to minimize output voltage
ripple. For surface mount applications, Taiyo Yuden or
TDK ceramic capacitors, AVX TPS series tantalum capaci-
tors or Sanyo POSCAP are recommended. See Table 2 for
contact information.
Input Capacitor Selection
Since VIN is the supply voltage for the IC, as well as the input
to the power stage of the converter, it is recommended to
place at least a 4.7µF, low ESR ceramic bypass capacitor
close to the VIN and SGND pins. It is also important to
minimize any stray resistance from the converter to the
battery or other power source.
Table 1. Inductor Vendor Information
SUPPLIER
PHONE
Coilcraft
(847) 639-6400
CoEv Magnetics
(800) 227-7040
Murata
(814) 237-1431
(800) 831-9172
Sumida
USA: (847) 956-0666
Japan: 81(3) 3607-5111
TDK
(847) 803-6100
TOKO
(847) 297-0070
Table 2. Capacitor Vendor Information
SUPPLIER
PHONE
AVX
(803) 448-9411
Murata
(814) 237-1431
(800) 831-9172
Sanyo
(619) 661-6322
Taiyo Yuden
(408) 573-4150
TDK
(847) 803-6100
FAX
(847) 639-1469
(650) 361-2508
(814) 238-0490
USA: (847) 956-0702
Japan: 81(3) 3607-5144
(847) 803-6296
(847) 699-7864
FAX
(803) 448-1943
(814) 238-0490
(619) 661-1055
(408) 573-4159
(847) 803-6296
For more information www.linear.com/LTC3442
WEB SITE
www.coilcraft.com
www.circuitprotection.com/magnetics.asp
www.murata.com
www.sumida.com
www.component.tdk.com
www.tokoam.com
WEB SITE
www.avxcorp.com
www.murata.com
www.sanyovideo.com
www.t-yuden.com
www.component.tdk.com
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