LTC3530EMS データシートの表示（PDF） - Linear Technology
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LTC3530EMS Datasheet PDF : 16 Pages
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LTC3530
OPERATION
VIN
where f = operating frequency, Hz
SHDN/SS
VCI
VC
3530 F05
Soft-Start
Figure 3.
The soft-start function is combined with shutdown.
When the SHDN/SS pin is brought above 1V typical, the
IC is enabled but the EA duty cycle is clamped from VC.
A detailed diagram of this function is shown in Figure 3.
The components RSS and CSS provide a slow ramping
voltage on SHDN/SS to provide a soft-start function. To
ensure that VC is not being clamped, SHDN/SS must be
raised above 1.6V.
ΔIL = maximum allowable inductor ripple current, A
VIN(MIN) = minimum input voltage, V
VIN(MAX) = maximum input voltage, V
VOUT = output voltage, V
IOUT(MAX) = maximum output load current
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
COMPONENT SELECTION
Inductor 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:
The high frequency operation of the LTC3530 allows the
use of small surface mount inductors. The inductor ripple
current is typically set to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:
LBOOST
>
VIN(MIN)
f
•
•
(VOUT – VIN(MIN))
IL • VOUT
H
LBUCK
>
VOUT
f
• (VIN(MAX) – VOUT
• IL • VIN(MAX)
)
H
% Ripple_Boost =
IOUT(MAX) • (VOUT – VIN(MIN)
COUT • VOUT2 • f
)
•
100
%
% Ripple_Buck =
1
8LCf2
(VIN(MAX) – VOUT )
VIN(MAX)
•
100
%
where COUT = output filter capacitor in Farads and
Table 1. Inductor Vendor Information
f = switching frequency in Hz.
SUPPLIER
PHONE
FAX
WEB SITE
Coilcraft
(847) 639-6400
(847) 639-1469
www.coilcraft.com
CoEv Magnetics
(800) 227-7040
(650) 361-2508
www.circuitprotection.com/magnetics.asp
Murata
(814) 237-1431
(800) 831-9172
(814) 238-0409
www.murata.com
Sumida
USA: (847) 956-0666
Japan: 81(3) 3607-5111
USA: (847) 956-0702
Japan: 81(3) 3607-5144
www.sumida.com
TDK
(847) 803-6100
(847) 803-6296
www.component.tdk.com
TOKO
(847) 297-0070
(847) 699-7864
www.tokoam.com
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