LTC3530 LINER [Linear Technology], LTC3530 Datasheet - Page 10

• Manufacturer Part Number: LTC3530
• Description: Wide Input Voltage Synchronous Buck-Boost DC/DC Converter
• Manufacturer: LINER [Linear Technology]

OPERATION
LTC3530
Soft-Start
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 V
A detailed diagram of this function is shown in Figure 3.
The components R
voltage on SHDN/SS to provide a soft-start function. To
ensure that V
raised above 1.6V.
COMPONENT SELECTION
Inductor Selection
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:
Table 1. Inductor Vendor Information
10
SUPPLIER
Coilcraft
CoEv Magnetics
Murata
Sumida
TDK
TOKO
L
L
BOOST
BUCK
>
>
V
V
OUT
C
SHDN/SS
IN(MIN)
is not being clamped, SHDN/SS must be
f • I
V
• (V
IN
SS
f • I
L
IN(MAX)
• (V
• V
and C
Figure 3.
PHONE
[phone]
[phone]
[phone]
[phone]
USA: [phone]
Japan: 81(3) 3607-5111
[phone]
[phone]
L
OUT
IN(MAX)
• V
– V
SS
– V
OUT
OUT
provide a slow ramping
IN(MIN)
)
3530 F05
H
V
V
CI
C
)
H
FAX
[phone]
[phone]
[phone]
USA: [phone]
Japan: 81(3) 3607-5144
[phone]
[phone]
C
.
where f = operating frequency, Hz
ΔI
V
V
V
I
For high effi ciency, 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 I
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 fi lter 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:
where C
f = switching frequency in Hz.
OUT(MAX)
IN(MIN)
IN(MAX)
OUT
L
% Ripple_Boost =
% Ripple_Buck =
I
8LCf
OUT(MAX)
= maximum allowable inductor ripple current, A
= output voltage, V
1
2
OUT
= minimum input voltage, V
= maximum input voltage, V
= maximum output load current
(V
2
IN(MAX)
C
= output fi lter capacitor in Farads and
R losses, and must be able to handle the peak
• (V
OUT
OUT
V
• V
IN(MAX)
– V
OUT
– V
WEB SITE
www.coilcraft.com
www.circuitprotection.com/magnetics.asp
www.murata.com
www.sumida.com
www.component.tdk.com
www.tokoam.com
OUT
IN(MIN)
2
• f
) • 100
) • 100
%
%
3530fb