LTC3450 Datasheet, PDF (9/12 Pages) Linear Technology – Triple Output Power Supply for Small TFT-LCD Displays

LTC3450
APPLICATIO S I FOR ATIO
Inductor Selection
Inductors in the range of 47µH to 100µH with saturation
current (I_SAT) ratings of at least 150mA are recommended
for use with the LTC3450. Ferrite core materials are
strongly recommended for their superior high frequency
performance characteristics. A bobbin or toroid type core
will reduce radiated noise. Inductors meeting these re-
quirements are listed in Table␣ 1.
Table 1. Recommended Inductors
PART
NUMBER
L MAX DCR HEIGHT
(µH) (Ω) (mm) VENDOR
CLQ4D10-470 47 1.28
CLQ4D10-101 100 3.15
CMD4D08-470 47 1.6
1.2 Sumida
[phone]
1.0 www.sumida.com
DO1606-473
DO1606-104
DT1608-473
DT1608-104
47 1.1
100 2.3
47 0.34
100 1.1
2.0 Coilcraft
[phone]
2.92 www.coilcraft.com
LQH43MN470J03 47 1.5
LQH43MN101J03 100 2.5
2.6 Murata
www.murata.com
DU6629-470M 47 0.64
DU6629-101M 100 1.27
2.92 Coev Magnetics
www.circuitprotection.com
Capacitor Selection
The boost converter requires two capacitors. The input
capacitor should be an X5R type of at least 1µF. The V_OUT
capacitor should also be an X5R type between 2.2µF and
10µF. A larger capacitor (10µF) should be used if lower
output ripple is desired or the output load required is close
to the 10mA maximum.
The charge pumps require flying capacitors of at least
0.1µF to obtain specified performance. Ceramic X5R types
are strongly recommended for their low ESR and ESL and
capacitance versus bias voltage stability. The filter capaci-
tor on V2X should be at least 0.1µF. A 0.47µF or larger
capacitor on V2X is recommended if V_INV is connected to
V2X. The filter capacitors on V3X and V_NEG should be
0.1µF or larger. Please be certain that the capacitors used
are rated for the maximum voltage with adequate safety
margin. Refer to Table 2 for a listing of capacitor vendors.
Table 2. Capacitor Vendor Information
Supplier
Phone
AVX
[phone]
Murata
[phone]
Taiyo Yuden
[phone]
Website
www.avxcorp.com
www.murata.com
www.t-yuden.com
Soft-Start
Soft-start operation provides a gradual increase in the
current drawn from the input power source (usually a
battery) during initial startup of the LTC3450, eliminating
the inrush current which is typical in most boost convert-
ers. This reduces stress on the input power source, boost
inductor and output capacitor, reduces voltage sag on the
battery and increases battery life. The rate at which the
input current will increase is set by two external compo-
nents (R_SS and C_SS) connected to SHDN (refer to Figure
2). Upon initial application of power or release of a pull
down switch on SHDN, the voltage on SHDN will increase
relative to the R • C time constant or R_SS␣ • C_SS. After one
time constant SHDN will rise to approximately 63.2% of
the voltage on V_IN. From 0V to approximately 0.65V on
SHDN, no switching will occur because the shutdown
threshold is 0.65V (typ). From 0.65V to 1V the maximum
switch pin current capability of the LTC3450 will gradually
increase from near zero to the maximum current limit. An
R_SS in the range of 1MΩ to 10MΩ is recommended. If
SHDN is driven high with a logic signal, the input current
will gradually increase to its maximum value in approxi-
mately 50µs.
V_IN
R_SS
1M
5%
C_SS
6.8nF
5 SHDN
1ms SOFT-START WITH 3.6V V_IN
3450 F02
Figure 2. Soft-Start Component Configuration
Printed Circuit Board Layout Guidelines
High speed operation of the LTC3450 demands careful
attention to PCB layout. You will not get advertised perfor-
mance with careless layout. Figure 3 shows the recom-
mended component placement for a single layer PCB. A
multilayer board with a separate ground plane is ideal but
not absolutely necessary.
3450f
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