Datasheet

LTC3459
8
3459fc
OPERATION
Inductor Selection
An inductor with a minimum value of 15μH is recommended
for use with the LTC3459. Values larger than 15μH will
result in lower ripple current and switching frequency.
High frequency ferrite core materials are strongly recom-
mended. Some inductors meeting these requirements are
listed in Table 1.
Table 1. Example Inductors
VENDOR/PART
L
(μH)
DCR (Ω)/
I
MAX
(mA)
DIMENSIONS
(mm)
CONTACT
INFORMATION
Chip Inductors
Murata
LQH31C
LQH32C-Low Profi le
22
22
3/160
0.7/250
3.2 × 1.6 × 1.8
3.2 × 2.5 × 1.6
www.murata.com
Taiyo Yuden
LB2016 15
22
33
0.7/130
1/105
1.7/85
2.0 × 1.6 × 1.6
www.t-yuden.com
[phone]
Toko
LLB2520 15
22
33
1.7/180
2.5/160
3.8/130
2.5 × 2.0 × 1.6
www.tokoam.com
[phone]
Coilcraft
DO3314
DO1606T
15
22
15
22
33
0.86/650
1.2/500
0.4/700
0.5/500
0.74/450
3.3 × 3.3 × 1.4
6.5 × 5.3 × 2.0
www.coilcraft.com
[phone]
Sumida
CMD4D06
CDRJ2D1BLD
15
22
33
15
22
33
0.5/400
0.8/300
1.3/240
0.175/350
0.255/300
0.37/240
6.6 × 5.8 × 0.8
3.2 × 3.2 × 2.0
www.sumida.com
[phone]
APPLICATIONS INFORMATION
Figure 4. Recommended Component
Placement for a Single-Layer Board
This is accomplished by varying the t
OFF
period by ap-
proximately 1/(V
OUT
– V
IN
). Due to propagation delays
and a 0.6μA bias current in the timer, the t
OFF
time can be
more accurately predicted as follows:
tns
pF V
A
VV
k
OFF
OUT IN
≈+
μ+
100
08 125
06
500
.•.
.
–
If V
OUT
is less than V
IN
, the t
OFF
delay is fi xed at approxi-
mately 750ns.
Capacitor Selection
The boost converter requires two capacitors. The input
capacitor should be an X5R type of at least 1.0μF. The V
OUT
capacitor should also be an X5R type between 2.2μF and
10μF. A larger capacitor should be used if lower peak-to-
peak output ripple and better line regulation is desired.
Table 2. Capacitor Vendor Information
SUPPLIER PHONE WEBSITE
AVX [phone] www.avxcorp.com
Murata [phone] www.murata.com
Taiyo Yuden [phone] www.t-yuden.com
TDK [phone] www.component.tdk.com
PCB Layout Guidelines
The high speed operation of the LTC3459 demands care-
ful attention to board layout. You will not get advertised
performance with a careless layout. Figure 4 shows the
recommended component placement for the TSOT ver-
sion of the part. A large ground pin copper area will help
to lower the chip temperature.
SW
GND
FB
1
2
3
6
5
4
V
IN
V
OUT
SHDN
SHDN
3459 F04
V
OUT
V
IN
RECOMMENDED COMPONENT
PLACEMENT. TRACES CARRYING
CURRENT ARE DIRECT. TRACE
AREA AT FB PIN IS SMALL. LEAD
LENGTH TO BATTERY IS SHORT