5
LT1932
APPLICATIO S I FOR ATIO
WU
UU
Inductor Selection
Several inductors that work well with the LT1932 are listed
in Table 1. Many different sizes and shapes are available.
Consult each manufacturer for more detailed information
and for their entire selection of related parts. As core
losses at 1.2MHz are much lower for ferrite cores that for
the cheaper powdered-iron ones, ferrite core inductors
should be used to obtain the best efficiency. Choose an
inductor that can handle at least 0.5A and ensure that the
inductor has a low DCR (copper wire resistance) to mini-
mize I2R power losses. A 4.7
H or 6.8H inductor will be
a good choice for most LT1932 designs.
Table 1. Recommended Inductors
MAX
L
DCR
HEIGHT
PART
(
H)
(m
)
(mm)
VENDOR
ELJEA4R7
4.7
180
2.2
Panasonic
ELJEA6R8
6.8
250
2.2
(714) 373-7334
www.panasonic.com
LQH3C4R7M24
4.7
260
2.2
Murata
LQH3C100M24
10
300
2.2
(814) 237-1431
www.murata.com
LB2016B4R7
4.7
250
2.0
Taiyo Yuden
LB2016B100
6.8
350
2.0
(408) 573-4150
www.t-yuden.com
CMD4D06-4R7
4.7
216
0.8
Sumida
CMD4D06-6R8
6.8
296
0.8
(847) 956-0666
CLQ4D10-4R7
4.7
162
1.2
www.sumida.com
CLQ4D10-6R8
6.8
195
1.2
Inductor Efficiency Considerations
Many applications have thickness requirements that re-
strict component heights to 1mm or 2mm. There are 2mm
tall inductors currently available that provide a low DCR
and low core losses that help provide good overall effi-
ciency. Inductors with a height of 1mm (and less) are
becoming more common, and a few companies have
introduced chip inductors that are not only thin, but have
a very small footprint as well. While these smaller induc-
tors will be a necessity in some designs, their smaller size
gives higher DCR and core losses, resulting in lower
efficiencies. Figure 2 shows efficiency for the Typical
Application circuit on the front page of this data sheet, with
several different inductors. The larger devices improve
efficiency by up to 12% over the smaller, thinner ones.
Keep this in mind when choosing an inductor.
The value of inductance also plays an important role in the
overall system efficiency. While a 1
H inductor will have
a lower DCR and a higher current rating than the 6.8
H
version of the same part, lower inductance will result in
higher peak currents in the switch, inductor and diode.
Efficiency will suffer if inductance is too small. Figure 3
shows the efficiency of the Typical Application on the front
page of this data sheet, with several different values of the
same type of inductor (Panasonic ELJEA). The smaller
values give an efficiency 3% to 5% lower than the 6.8
H
value.
Figure 2. Efficiency for Several Different Inductor Types
Figure 3. Efficiency for Several Different Inductor Values
LED CURRENT (mA)
0
55
EFFICIENCY
(%)
60
65
70
75
80
85
510
15
20
1932 F02
VIN = 3.6V
4 WHITE LEDs
ALL ARE 10
H
INDUCTORS
TAIYO YUDEN
LB2016B6R8
TAIYO YUDEN
LB2012B6R8
SUMIDA
CMD4D06-6R8
PANASONIC
ELJEA6R8
SUMIDA
CLQ4D10-6R8
LED CURRENT (mA)
0
55
EFFICIENCY
(%)
60
65
70
75
2.2
H
80
85
510
15
20
1932 F03
VIN = 3.6V
4 WHITE LEDs
PANASONIC ELJEA
INDUCTORS
6.8
H
22
H
4.7
H