LT1937
APPLICATIO S I FOR ATIO
Inductor Selection
A 22µH inductor is recommended for most LT1937 appli-
cations. Although small size and high efficiency are major
concerns, the inductor should have low core losses at
1.2MHz and low DCR (copper wire resistance). Some
inductors in this category with small size are listed in
Table 1. The efficiency comparison of different inductors
is shown in Figure 4.
Table 1. Recommended Inductors
DCR
(Ω)
0.71
CURRENT
RATING
(mA)
250
PART NUMBER
LQH3C220
MANUFACTURER
Murata
814-237-1431
www.murata.com
Panasonic
714-373-7334
www.panasonic.com
Sumida
847-956-0666
www.Sumida.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
ELJPC220KF
4.0
160
CDRH3D16-220
0.53
350
LB2012B220M
1.7
75
LEM2520-220
5.5
125
90
V
IN
= 3.6V
85 3LEDs
80
EFFICIENCY (%)
75
70
65
60
55
50
0
2
4
6 8 10 12 14 16 18 20
LOAD CURRENT (mA)
1937 F04
MURATA LQH3C-220
PANASONIC ELJPC220KF
SUMIDA CDRH3D16-220
TAIYO YUDEN LB2012B220M
TAIYO YUDEN LEM2520-220
Figure 4. Efficiency Comparison of Different Inductors
U
Capacitor Selection
The small size of ceramic capacitors makes them ideal for
LT1937 applications. X5R and X7R types are recom-
mended because they retain their capacitance over wider
voltage and temperature ranges than other types such as
Y5V or Z5U. A 1µF input capacitor and a 0.22µF output
capacitor are sufficient for most LT1937 applications.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
Taiyo Yuden
AVX
Murata
Kemet
PHONE
408-573-4150
843-448-9411
814-237-1431
408-986-0424
URL
www.t-yuden.com
www.avxcorp.com
www.murata.com
www.kemet.com
W
U U
Diode Selection
Schottky diodes, with their low forward voltage drop and
fast reverse recovery, are the ideal choices for LT1937
applications. The forward voltage drop of a Schottky diode
represents the conduction losses in the diode, while the
diode capacitance (C
T
or C
D
) represents the switching
losses. For diode selection, both forward voltage drop and
diode capacitance need to be considered. Schottky diodes
with higher current ratings usually have lower forward
voltage drop and larger diode capacitance, which can
cause significant switching losses at the 1.2MHz switch-
ing frequency of the LT1937. A Schottky diode rated at
100mA to 200mA is sufficient for most LT1937 applica-
tions. Some recommended Schottky diodes are listed in
Table 3.
Table 3. Recommended Schottky Diodes
FORWARD VOLTAGE
DIODE
CURRENT DROP CAPACITANCE
(mA)
(V)
(pF)
MANUFACTURER
100
0.58 at
7.0 at
Central
100mA
10V
631-435-1110
www.centralsemi.com
CMDSH2-3
200
0.49 at
15 at
Central
200mA
10V
631-435-1110
www.centralsemi.com
BAT54
200
0.53 at
10 at
Zetex
100mA
25V
631-543-7100
www.zetex.com
PART
NUMBER
CMDSH-3
1937f
5
LINER [ LINEAR TECHNOLOGY ]
