LT1937
W U U
APPLICATIO S I FOR ATIO
U
Capacitor Selection
Inductor 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.
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 2. Recommended Ceramic Capacitor Manufacturers
Table 1. Recommended Inductors
CURRENT
MANUFACTURER
Taiyo Yuden
AVX
PHONE
URL
408-573-4150
843-448-9411
814-237-1431
408-986-0424
www.t-yuden.com
www.avxcorp.com
www.murata.com
www.kemet.com
DCR
(Ω)
RATING
(mA)
PART NUMBER
MANUFACTURER
Murata
LQH3C220
0.71
4.0
250
160
350
75
Murata
814-237-1431
www.murata.com
Kemet
Diode Selection
ELJPC220KF
Panasonic
714-373-7334
www.panasonic.com
Schottky diodes, with their low forward voltage drop and
fast reverse recovery, are the ideal choices for LT1937
applications. TheforwardvoltagedropofaSchottkydiode
represents the conduction losses in the diode, while the
diode capacitance (CT or CD) 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.
CDRH3D16-220
LB2012B220M
LEM2520-220
0.53
1.7
Sumida
847-956-0666
www.Sumida.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
5.5
125
Taiyo Yuden
408-573-4150
www.t-yuden.com
90
85
80
75
70
65
60
55
50
V
= 3.6V
IN
3LEDs
Table 3. Recommended Schottky Diodes
FORWARD VOLTAGE
CURRENT DROP CAPACITANCE
DIODE
PART
NUMBER
(mA)
(V)
0.58 at
100mA
(pF)
7.0 at
10V
MANUFACTURER
Central
631-435-1110
www.centralsemi.com
Central
631-435-1110
www.centralsemi.com
Zetex
631-543-7100
www.zetex.com
MURATA LQH3C-220
CMDSH-3
CMDSH2-3
BAT54
100
PANASONIC ELJPC220KF
SUMIDA CDRH3D16-220
TAIYO YUDEN LB2012B220M
TAIYO YUDEN LEM2520-220
200
200
0.49 at
200mA
15 at
10V
0
2
4
6
8
10 12 14 16 18 20
LOAD CURRENT (mA)
1937 F04
0.53 at
100mA
10 at
25V
Figure 4. Efficiency Comparison of Different Inductors
1937f
5
Linear [ Linear ]
