LT1937ES5 Linear Technology, LT1937ES5 Datasheet - Page 5

• Manufacturer Part Number: LT1937ES5
• Manufacturer: Linear Technology

Specifications of LT1937ES5

• Operating Supply Voltage (typ): 3.3/5/9V
• Number Of Segments: 6
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Package Type: TSOT-23
• Pin Count: 5
• Mounting: Surface Mount
• Operating Supply Voltage (min): 2.5V
• Operating Supply Voltage (max): 10V
• Lead Free Status / Rohs Status: Not Compliant

APPLICATIO S I FOR ATIO
Inductor Selection
A 22 H 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
PART NUMBER
LQH3C220
ELJPC220KF
CDRH3D16-220
LB2012B220M
LEM2520-220
Figure 4. Efficiency Comparison of Different Inductors
90
85
80
75
70
65
60
55
50
0
V
3LEDs
IN
2
= 3.6V
DCR
0.71
0.53
( )
4.0
1.7
5.5
4
U
LOAD CURRENT (mA)
6
MURATA LQH3C-220
PANASONIC ELJPC220KF
SUMIDA CDRH3D16-220
TAIYO YUDEN LB2012B220M
TAIYO YUDEN LEM2520-220
8
CURRENT
U
RATING
(mA)
250
160
350
125
10
75
12
14
W
16
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
18
1937 F04
20
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 1 F input capacitor and a 0.22 F output
capacitor are sufficient for most LT1937 applications.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
Taiyo Yuden
AVX
Murata
Kemet
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
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
PART
NUMBER
CMDSH-3
CMDSH2-3
BAT54
FORWARD VOLTAGE
CURRENT
(mA)
100
200
200
100mA
200mA
100mA
0.58 at
0.49 at
0.53 at
DROP
408-573-4150
843-448-9411
814-237-1431
408-986-0424
T
(V)
or C
PHONE
CAPACITANCE
D
) represents the switching
DIODE
7.0 at
15 at
10 at
(pF)
10V
10V
25V
URL
www.t-yuden.com
www.murata.com
www.avxcorp.com
www.kemet.com
MANUFACTURER
631-435-1110
www.centralsemi.com
Central
631-435-1110
www.centralsemi.com
Zetex
631-543-7100
www.zetex.com
Central
LT1937
5
1937f