5

LT1937

1937f

Inductor Selection

A 22

µH 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

CURRENT

DCR

RATING

PART NUMBER

(

Ω)

(mA)

MANUFACTURER

LQH3C220

0.71

250

Murata

814-237-1431

www.murata.com

ELJPC220KF

4.0

160

Panasonic

714-373-7334

www.panasonic.com

CDRH3D16-220

0.53

350

Sumida

847-956-0666

www.Sumida.com

LB2012B220M

1.7

75

Taiyo Yuden

408-573-4150

www.t-yuden.com

LEM2520-220

5.5

125

Taiyo Yuden

408-573-4150

www.t-yuden.com

APPLICATIO S I FOR ATIO

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

µF input capacitor and a 0.22µF output

capacitor are sufficient for most LT1937 applications.

Table 2. Recommended Ceramic Capacitor Manufacturers

MANUFACTURER

PHONE

URL

Taiyo Yuden

408-573-4150

www.t-yuden.com

AVX

843-448-9411

www.avxcorp.com

Murata

814-237-1431

www.murata.com

Kemet

408-986-0424

www.kemet.com

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

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

PART

CURRENT

DROP

CAPACITANCE

NUMBER

(mA)

(V)

(pF)

MANUFACTURER

CMDSH-3

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

Figure 4. Efficiency Comparison of Different Inductors

LOAD CURRENT (mA)

0

90

85

80

75

70

65

60

55

50

16

1937 F04

4

8

12

20

14

2

6

10

18

MURATA LQH3C-220

PANASONIC ELJPC220KF

SUMIDA CDRH3D16-220

TAIYO YUDEN LB2012B220M

TAIYO YUDEN LEM2520-220

3LEDs