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LT1932ES6

Constant-Current DC/DC LED Driver in ThinSOT

Linear Technology 

LT1932

APPLICATIO S I FOR ATIO

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 4.7µH or 6.8µH inductor will be

a good choice for most LT1932 designs.

Table 1. Recommended Inductors

PART

MAX

L

DCR

(µH) (mΩ)

ELJEA4R7

ELJEA6R8

4.7 180

6.8 250

LQH3C4R7M24

LQH3C100M24

4.7 260

10 300

LB2016B4R7

LB2016B100

4.7 250

6.8 350

CMD4D06-4R7

CMD4D06-6R8

CLQ4D10-4R7

CLQ4D10-6R8

4.7 216

6.8 296

4.7 162

6.8 195

MAX

HEIGHT

(mm)

2.2

2.2

2.2

2.2

1.6

1.6

0.8

0.8

1.2

1.2

VENDOR

Panasonic

(714) 373-7334

www.panasonic.com

Murata

(814) 237-1431

www.murata.com

Taiyo Yuden

(408) 573-4150

www.t-yuden.com

Sumida

(847) 956-0666

www.sumida.com

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 1µH inductor will have

a lower DCR and a higher current rating than the 6.8µH

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 6.8µH

value.

85

80

SUMIDA

CLQ4D10-6R8

75

70

PANASONIC

ELJEA6R8

SUMIDA

CMD4D06-6R8

65 TAIYO YUDEN

LB2016B6R8

60

TAIYO YUDEN

LB2012B6R8

55

0

5

10

VIN = 3.6V

4 WHITE LEDs

ALL ARE 10µH

INDUCTORS

15

20

LED CURRENT (mA)

1932 F02

Figure 2. Efficiency for Several Different Inductor Types

85

80

6.8µH

75

22µH

4.7µH

70

2.2µH

65

60

55

0

VIN = 3.6V

4 WHITE LEDs

PANASONIC ELJEA

INDUCTORS

5

10

15

20

LED CURRENT (mA)

1932 F03

Figure 3. Efficiency for Several Different Inductor Values

1932f

5

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