5

LT1930/LT1930A

LT1930 AND LT1930A DIFFERENCES

Switching Frequency

The key difference between the LT1930 and LT1930A is

the faster switching frequency of the LT1930A. At 2.2MHz,

the LT1930A switches at nearly twice the rate of the

LT1930. Care must be taken in deciding which part to use.

The high switching frequency of the LT1930A allows

smaller cheaper inductors and capacitors to be used in a

given application, but with a slight decrease in efficiency

and maximum output current when compared to the

LT1930. Generally, if efficiency and maximum output

current are critical, the LT1930 should be used. If applica-

tion size and cost are more important, the LT1930A will be

the better choice. In many applications, tiny inexpensive

chip inductors can be used with the LT1930A, reducing

solution cost.

Duty Cycle

The maximum duty cycle (DC) of the LT1930A is 75%

compared to 84% for the LT1930. The duty cycle for a

given application using the boost topology is given by:

DC

VV

V

OUT

IN

OUT

=

|| – |

|

||

For a 5V to 12V application, the DC is 58.3% indicating that

the LT1930A could be used. A 5V to 24V application has

a DC of 79.2% making the LT1930 the right choice. The

LT1930A can still be used in applications where the DC, as

calculated above, is above 75%. However, the part must

be operated in the discontinuous conduction mode so that

the actual duty cycle is reduced.

INDUCTOR SELECTION

Several inductors that work well with the LT1930 are listed

in Table 1 and those for the LT1930A are listed in Table 2.

These tables are not complete, and there are many other

manufacturers and devices that can be used. Consult each

manufacturer for more detailed information and for their

entire selection of related parts, as many different sizes and

shapes are available. Ferrite core inductors should be used

to obtain the best efficiency, as core losses at 1.2MHz are

much lower for ferrite cores than for cheaper powdered-

iron types. Choose an inductor that can handle at least 1A

without saturating, and ensure that the inductor has a low

A 4.7

µH or 10µH inductor will be the best choice for most

LT1930 designs. For LT1930A designs, a 2.2

µH to 4.7µH

inductor will usually suffice. Note that in some applica-

tions, the current handling requirements of the inductor

can be lower, such as in the SEPIC topology where each

inductor only carries one-half of the total switch current.

Table 1. Recommended Inductors – LT1930

MAX

SIZE

L

DCR

L

× W × H

PART

(

µH)

m

Ω

(mm)

VENDOR

CDRH5D18-4R1

4.1

57

4.5

× 4.7 × 2.0 Sumida

CDRH5D18-100

10

124

(847) 956-0666

CR43-4R7

4.7

109

3.2

× 2.5 × 2.0 www.sumida.com

CR43-100

10

182

DS1608-472

4.7

60

4.5

× 6.6 × 2.9 Coilcraft

DS1608-103

10

75

(847) 639-6400

www.coilcraft.com

ELT5KT4R7M

4.7

240

5.2

× 5.2 × 1.1 Panasonic

ELT5KT6R8M

6.8

360

(408) 945-5660

www.panasonic.com

Table 2. Recommended Inductors – LT1930A

MAX

SIZE

L

DCR

L

× W × H

PART

(

µH)

m

Ω

(mm)

VENDOR

LQH3C2R2M24

2.2

126

3.2

× 2.5 × 2.0 Murata

LQH3C4R7M24

4.7

195

(404) 573-4150

www.murata.com

CR43-2R2

2.2

71

4.5

× 4.0 × 3.0 Sumida

CR43-3R3

3.3

86

(847) 956-0666

www.sumida.com

1008PS-272

2.7

100

3.7

× 3.7 × 2.6 Coilcraft

1008PS-332

3.3

110

(800) 322-2645

www.coilcraft.com

ELT5KT3R3M

3.3

204

5.2

× 5.2 × 1.1 Panasonic

(408) 945-5660

www.panasonic.com

The inductors shown in Table 2 for use with the LT1930A

were chosen for small size. For better efficiency, use

similar valued inductors with a larger volume. For

example, the Sumida CR43 series in values ranging from

2.2

µH to 4.7µH will give an LT1930A application a few

percentage points increase in efficiency, compared to the

smaller Murata LQH3C Series.