8

LT1310

1310f

Inductor Selection

Several inductors that work well with the LT1310 are listed

in Table 2. This table is not exclusive; there are many other

manufacturers and inductors 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 high frequency are much lower for ferrite cores than for

the cheaper powdered-iron ones. Choose an inductor that

can handle at least 1.5A without saturating, and ensure

that the inductor has a low DCR (copper wire resistance)

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.

Switching frequency will also affect inductor require-

ments with higher frequencies corresponding to lower

inductance values. A good starting point is to set the

inductor ripple current equal to one-third of the peak

switch current.

The inductors shown in Table 2 were chosen for small size.

For better efficiency, use similar valued inductors with a

larger volume.

Table 2. Recommended Inductors

MAX

SIZE

L

DCR

L

× W × H

PART

(

µH) (mΩ)

(mm)

VENDOR

CDRH5D18-4R1

4.1

57

5.7

× 5.7 × 2 Sumida

CDRH5D18-5R4

5.4

76

(847) 956-0666

CDRH5D28-5R3

5.3

38

5.7

× 5.7 × 3 www.sumida.com

CDRH5D28-6R2

6.2

45

CDRH5D28-8R2

8.2

53

CR43-2R2

2.2

71

4.5

× 4 × 3.2

CR43-3R3

3.3

86

ELL6SH-4R7M

4.7

50

6.4

× 6 × 3

Panasonic

ELL6SH-5R6M

5.6

59

(408) 945-5660

ELL6SH-6R8M

6.8

62

www.panasonic.com

RLF5018T-4R7M1R4 4.7

45

5.6

× 5.2 × 1.8 TDK

RLF5018-1R5M2R1

1.5

25

5.2

× 5.6 × 1.8 (847) 803-6100

RLF5018-2R7M1R8

2.7

33

www.tdk.com

RLF5018-4R7M1R4

4.7

45

RLF5018-100MR94

10

67

LPO1704-122MC

1.2

80

5.5

× 6.6 × 1 Coilcraft

LPO1704-222MC

2.2

120

(800) 322-2645

www.coilcraft.com

APPLICATIO S I FOR ATIO

Capacitor Selection

Low ESR (equivalent series resistance) capacitors should

be used at the output to minimize the output ripple voltage.

Multilayer ceramic capacitors are an excellent choice, as

they have an extremely low ESR and are available in very

small packages. X5R dielectrics are preferred, followed by

X7R, as these materials retain the capacitance over wide

voltage and temperature ranges. A 4.7

µF to 20µF output

capacitor is sufficient for most applications, but systems

with very low output currents may need only a 1

µFor2.2µF

output capacitor. Solid tantalum or OS-CON capacitors

can be used, but they will occupy more board area than a

ceramic and will have a higher ESR. Always use a capacitor

with a sufficient voltage rating.

Ceramic capacitors also make a good choice for the input

decoupling capacitor, which should be placed as close as

possible to the LT1310. A 2.2

µF to 4.7µF input capacitor is

sufficient for most applications. Table 3 shows a list of

several ceramic capacitor manufacturers. Consult the

manufacturers for detailed information on their entire

selection of ceramic parts.

Table 3. Ceramic Capacitor Manufacturers

Taiyo Yuden

(408) 573-4150

www.t-yuden.com

AVX

(803) 448-9411

www.avxcorp.com

Murata

(714) 852-2001

www.murata.com

Compensation—Adjustment

To compensate the feedback loop of the LT1310, a series

resistor-capacitor network should be connected from the

range of 220pF to 1500pF will suffice. With a switching

frequency of 1.6MHz, a good starting value for the com-

technique to compensate a new application is to use a

30k

observing the transient response, the optimum value for

for the circuit of Figure 1 with a load current stepped from