AN1882

Application information

Doc ID 10209 Rev 4

17/30

5.1.3

Inductor

The inductor value fixes the ripple current flowing through the output capacitor. The ripple

current is usually fixed at 20%-30% of the output current and is approximately obtained by

the following formula:

Equation 13

through the inductor is given by:

Equation 14

It can be seen that if the inductor value decreases, the peak current (which has to be lower

than the current limit of the device) increases. This peak current must be lower than the

saturation current of the choke.

This is particularly important when using ferrite cores because they can hardly saturate (the

inductance value decreases abruptly when the saturation threshold is exceeded, causing an

abrupt increase of the current flowing through it). The inductor should be selected also

considering the system stability, (see the slope compensation paragraph). Moreover the

inductor selection should be made taking in account the inductor parasitic resistance,

because a too high value can decrease the efficiency. In the following table some inductor

manufacturers are listed.

Table 5.

Recommended output capacitors

Manufacturer

Series

Cap value (µF)

Rated voltage (V)

ESR (m.)

Panasonic

ECJ

10 to 47

6.3

10

Panasonic

EEF

22 to 47

6.3

60 to 90

TAIYO YUDEN

JMK

10 to 47

6.3

10

Sanyo POSCAP

TPA

47 to 100

6.3

80 to 100

Table 6.

Recommended inductors

Manufacturer

Series

Inductor value (µH)

Saturation current (A)

Coilcraft

DO1607C

6.8 to 15

0.72 to 0.96

DT1608C

6.8 to 15

0.6 to 1

LPO1704

6.8 to 10

0.8 to 0.9

DO1606T

6.8 to 10

1 to 1.1

Panasonic

ELL6RH

6.2 to 22

0.7 to 1.4

ELL6GM

6.8 to 10

0.93 to 1.1

Toko

D62CB

10 to 22

0.71 to 1.07

D62C

10 to 22

0.63 to 0.99

L

V

IN

V

OUT

–

()

I

Δ

---------------------------------- T

ON

⋅

=

I

PK

I

O

I

Δ

2

-----

+

=