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0.3

0.4 0.45

0.35

0.5 0.6 0.7 0.8 0.9 1.0

1.5

2.0

2.5

3.0

20

30

35

25

40

45

50

60

70

80

90

100

200

150

L47

L68

L100

L150

L220

L330

H2200

L680

H1500

H1000

H680

H470

H330

H220

H150

L470

I

(A)

IND,DC

TL3577

100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR

SLVS633 – OCTOBER 2006

B. Identify Inductor Value

1. From Figure 6, identify the inductor code for the region indicated by the intersection of E

• T and I

code gives the inductor value in microhenries. The L or H prefix signifies whether the inductor is rated for a

maximum E

• T of 90 Vµs (L) or 250 Vµs (H).

2. If D < 0.85, go to step C. If D

≥ 0.85, calculate the minimum inductance needed to ensure the switching

regulator’s stability:

found in step 1, above, is too low; an appropriate inductor code should be obtained from Figure 6 as follows:

a.

b.

Find where E

• T intersects this inductor value to determine if it has an L or H prefix. If E • T intersects

both the L and H regions, select the inductor with an H prefix.

C. Inductor Selection

Select an inductor from Table 2 which cross references the inductor codes to the part numbers of the three

different manufacturers. The inductors listed in Table 2 have the following characteristics:

AIE (ferrite, pot-core inductors): Benefits of this type are low electromagnetic interference (EMI), small

physical size, and very low power dissipation (core loss).

Pulse (powdered iron, toroid core inductors): Benefits are low EMI and ability to withstand E

• T and peak

current above rated value better than ferrite cores.

Renco (ferrite, bobbin-core inductors): Benefits are low cost and best ability to withstand E

• T and peak

current above rated value. Be aware that these inductors generate more EMI than the other types, and this

may interfere with signals sensitive to noise.

A.

This chart assumes that the inductor ripple current inductor is approximately 20% to 30% of the average inductor

current (when the regulator is under full load). Greater ripple current causes higher peak switch currents and greater

output ripple voltage. Lower ripple current is achieved with larger value inductors. The factor of 20% to 30% is

chosen as a convenient balance between the two extremes.

Figure 6. Inductor Selection Graph

14

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