S8550 datasheet(12/31 Pages) SII

12 / 31 page

STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS

S-8550 Series

Rev.5.0_01



External Parts Selection

1. Inductor

The inductance (L value) has a strong influence on the maximum output current (IOUT) and efficiency (

η).

The peak current (IPK) increases by decreasing L and the stability of the circuit improves and IOUT increases. If

L is decreased further, the current drive capability of the external transistor is insufficient and IOUT decreases.

If the L value is increased, the loss due to IPK of the power MOS FET decreases and the efficiency becomes

maximum at a certain L value. Further increasing L decreases the efficiency due to the increased loss of the

DC resistance of the inductor.

The recommended L value for the S-8550 Series is 3.3

μH.

When selecting an inductor, note the allowable current of the inductor. If a current exceeding this allowable

current flows through the inductor, magnetic saturation occurs, substantially lowering the efficiency.

Therefore, select an inductor so that IPK does not exceed the allowable current. IPK is expressed by the

following equations in the discontinuous mode and continuous mode.

× fOSC × L × VIN

IPK = IOUT +

VOUT

× (VIN − VOUT)

fOSC

= Oscillation frequency

Table 7 Typical Inductors

Manufacturer

Part Number

L Value

Resistance

Rated Current

Dimensions

× W × H) [mm]

Taiyo Yuden Co., Ltd.

NR4018T3R3M

3.3

μH

0.07

Ω max.

1.23 A max.

4.0

× 4.0 × 1.8

NR3012T3R3M

3.3

μH

0.1

Ω max.

0.91 A max.

3.0

× 3.0 × 1.2

Sumida Corporation

CDRH3D16/HP-3R3

3.3

μH

0.085

Ω max.

1.40 A max.

4.0

× 4.0 × 1.8

CDRH2D11/HP-3R3

3.3

μH

0.173

Ω max.

0.9 A max.

3.2

× 3.2 × 1.2

TDK Corporation

VLF4012AT-3R3M

3.3

μH

0.12

Ω max.

1.3 A max.

3.7

× 3.5 × 1.2

VLF3010AT-3R3M

3.3

μH

0.17

Ω max.

0.87 A max.

2.6

× 2.8 × 1.0

FDK Corporation

MIP3226D3R3M

3.3

μH

0.104

Ω max.

1.2 A max.

3.2

× 2.6 × 1.0

MIPS2520D3R3M

3.3

μH

0.156

Ω max.

1.0 A max.

2.5

× 2.0 × 1.0

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