S-8550 SII [Seiko Instruments Inc], S-8550 Datasheet - Page 12

• Manufacturer Part Number: S-8550
• Description: STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECIFICATION, PWM CONTROL SWITCHING REGULATORS
• Manufacturer: SII [Seiko Instruments Inc]

12
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
S-8550/8551 Series
External Parts Selection
1. Inductor
The inductance (L value) has a strong influence on the maximum output current (I
The peak current (I
L is decreased further, the current drive capability of the external transistor is insufficient and I
If the L value is increased, the loss due to I
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-8550/8551 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 I
following equations in the discontinuous mode and continuous mode.
f
OSC
Taiyo Yuden Co., Ltd.
Sumida Corporation
TDK Corporation
FDK Corporation
= Oscillation frequency
Manufacturer
I
PK
= I
OUT
PK
) increases by decreasing L and the stability of the circuit improves and I
+
V
2 × f
OUT
NR4018T3R3M
NR3012T3R3M
CDRH3D16/HP-3R3
CDRH2D11/HP-3R3
VLF4012AT-3R3M
VLF3010AT-3R3M
MIP3226D3R3M
MIPS2520D3R3M
× (V
OSC
Part Number
× L × V
IN
− V
Seiko Instruments Inc.
OUT
PK
IN
Table 7 Typical Inductors
)
does not exceed the allowable current.
PK
of the power MOS FET decreases and the efficiency becomes
L Value
3.3 µH
3.3 µH
3.3 µH
3.3 µH
3.3 µH
3.3 µH
3.3 µH
3.3 µH
0.085 Ω max.
0.173 Ω max.
0.104 Ω max.
0.156 Ω max.
0.07 Ω max.
0.12 Ω max.
0.17 Ω max.
Resistance
0.1 Ω max.
DC
Rated Current
1.23 A max.
0.91 A max.
1.40 A max.
0.87 A max.
0.9 A max.
1.3 A max.
1.2 A max.
1.0 A max.
OUT
) and efficiency (η).
I
PK
is expressed by the
OUT
(L × W × H) [mm]
OUT
4.0 × 4.0 × 1.8
3.0 × 3.0 × 1.2
4.0 × 4.0 × 1.8
3.2 × 3.2 × 1.2
3.7 × 3.5 × 1.2
2.6 × 2.8 × 1.0
3.2 × 2.6 × 1.0
2.5 × 2.0 × 1.0
Dimensions
decreases.
Rev.2.1
increases. If
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