S-8550AA-M5T1X Datasheet, PDF (12/31 Pages) Seiko Instruments Inc – RECTIFICATION, PWM CONTROL SWITCHING REGULATORS

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.
I_PK = IOUT +
V_OUT × (V_IN − V_OUT)
2 × f_OSC × L × V_IN
fOSC = Oscillation frequency
Manufacturer
Taiyo Yuden Co., Ltd.
Sumida Corporation
TDK Corporation
FDK Corporation
Table 7 Typical Inductors
Part Number
L Value
DC
Resistance
NR4018T3R3M
3.3 μH 0.07 Ω max.
Rated Current
1.23 A max.
Dimensions
(L × W × H) [mm]
4.0 × 4.0 × 1.8
NR3012T3R3M
3.3 μH 0.1 Ω max. 0.91 A max. 3.0 × 3.0 × 1.2
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
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
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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