AOZ1018 Ver la hoja de datos (PDF) - Alpha and Omega Semiconductor
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AOZ1018 Datasheet PDF : 14 Pages
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AOZ1018
For reliable operation and best performance, the input
capacitors must have current rating higher than ICINRMS
at worst operating conditions. Ceramic capacitors are
preferred for input capacitors because of their low ESR
and high ripple current rating. Depending on the applica-
tion circuits, other low ESR tantalum or electrolytic
capacitor may also be used. When selecting ceramic
capacitors, X5R or X7R type dielectric ceramic capaci-
tors are preferred for their better temperature and voltage
characteristics. Note that the ripple current rating from
capacitor manufactures are based on certain amount of
life time. Further de-rating may be necessary for practical
design requirement.
Inductor
The inductor is used to supply constant current to output
when it is driven by a switching voltage. For given input
and output voltage, inductance and switching frequency
together decide the inductor ripple current, which is,
∆IL
=
f--V--×---O--L--
×
1
–
V-V-----IO-N---
The peak inductor current is:
ILpeak
=
I
O
+
∆-----I--L-
2
High inductance gives low inductor ripple current but
requires larger size inductor to avoid saturation. Low
ripple current reduces inductor core losses. It also
reduces RMS current through inductor and switches,
which results in less conduction loss.
When selecting the inductor, make sure it is able to
handle the peak current without saturation even at the
highest operating temperature.
The inductor takes the highest current in a buck circuit.
The conduction loss on inductor needs to be checked for
thermal and efficiency requirements.
Surface mount inductors in different shape and styles are
available from Coilcraft, Elytone and Murata. Shielded
inductors are small and radiate less EMI noise. But they
cost more than unshielded inductors. The choice
depends on EMI requirement, price and size.
Table 2 lists some inductors for typical output voltage
design.
Output Capacitor
The output capacitor is selected based on the DC output
voltage rating, output ripple voltage specification and rip-
ple current rating.
The selected output capacitor must have a higher rated
voltage specification than the maximum desired output
voltage including ripple. De-rating needs to be consid-
ered for long term reliability.
Output ripple voltage specification is another important
factor for selecting the output capacitor. In a buck con-
verter circuit, output ripple voltage is determined by
inductor value, switching frequency, output capacitor
value and ESR. It can be calculated by the equation
below:
∆V O = ∆I L × ES RCO + 8-----×-----f---1-×-----C-----O--
Table 2. Typical Inductors
VOUT (V)
5.0
3.3
1.8
L1
Unshielded, 4.7µH LQH55DN4R7M03
Shielded, 4.7µH LQH66SN4R7M03
Shield, 5.8µH ET553-5R8
Un-shielded, 6.7µH DO3316P-682MLD
Unshielded, 4.7µH LQH55DN3R3M03
Shield, 4.7µH LQH66SN3R3M03
Shield, 3.3µH ET553-3R3
Un-shielded, 4.7µH DO3316P-472MLD
Un-shielded, 4.7µH DO1813P-472HC
Unshielded, 2.2µH LQH55DN1R5M03
Shield, 2.2µH LQH66SN1R5M03
Shield, 2.2µH ET553-2R2
Un-shielded, 2.2µH DO3316P-222MLD
Un-shielded, 2.2µH DO1813P-222HC
Rev. 1.0 November 2006
www.aosmd.com
Manufacture
MURATA
MURATA
ELYTONE
Coilcraft
MURATA
MURATA
ELYTONE
Coilcraft
Coilcraft
MURATA
MURATA
ELYTONE
Coilcraft
Coilcraft
Page 8 of 14
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