AOZ1017 데이터 시트보기 (PDF) - Alpha and Omega Semiconductor
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AOZ1017 Datasheet PDF : 16 Pages
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AOZ1017
0.5
0.4
ICIN_RMS(m) 0.3
IO
0.2
0.1
0
0
0.5
1
m
Figure 2. ICIN vs. Voltage Conversion Ratio
For reliable operation and best performance, the input
capacitors must have current rating higher than ICIN_RMS
at the worst operating conditions. Ceramic capacitors are
preferred for the input capacitors because of their low
ESR and high ripple current rating. Depending on the
application circuits, other low ESR tantalum capacitors or
aluminum electrolytic capacitors may be used. When
selecting ceramic capacitors, X5R or X7R type dielectric
ceramic capacitors are preferred for their better
temperature and voltage characteristics. Note that the
ripple current rating from capacitor manufactures are
based on certain usage lifetime. 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
=
--V-----O----
f ×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 a 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.
VOUT
5.0V
3.3V
1.8 V
L1
Shielded, 6.8µH,
MSS1278-682MLD
Shielded, 6.8µH
MSS1260-682MLD
Un-shielded, 4.7µH,
DO3316P-472MLD
Shielded, 4.7µH,
DO1260-472NXD
Shielded, 3.3µH,
ET553-3R3
Shielded, 2.2µH,
ET553-2R2
Unshielded, 3.3µH,
DO3316P-222MLD
Manufacturer
Coilcraft
Coilcraft
Coilcraft
Coilcraft
ELYTONE
ELYTONE
Coilcraft
Shielded, 2.2µH,
MSS1260-222NXD
Coilcraft
Output Capacitor
The output capacitor is selected based on the DC output
voltage rating, output ripple voltage specification and
ripple 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
converter 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--
where;
CO is output capacitor value, and
ESRCO is the Equivalent Series Resistor of output capacitor.
Rev. 1.0 July 2007
www.aosmd.com
Page 9 of 16
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