AOZ1012D Ver la hoja de datos (PDF) - Alpha and Omega Semiconductor
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AOZ1012D Datasheet PDF : 17 Pages
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0.5
0.5
0.4
0.3
I CIN_RMS(m)
IO
0.2
0.1
0
0
0
0
0.5
1
m
1
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
worst operating conditions. Ceramic capacitors are
preferred for input capacitors because of their low ESR
and high ripple current rating. Depending on the
application circuits, other low ESR tantalum capacitor
may also 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 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,
∆I L
=
VO × (1 − VO )
f ×L
VIN
The peak inductor current is:
I Lpeak
=
IO
+
∆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. Usually, peak to
peak ripple current on inductor is designed to be 20%
to 30% of output current.
^lwNMNOa
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 below lists some inductors for typical output
voltage design.
Table 2.
Vout L1
5.0 V Shield, 5.8uH
ET553-5R8
3.3 V
1.8 V
Un-shielded, 4.7uH
DO3316P-472MLD
Un-shielded, 4.7uH
DO3316P-472MLD
Un-shielded, 4.7uH
DO1813P-472HC
Shield, 2.2uH
ET553-2R2
Un-shielded, 2.2uH
DO3316P-222MLD
Un-shielded, 2.2uH
DO1813P-222HC
Manufacture
ELYTONE
Coilcraft
Coilcraft
Coilcraft
ELYTONE
Coilcraft
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
considered 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:
∆ VO
=
∆I L
× (ESRCO
+
8×
1
f × CO
)
April 2006
www.aosmd.com
Page 10 of 17
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