aoz1012d Alpha & Omega Semiconductor, aoz1012d Datasheet - Page 8

• Manufacturer Part Number: aoz1012d
• Description: Ezbuck 3a Simple Regulator
• Manufacturer: Alpha & Omega Semiconductor

Table 2. Typical Inductors
For reliable operation and best performance, the input
capacitors must have current rating higher than I
at the 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 capacitors
or aluminum electrolytic capacitors 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 manufacturers is
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 the
output when it is driven by a switching voltage. For a
given input and output voltage, inductance and switching
frequency together decide the inductor ripple current,
which is:
I
CIN_RMS
I
Rev. 1.2 February 2007
L
I
O
=
(m)
----------- -
f
V
Figure 2. I
5.0V
3.3V
1.8V
V
OUT
O
L
0.5
0.4
0.3
0.2
0.1
0
0
1
CIN
–
--------- -
V
V
vs. Voltage Conversion Ratio
Shielded, 5.8µH, ET553-5R8
Un-shielded, 4.7µH, DO3316P-472MLD
Un-shielded, 4.7µH, DO3316P-472MLD
Un-shielded, 4.7µH, DO1813P-472HC
Shielded, 2.2uH, ET553-2R2
Un-shielded, 2.2µH, DO3316P-222MLD
Un-shielded, 2.2µH, DO1813P-222HC
IN
O
0.5
m
CIN_RMS
www.aosmd.com
L1
1
The peak inductor current is:
High inductance gives low inductor ripple current but
requires a larger size inductor to avoid saturation. Low
ripple current reduces inductor core losses. Low ripple
current also reduces RMS current through the inductor
and switches, which results in less conduction loss.
When selecting the inductor, make sure it is able to
handle the peak current at the highest operating temper-
ature without saturation.
The inductor takes the highest current in a buck circuit.
The conduction loss on the 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
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 con-
sidered 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
I
Lpeak
=
I
O
+
-------- -
2
I
L
ELYTONE
Coilcraft
Coilcraft
Coilcraft
ELYTONE
Coilcraft
Coilcraft
Manufacture
AOZ1012D
Page 8 of 15