aoz1014 Alpha & Omega Semiconductor, aoz1014 Datasheet - Page 11

• Manufacturer Part Number: aoz1014
• Description: Ezbuck 5a Simple Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

The zero given by the external compensation network,
capacitor C
f
To design the compensation circuit, a target crossover
frequency f
crossover frequency is where control loop has unity gain.
The crossover frequency is also called the converter
bandwidth. Generally a higher bandwidth means faster
response to load transient. However, the bandwidth
should not be too high because of system stability
concerns. When designing the compensation loop,
converter stability under all line and load condition must
be considered.
Usually, it is recommended to set the bandwidth to be
less than 1/10 of switching frequency. The AOZ1014
operates at a fixed switching frequency range from
350kHz to 600kHz. The recommended crossover
frequency is less than 30kHz.
The strategy for choosing R
over frequency with R
with C
calculate R
where;
f
V
G
A/V, and
G
9.02 A/V.
The compensation capacitor C
make a zero. This zero is put somewhere close to the
dominate pole, f
crossover frequency. C
C
The previous equation can also be simplified to:
f
R
C
C
Z 2
C
FB
EA
CS
Rev. 1.0 December 2006
C
C
is the desired crossover frequency,
C
is 0.8V,
=
is the error amplifier transconductance, which is 200 x 10
is the current sense circuit transconductance, which is
=
=
=
=
C
30kHz
. Using selected crossover frequency, f
------------------------------------ -
2
f
C
----------------------
------------------------------------ -
2
C
O
R
C
C
C
:
C
for close loop must be selected. The system
-----------
V
R
and resistor R
C
V
1.5
R
1
FB
C
C
O
P1
L
, but lower than 1/5 of the selected
f
R
P 1
----------------------------- -
G
C
C
2
EA
C
and set the compensator zero
can is selected by:
C
C
C
G
,is located at:
and C
O
CS
C
and resistor R
C
is to set the cross
C
C
, to
together
www.aosmd.com
-6
An easy-to-use application software which helps to
design and simulate the compensation loop can be found
at www.aosmd.com.
Table 3 lists the values for a typical output voltage design
when output is 44µF ceramics capacitor.
Table 3.
Thermal Management and Layout
Consideration
In the AOZ1014 buck regulator circuit, high pulsing cur-
rent flows through two circuit loops. The first loop starts
from the input capacitors, to the V
the filter inductor, to the output capacitor and load, and
then returns to the input capacitor through ground.
Current flows in the first loop when the high side switch is
on. The second loop starts from inductor, to the output
capacitors and load, to the anode of Schottky diode, to
the cathode of Schottky diode. Current flows in the
second loop when the low side diode is on.
In PCB layout, minimizing the two loops area reduces the
noise of this circuit and improves efficiency. A ground
plane is strongly recommended to connect input capaci-
tor, output capacitor, and PGND pin of the AOZ1014.
In the AOZ1014 buck regulator circuit, the two major
power dissipating components are the AOZ1014, the
Schottky diode, and output inductor. The total power
dissipation of converter circuit can be measured by input
power minus output power.
The power dissipation in Schottky can be approximately
calculated as:
where;
V
The power dissipation of inductor can be approximately
calculated by output current and DCR of inductor.
P
P
P
FW_Schottky
diode_loss
total _loss
inductor _loss
V
1.8V
3.3V
OUT
5V
8V
is the Schottky diode forward voltage drop.
=
=
V
I
O
=
IN
2.2µH
3.3µH
5.6µH
I
10µH
O
L1
2
I
1 D
IN
–
R
–
inductor
V
O
V
51.1k
31.6k
49.9k
20k
IN
R
FW _Schottky
I
O
C
pin, to the LX pins, to
1.1
AOZ1014
Page 11 of 18
1.0nF
1.0nF
1.0nF
1.0nF
C
C