aoz1094 Alpha & Omega Semiconductor, aoz1094 Datasheet - Page 12

• Manufacturer Part Number: aoz1094
• Description: Ezbucktm 5a Simple Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

The zero given by the external compensation network,
capacitor C
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
concern. 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. AOZ1094
operates at a fixed switching frequency range from
350kHz to 600kHz. It is recommended to choose a
crossover frequency 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. CC can is selected by:
The previous equation can also be simplified to:
f
C
f
C
C
R
C
FB
Z2
EA
CS
Rev. 1.3 October 2010
is the desired crossover frequency,
C
C
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
-----------------------------------
2π
-----------------------------------
2π R
C
---------------------
f
C
O
R
×
C
C
C
×
×
×
:
C
for close loop must be selected. The system
--------- -
V
and resistor R
C
V
1.5
R
1
FB
C
O
C
p1
L
×
×
but lower than 1/5 of selected
×
R
f
P1
----------------------------- -
G
C
C
2π
EA
and set the compensator zero
×
×
C
C
C
G
, is located at:
O
and C
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 typical output voltage design
when output is 10µF ceramics capacitor and 100µF
tantalum capacitor.
Table 3.
Thermal Management and Layout
Consideration
In the AOZ1094 buck regulator circuit, high pulsing
current flows through two circuit loops. The first loop
starts from the input capacitors, to the V
LX pins, to the filter inductor, to the output capacitor and
load, and then return 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
capacitor, output capacitor, and PGND pin of the
AOZ1094.
In the AOZ1094 buck regulator circuit, the major power
dissipating components are the AOZ1094, 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
P
P
FW_Schottky
diode_loss
total_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
10µH
×
L1
×
(
I
1 D
IN
–
–
V
) V
O
×
×
51.1k
31.6k
49.9k
20k
FW_Schottky
I
R
O
C
Ω
Ω
Ω
Ω
IN
pin, to the
AOZ1094
Page 12 of 19
1.0nF
1.0nF
1.0nF
1.0nF
C
C