aoz1050pi Alpha & Omega Semiconductor, aoz1050pi Datasheet - Page 10

• Manufacturer Part Number: aoz1050pi
• Description: Ezbucktm 2 A Synchronous 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
system crossover frequency is where the control loop
has unity gain. The crossover is the also called the
converter bandwidth. Generally a higher bandwidth
means faster response to load transients. 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
equal or less than 1/10 of the switching frequency.
The strategy for choosing R
over frequency with R
with C
calculate R
where;
f
f
V
G
200 x 10
G
8 A/V
The compensation capacitor C
make a zero. This zero is put somewhere close to the
dominate pole f
crossover frequency. C
The above equation can be simplified to:
An easy-to-use application software which helps to
design and simulate the compensation loop can be found
at www.aosmd.com.
C
C
C
f
C
R
FB
Z2
EA
CS
Rev. 1.0 June 2011
is the desired crossover frequency. For best performance,
is set to be about 1/10 of the switching frequency;
C
C
C
is 0.8V,
is the error amplifier transconductance, which is
is the current sense circuit transconductance, which is
=
=
=
=
C
. Using selected crossover frequency, f
-6
C
---------------------
-----------------------------------
2π
-----------------------------------
2π R
f
C
O
A/V, and
R
×
C
C
C
×
×
×
:
C
--------- -
V
to close the loop must be selected. The
and resistor R
C
V
1.5
R
1
FB
C
O
p1
C
L
×
×
but lower than 1/5 of the selected
×
R
f
P1
----------------------------- -
G
C
C
2π
EA
C
and set the compensator zero
can is selected by:
×
×
C
C
C
G
, is located at:
C
and C
CS
C
and resistor R
C
is to set the cross
C
C
, to
together
www.aosmd.com
Thermal Management and Layout
Considerations
In the AOZ1050PI buck regulator circuit, high pulsing
current flows through two circuit loops. The first loop
starts from the input capacitors, to the VIN pin, to the
LX pad, to 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 the inductor,
to the output capacitors and load, to the low side
NMOSFET. Current flows in the second loop when the
low side NMOSFET is on.
In PCB layout, minimizing the area of the two loops will
reduce the noise of the circuit and improves efficiency.
A ground plane is strongly recommended to connect the
input capacitor, the output capacitor, and the PGND pin
of the AOZ1050PI.
In the AOZ1050PI buck regulator circuit, the major power
dissipating components are the AOZ1050PI and the
output inductor. The total power dissipation of converter
circuit can be measured by input power minus output
power:
The power dissipation of the inductor can be
approximately calculated by the output current and DCR
value of the inductor:
The actual junction temperature can be calculated by the
power dissipation in the AOZ1050PI and the thermal
impedance from junction to ambient:
The maximum junction temperature of the AOZ1050PI is
150 ºC, which limits the maximum load current capability.
The thermal performance of the AOZ1050PI is strongly
affected by the PCB layout. Care should be taken during
the design process to ensure that the IC will operate
under the recommended environmental conditions.
P
T
P
inductor_loss
junction
total_loss
=
=
(
P
V
=
total_loss
IN
I
O
×
2
I
×
IN
R
–
inductor
–
P
V
inductor_loss
O
×
I
O
×
1.1
AOZ1050PI
) Θ
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JA