aoz1056 Alpha & Omega Semiconductor, aoz1056 Datasheet - Page 11

• Manufacturer Part Number: aoz1056
• Description: Ezbucktm 2a Simple Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

Usually, it is recommended to set the bandwidth to be
less than 1/10 of switching frequency. It is recommended
to choose a crossover frequency less than 34kHz.
The strategy for choosing R
over frequency with R
with C
calculate R
where;
f
V
G
A/V, and
G
5.64 A/V.
The compensation capacitor C
make a zero. This zero is put somewhere close to the
dominate pole fp1 but lower than 1/5 of selected
crossover frequency. C
The previous equation above can also 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.
Thermal Management and Layout
Consideration
In the AOZ1056 buck regulator circuit, high pulsing
current flows through two circuit loops. The first loop
starts from the input capacitors, to the V
pin, 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 PGND pin of the AOZ1056, to
the LX pin of the AZO1056. Current flows in the second
loop when the low side diode is on.
C
C
C
R
FB
f
EA
CS
Rev. 1.2 September 2008
C
is desired crossover frequency,
C
C
C
is 0.8V,
is the error amplifier transconductance, which is 200x10
is the current sense circuit transconductance, which is
=
=
=
=
C
. Using selected crossover frequency, f
34kHz
---------------------------------- -
2π
f
C
---------------------
C
O
C
×
R
×
:
×
C
--------- -
V
V
1.5
R
R
FB
O
C
L
×
×
f
----------------------------- -
G
p1
C
2π
EA
C
and set the compensator zero
can is selected by:
×
×
C
C
G
and C
O
CS
C
and resistor R
C
is to set the cross
IN
pin, to the LX
C
C
, to
together
www.aosmd.com
-6
In the PCB layout, minimizing the two loops area reduces
the noise of this circuit and improves efficiency. A ground
plane is recommended to connect input capacitor, output
capacitor, and PGND pin of the AOZ1056.
In the AOZ1056 buck regulator circuit, the two major
power dissipating components are the AOZ1056 and
output inductor. The total power dissipation of converter
circuit can be measured by input power minus output
power.
The power dissipation of inductor can be approximately
calculated by output current and DCR of inductor.
The actual AOZ1056 junction temperature can be
calculated with power dissipation in the AOZ1056 and
thermal impedance from junction to ambient.
The maximum junction temperature of AOZ1056 is
150°C, which limits the maximum load current capability.
The thermal performance of the AOZ1056 is strongly
affected by the PCB layout. Extra care should be taken
by users during design process to ensure that the IC
will operate under the recommended environmental
conditions.
Several layout tips are listed below for the best electric
and thermal performance. Figure 3 below illustrates a
single layer PCB layout example as reference.
1. Do not use thermal relief connection to the V
2. Input capacitor should be connected to the V
3. A ground plane is preferred. If a ground plane is
4. Make the current trace from LX pin to L to Co to the
T
(
P
P
P
junction
inductor_loss
total_loss
total_loss
the PGND pin. Pour a maximized copper area to
the PGND pin and the V
dissipation.
and the PGND pin as close as possible.
not used, separate PGND from AGND and connect
them only at one point to avoid the PGND pin noise
coupling to the AGND pin. In this case, a decoupling
capacitor should be connected between V
AGND pin.
PGND as short as possible.
=
–
=
P
V
diode_loss
=
IN
I
O
×
×
I
IN
(
1 D
–
–
–
V
IN
P
O
pin to help thermal
) V
inductor_loss
×
×
I
O
FW_Schottky
AOZ1056
Page 11 of 15
) Θ
×
IN
pin and
IN
IN
JA
and
pin
+
T
amb