AOZ1284
Equation above can also be simplified to:
R
The thermal performance of the AOZ1284 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.
C
O
L
C
C
R
C
Easy to use application software which helps to
design and simulate the compensation loop can be
found at www.aosmd.com.
Several layout tips are listed below for the best
electric and thermal performance. The Figure 3 (a)
and (b) give the example of layout for AOZ1284A and
AOZ1284D respectively.
Thermal management and layout consideration
1. Do not use thermal relief connection to the VIN
and the GND pin. Pour a maximized copper area
to the GND pin and the VIN pin to help thermal
dissipation.
In the AOZ1284 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 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
GND pin of the AOZ1284, to the LX pins of the
AOZ1284. Current flows in the second loop when the
low side diode is on.
2. Input capacitor should be connected to the VIN
pin and the GND pin as close as possible.
3. Make the current trace from LX pins to L to Co to
the GND as short as possible.
4. Pour copper plane on all unused board area and
connect it to stable DC nodes, like VIN, GND or
VOUT.
In 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 GND pin of the
AOZ1284.
5. Keep sensitive signal trace such as trace
connected with FB pin and COMP pin far away
from the LX pins.
In the AOZ1284 buck regulator circuit, the three major
power dissipating components are the AOZ1284,
external diode and output inductor. The total power
dissipation of converter circuit can be measured by
input power minus output power.
P
VIN IIN VO IO
total _ loss
The power dissipation of inductor can be
approximately calculated by output current and DCR
of inductor.
2
P
I R
1.1
inductor
inductor _ loss
O
The power dissipation of diode is
VO
Pdiode _ loss IO VF 1
VIN
The actual AOZ1284 junction temperature can be
calculated with power dissipation in the AOZ1284 and
thermal impedance from junction to ambient.
P
P
P
diode _ loss
total _ loss
inductor _ loss
T
junction
T
JA
ambient
The maximum junction temperature of AOZ1284 is
145ºC, which limits the maximum load current
capability.
www.aosmd.com
Page 11 of 14
Rev. 0.5 March 2012
AOS [ ALPHA & OMEGA SEMICONDUCTORS ]
