aoz1025di Alpha & Omega Semiconductor, aoz1025di Datasheet - Page 11

• Manufacturer Part Number: aoz1025di
• Description: Ezbucktm 8a Synchronous Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

Thermal Management and Layout
Consideration
In the AOZ1025 buck regulator circuit, the major power
dissipating components are the AOZ1025 output
inductor, and low-side NMOSFET. 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 power dissipation of low-side NMOSFET can be
approximately calculated by output current, Rdson, and
duty cycle (V
The actual junction temperature can be calculated with
power dissipation in the AOZ1025 and thermal
impedance from junction to ambient.
The thermal performance of the AOZ1025D is strongly
affected by the PCB layout. Extra care should be taken
by users during design to ensure that the IC will operate
under the recommended environmental conditions.
P
T
P
P
Rev. 1.3 September 2009
inductor_loss
junction
inductor_loss
total_loss
=
O
=
(
/ V
P
V
=
total_loss
=
IN
IN
I
I
).
O
O
2
×
2
×
×
I
IN
R
R
inductor
inductor
–
–
V
P
O
inductor_loss
×
I
×
O
×
⎛
⎜
⎝
1.1
1
Figure 3. AOZ1025D (DFN 5x4) PCB Layout
–
-------- -
V
V
IN
–
O
P
⎞
⎟
⎠
nmos_loss
www.aosmd.com
) Θ
×
Several layout tips are listed below for the best electric
and thermal performance:
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 not
4. Make the current trace from LX pins to L to Co to the
5. Pour copper plane on all unused board area and
6. Keep sensitive signal trace away from switching
JA
the PGND pin. Pour a maximized copper area to
the PGND pin and the VIN pin to help thermal
dissipation.
and the PGND pin as close as possible.
used, separate PGND from AGND and connect them
only at one point to avoid the PGND pin noise
coupling to the AGND pin.
PGND as short as possible.
connect it to stable DC nodes, like V
SGND.
node, LX. The copper pour area connected to the
LX pin should be as wide as possible to avoid the
switching noise on the LX pin coupling to other part
of circuit.
+
T
amb
IN
AOZ1025D
, PGND or
Page 11 of 15
IN
IN
and
pin