General PowerPAD
t
Design Considerations
1-18
General Information
6) The top-side solder mask should leave exposed the terminals of the
package and the thermal pad area with its holes. Any larger holes outside
the thermal pad area, but still under the package, should be covered with
solder mask.
7) Apply solder paste to the exposed thermal pad area and all of the
operational amplifier terminals.
8) With these preparatory steps in place, the THS7002 is simply placed in
position and run through the solder reflow operation as any standard
surface-mount component. This results in a part that is properly installed.
The actual thermal performance achieved with the THS7002 in its PowerPAD
package depends on the application. In the example above, if the size of the
internal ground plane is approximately 3 inches
×
3 inches, then the expected
thermal coefficient,
θ
JA
,
is
about 27.8
_
C/W. For a given
θ
JA
, the maximum
power dissipation is shown in Figure 1–13 and is calculated by the following
formula:
P
D
+
ǒ
T
MAX
–T
A
q
JA
Ǔ
Where:
P
D
= Maximum power dissipation of THS7002 (watts)
T
MAX
= Absolute maximum junction temperature (150
°
C)
T
A
= Free-ambient air temperature (
°
C)
θ
JA
=
θ
JC +
θ
CA
θ
JC
= Thermal coefficient from die junction to case (0.72
°
C/W)
θ
CA
= Thermal coefficient from case to ambient air (
°
C/W)
Figure 1–13. Maximum Power Dissipation vs. Free-Air Temperature
TA – Free-Air Temperature –
°
C
–40
–20
0
20
80
100
60
40
MAXIMUM POWER DISSIPATION
vs
FREE-AIR TEMPERATURE
5
3
1
0
4
2
6
7
Maximum Power Dissipation – W
8
9
Tj = 150
°
C
PCB Size = 3” x 3”
No Air Flow
θ
JA = 27.9
°
C/W
2 oz Trace and
Copper Pad
with Solder
θ
JA = 56.2
°
C/W
2 oz Trace and Copper Pad
without Solder