Datasheet

1mm
T on PCB
B
T on top
of IC surface
T
1mm
T
B
T
T
20
18
16
14
12
10
8
6
4
2
0
Y Yand ( C/W)
JT JB
°
0 2
4
6 8 10
BoardCopperArea(in )
2
51 3 7 9
Y
JT
Y
JB
Y Y
JT J T JT D
:T =T + P·
Y Y
JB J B JB D
:T =T + P·
TPS7A80xx
SBVS135H –JUNE 2010–REVISED JANUARY 2013 www.ti.com
NOTE: When the device is mounted on an By looking at Figure 34, the new thermal metrics (Ψ
JT
application PCB, it is strongly recommended to use and Ψ
JB
) have very little dependency on board size.
Ψ
JT
and Ψ
JB
, as explained in the Estimating Junction That is, using Ψ
JT
or Ψ
JB
with Equation 6 is a good
Temperature section. way to estimate T
J
by simply measuring T
T
or T
B
,
regardless of the application board size.
ESTIMATING JUNCTION TEMPERATURE
Using the thermal metrics Ψ
JT
and Ψ
JB
, as shown in
the Thermal Information table, the junction
temperature can be estimated with corresponding
formulas (given in Equation 6). For backwards
compatibility, an older θ
JC
,Top parameter is listed as
well.
(6)
Where P
D
is the power dissipation shown by
Equation 5, T
T
is the temperature at the center-top of
the IC package, and T
B
is the PCB temperature
measured 1mm away from the IC package on the
PCB surface (as Figure 35 shows).
Figure 34. Ψ
JT
and Ψ
JB
vs Board Size
NOTE: Both T
T
and T
B
can be measured on actual
application boards using a thermo-gun (an infrared
thermometer).
For a more detailed discussion of why TI does not
recommend using θ
JC(top)
to determine thermal
For more information about measuring T
T
and T
B
, see
characteristics, refer to application report SBVA025,
the application note SBVA025, Using New Thermal
Using New Thermal Metrics, available for download
Metrics, available for download at www.ti.com.
at www.ti.com. For further information, refer to
application report SPRA953, IC Package Thermal
Metrics, also available on the TI website.
Figure 35. Measuring Points for T
T
and T
B
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