Datasheet
(a) Example DRB (SON) Package Measurement
(b) Example DRV (SON) Package Measurement
1mm
T on top
of IC
T
T on PCB
surface
B
T on top
of IC
T
T on PCB
surface
B
1mm
See note (1)
Y Y
JT J T JT D
:T =T + P·
Y Y
JB J B JB D
:T =T + P·
35
30
25
20
15
10
5
0
Y Yand ( C/W)
JT JB
°
0 2
4
6 8 10
Board Copper Area (in )
2
51 3 7 9
DRV
DRB
Y
JT
DRV
DRB
Y
JB
TPS735xx
www.ti.com
SBVS087K –JUNE 2008–REVISED AUGUST 2013
Figure 22 illustrates the variation of θ
JA
as a function By looking at Figure 23, the new thermal metrics (Ψ
JT
of ground plane copper area in the board. It is and Ψ
JB
) have very little dependency on board size.
intended only as a guideline to demonstrate the That is, using Ψ
JT
or Ψ
JB
with Equation 4 is a good
effects of heat spreading in the ground plane and way to estimate T
J
by simply measuring T
T
or T
B
,
should not be used to estimate actual thermal regardless of the application board size.
performance in real application environments.
NOTE: When the device is mounted on an
application PCB, it is strongly recommended to use
Ψ
JT
and Ψ
JB
, as explained in the Estimating Junction
Temperature section.
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 4). For backwards
compatibility, an older θ
JC
,Top parameter is listed as
well.
(4)
Figure 23. Ψ
JT
and Ψ
JB
vs Board Size
Where P
D
is the power dissipation shown by
Equation 2, T
T
is the temperature at the center-top of
For a more detailed discussion of why TI does not
the IC package, and T
B
is the PCB temperature
recommend using θ
JC(top)
to determine thermal
measured 1mm away from the IC package on the
characteristics, refer to application report SBVA025,
PCB surface (as Figure 24 shows).
Using New Thermal Metrics, available for download
at www.ti.com. For further information, refer to
NOTE: Both T
T
and T
B
can be measured on actual
application report SPRA953, IC Package Thermal
application boards using a thermo-gun (an infrared
Metrics, also available on the TI website.
thermometer).
For more information about measuring T
T
and T
B
, see
the application note SBVA025, Using New Thermal
Metrics, available for download at www.ti.com.
(1) Power dissipation may limit operating range. Check Thermal Information table.
Figure 24. Measuring Points for T
T
and T
B
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