Datasheet

Y Y
JT J T JT D
:T =T + P·
Y Y
JB J B JB D
:T =T + P·
T on PCB
B
T on of ICtop
T
1mm
(a) Example RGW (QFN) Package Measurement
(b) Example KTW (DDPAK) Package Measurement
1mm
T on of IC
T
top
(1)
T on PCB
surface
B
(2)
TPS743xx
www.ti.com SBVS065K –DECEMBER 2005–REVISED AUGUST 2010
ESTIMATING JUNCTION TEMPERATURE Where P
D
is the power dissipation shown by
Equation 1, T
T
is the temperature at the center-top of
Using the thermal metrics Ψ
JT
and Ψ
JB
, shown in the
the IC package, and T
B
is the PCB temperature
Thermal Information table, the junction temperature
measured 1mm away from the IC package on the
can be estimated with corresponding formulas (given
PCB surface (as Figure 34 shows).
in Equation 3). For backwards compatibility, an older
q
JC
,Top parameter is listed as well. NOTE: Both T
T
and T
B
can be measured on actual
application boards using a thermo-gun (an infrared
thermometer).
For more information about measuring T
T
and T
B
, see
the application note Using New Thermal Metrics
(3)
(SBVA025), available for download at www.ti.com.
(1) T
T
is measured at the center of both the X- and Y-dimensional axes.
(2) T
B
is measured below the package lead on the PCB surface.
Figure 34. Measuring Points for T
T
and T
B
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