Datasheet

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)
Y Y
JT J T JT D
:T =T + P·
Y Y
JB J B JB D
:T =T + P·
TPS744xx
SBVS066O –DECEMBER 2005–REVISED MARCH 2013 www.ti.com
NOTE: When the device is mounted on an
application PCB, it is strongly recommended to use
(6)
Ψ
JT
and Ψ
JB
, as explained in the Estimating Junction
Temperature section.
Where P
D
is the power dissipation shown by
Equation 4, T
T
is the temperature at the center-top of
ESTIMATING JUNCTION TEMPERATURE
the IC package, and T
B
is the PCB temperature
measured 1mm away from the IC package on the
Using the thermal metrics Ψ
JT
and Ψ
JB
, shown in the
PCB surface (as Figure 36 shows).
Thermal Information table, the junction temperature
can be estimated with corresponding formulas (given
NOTE: Both T
T
and T
B
can be measured on actual
in Equation 6). For backwards compatibility, an older
application boards using a thermo-gun (an infrared
θ
JC
,Top parameter is listed as well.
thermometer).
For more information about measuring T
T
and T
B
, see
the application note Using New Thermal Metrics
(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 36. Measuring Points for T
T
and T
B
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