TPS73701_13 Datasheet, PDF (16/31 Pages) Texas Instruments – 1A Low-Dropout Regulator with Reverse Current Protection

TPS737xx
SBVS067O – JANUARY 2006 – REVISED JUNE 2012
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 8). For backwards
compatibility, an older θ_JC,Top parameter is listed as
well.
Y_JT:
T
J
=
T
T
+
Y_JT
·
P
D
Y_JB:
T
J
=
T
B
+
Y_JB
·
P
D
(8)
Where P_D is the power dissipation shown by
Equation 6, 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).
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 SBVA025, Using New Thermal
Metrics, available for download at www.ti.com.
By looking at Figure 34, the new thermal metrics (Ψ_JT
and Ψ_JB) have very little dependency on board size.
That is, using Ψ_JT or Ψ_JB with Equation 8 is a good
way to estimate T_J by simply measuring T_T or T_B,
regardless of the application board size.
T_B on PCB
surface
1mm
T_T on top
of IC
T_B on PCB
surface
1mm
www.ti.com
35
30
DRV
25
DCQ Y_JB
DRB
20
15
DRV
DCQ Y_JT
10
DRB
5
0
0 1 2 3 4 5 6 7 8 9 10
Board Copper Area (in²)
Figure 34. Ψ_JT and Ψ_JB vs Board Size
For a more detailed discussion of why TI does not
recommend using θ_JC(top) to determine thermal
characteristics, refer to application report SBVA025,
Using New Thermal Metrics, available for download
at www.ti.com. For further information, refer to
application report SPRA953, IC Package Thermal
Metrics, also available on the TI website.
T_T on top
of IC
T_B
1mm X
T_T
X
See note (1)
(a) Example DRB (SON) Package Measurement
(b) Example DRV (SON) Package Measurement
(c) Example DCQ (SOT-223) Package Measurement
(1) Power dissipation may limit operating range. Check Thermal Information table.
Figure 35. Measuring Points for T_T and T_B
16
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