TPS51200-EP_17 Datasheet, PDF (27/35 Pages) Texas Instruments – Sink and Source DDR Termination Regulator

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Thermal Design Considerations (continued)
Maximum power dissipation allowed by the package is calculated by Equation 6.
P_PKG
=
T_J(max) - T_A(max)
q_JA
where
•
•
•
T_J(max) is 125°C.
T_A(max) is the maximum ambient temperature in the system.
θ_JA is the thermal resistance from junction to ambient.
TPS51200-EP
SLUSA48 – JUNE 2016
(6)
NOTE
Because Equation 6 demonstrates the effects of heat spreading in the ground plane, use it
as a guideline only. Do not use Equation 6 to estimate actual thermal performance in real
application environments.
In an application where the device is mounted on PCB, TI strongly recommends using ψ_JT and ψ_JB, as explained
in the section pertaining to estimating junction temperature in the Semiconductor and IC Package Thermal
Metrics application report, SPRA953. Using the thermal metrics ψ_JT and ψ_JB, as shown in the Thermal
Information table, estimate the junction temperature with corresponding formulas shown in Equation 7. The older
θ_JC top parameter specification is listed as well for the convenience of backward compatibility.
T_J = T_T + Y_JT ´ P_D
(7)
T_J = T_B + Y_JB ´ P_D
where
• P_D is the power dissipation shown in Equation 4 and Equation 5.
• T_T is the temperature at the center-top of the IC package.
• T_B is the PCB temperature measured 1-mm away from the thermal pad package on the PCB surface (see
Figure 32).
(8)
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 report Using New Thermal Metrics (SBVA025).
.
Land Pad
3 mm x 1.9 mm
T_T on top of package
T_B on PCB surface
Exposed Thermal
Die Pad,
2.48 mm x 1.74 mm
UDG-08018
1 mm
Figure 31. Recommended Land Pad Pattern
Figure 32. Package Thermal Measurement
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