LP2992_15 Datasheet, PDF (19/35 Pages) Texas Instruments – LP2992 Micropower 250-mA Low-Noise Ultralow-Dropout Regulator in SOT-23 and WSON Packages Designed for Use with Very Low-ESR Output Capacitors

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LP2992
SNVS171I – NOVEMBER 2001 – REVISED NOVEMBER 2015
8.2.2.5 Estimating Junction Temperature
The EIA/JEDEC standard recommends the use of psi (Ψ) thermal characteristics to estimate the junction
temperatures of surface mount devices on a typical PCB board application. These characteristics are not true
thermal resistance values, but rather package specific thermal characteristics that offer practical and relative
means of estimating junction temperatures. These psi metrics are determined to be significantly independent of
copper-spreading area. The key thermal characteristics (Ψ_JT and Ψ_JB) are given in Thermal Information and are
used in accordance with Equation 4 or Equation 5.
T_J(MAX) = T_TOP + (Ψ_JT × P_D(MAX))
where
• P_D(MAX) is explained in Equation 3
• T_TOP is the temperature measured at the center-top of the device package.
(4)
T_J(MAX) = T_BOARD + (Ψ_JB × P_D(MAX))
where
• P_D(MAX) is explained in Equation 3.
• T_BOARD is the PCB surface temperature measured 1-mm from the device package and centered on the
package edge.
(5)
For more information about the thermal characteristics Ψ_JT and Ψ_JB, see TI Application Report Semiconductor
and IC Package Thermal Metrics (SPRA953); for more information about measuring T_TOP and T_BOARD, see the TI
Application Report Using New Thermal Metrics (SBVA025); and for more information about the EIA/JEDEC
JESD51 PCB used for validating R_θJA, see the TI Application Report Thermal Characteristics of Linear and Logic
Packages Using JEDEC PCB Designs (SZZA017). These application notes are available at www.ti.com.
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