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TB5R3LD Datasheet(PDF) 8 Page - Texas Instruments |
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TB5R3LD Datasheet(HTML) 8 Page - Texas Instruments |
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8 / 15 page  www.ti.com APPLICATION INFORMATION Power Dissipation V Sn I Sn (1) (V Ln I Ln) (2) T J + TA ) PD q JA (3) T J + TA ) PD q JA(S) (4) q JA(S) + q JC )qCA q JB )qBA q JC )qCA)qJB)qBA (5) 40 60 80 100 120 140 0 100 200 300 400 500 D, Low−K DW, Low−K DW, High−K D, High−K TB5R3 SLLS643A – SEPTEMBER 2005 – REVISED OCTOBER 2007 which the device is mounted and on the airflow over the device and PCB. JEDEC/EIA has defined standardized test conditions for measuring θ JA. Two The power dissipation rating, often listed as the commonly used conditions are the low-K and the package dissipation rating, is a function of the high-K boards, covered by EIA/JESD51-3 and ambient temperature, TA, and the airflow around the EIA/JESD51-7 respectively. Figure 10 shows the device. This rating correlates with the device's low-K and high-K values of θ JA versus air flow for this maximum junction temperature, sometimes listed in device and its package options. the absolute maximum ratings tables. The maximum The standardized θ JA values may not accurately junction temperature accounts for the processes and represent the conditions under which the device is materials used to fabricate and package the device, used. This can be due to adjacent devices acting as in addition to the desired life expectancy. heat sources or heat sinks, to nonuniform airflow, or There are two common approaches to estimating the to the system PCB having significantly different internal die junction temperature, TJ. In both of these thermal characteristics than the standardized test methods, the device internal power dissipation PD PCBs. The second method of system thermal needs to be calculated This is done by totaling the analysis is more accurate. This calculation uses the supply power(s) to arrive at the system power power dissipation and ambient temperature, along dissipation: with two device and two system-level parameters: • θ JC, the junction-to-case thermal resistance, in degrees Celsius per watt and then subtracting the total power dissipation of the • θ JB, the junction-to-board thermal resistance, in external load(s): degrees Celsius per watt • θ CA, the case-to-ambient thermal resistance, in degrees Celsius per watt The first TJ calculation uses the power dissipation • θ BA, the board-to-ambient thermal resistance, in and ambient temperature, along with one parameter: degrees Celsius per watt. θ JA, the junction-to-ambient thermal resistance, in In this analysis, there are two parallel paths, one degrees Celsius per watt. through the case (package) to the ambient, and The product of PD and θJA is the junction temperature another through the device to the PCB to the rise above the ambient temperature. Therefore: ambient. The system-level junction-to-ambient thermal impedance, θ JA(S), is the equivalent parallel impedance of the two parallel paths: where The device parameters θ JC and θJB account for the internal structure of the device. The system-level parameters θ CA and θBA take into account details of the PCB construction, adjacent electrical and mechanical components, and the environmental conditions including airflow. Finite element (FE), finite difference (FD), or computational fluid dynamics (CFD) programs can determine θ CA and θBA. Details on using these programs are beyond the scope of this data sheet, but are available from the software manufacturers. Figure 10. Thermal Impedance vs Air Flow Note that θ JA is highly dependent on the PCB on 8 Submit Documentation Feedback Copyright © 2005–2007, Texas Instruments Incorporated Product Folder Link(s): TB5R3 |
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