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TPS72518KTT Datasheet(PDF) 11 Page - Texas Instruments |
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TPS72518KTT Datasheet(HTML) 11 Page - Texas Instruments |
11 / 29 page P D max + VI(avg) * VO(avg) I O(avg) ) V I(avg) x I (Q) A B C TJ A RθJC TC B RθCS TA C RθSA (a) (b) DDPAK Package SOT223 Package CIRCUIT BOARD COPPER AREA B A C T J + T A ) P Dmax x R θJC ) RθCS ) RθSA TPS72501 TPS72515, TPS72516 TPS72518, TPS72525 www.ti.com SLVS341E – MAY 2002 – REVISED JUNE 2010 THERMAL INFORMATION The amount of heat that an LDO linear regulator generates is directly proportional to the amount of power it dissipates during operation. All integrated circuits have a maximum allowable junction temperature (TJmax) above which normal operation is not assured. A system designer must design the operating environment so that the operating junction temperature (TJ) does not exceed the maximum junction temperature (TJmax). The two main environmental variables that a designer can use to improve thermal performance are air flow and external heatsinks. The purpose of this information is to aid the designer in determining the proper operating environment for a linear regulator that is operating at a specific power level. In general, the maximum expected power (PD(max)) consumed by a linear regulator is computed as: (3) Where: • VI(avg) is the average input voltage. • VO(avg) is the average output voltage. • IO(avg) is the average output current. • I(Q) is the quiescent current. For most TI LDO regulators, the quiescent current is insignificant compared to the average output current; therefore, the term VI(avg) x I(Q) can be neglected. The operating junction temperature is computed by adding the ambient temperature (TA) and the increase in temperature due to the regulator's power dissipation. The temperature rise is computed by multiplying the maximum expected power dissipation by the sum of the thermal resistances between the junction and the case (RqJC), the case to heatsink (RqCS), and the heatsink to ambient (RqSA). Thermal resistances are measures of how effectively an object dissipates heat. Typically, the larger the device, the more surface area available for power dissipation and the lower the object's thermal resistance. Figure 20 illustrates these thermal resistances for (a) a SOT223 package mounted in a JEDEC low-K board, and (b) a DDPAK package mounted on a JEDEC high-K board. Figure 20. Thermal Resistances Equation 4 summarizes the computation: (4) The RqJC is specific to each regulator as determined by its package, lead frame, and die size provided in the regulator's data sheet. The RqSA is a function of the type and size of heatsink. For example, black body radiator type heatsinks can have RqCS values ranging from 5°C/W for very large heatsinks to 50°C/W for very small heatsinks. The RqCS is a function of how the package is attached to the heatsink. For example, if a thermal compound is used to attach a heatsink to a SOT223 package, RqCSof 1°C/W is reasonable. Copyright © 2002–2010, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): TPS72501 TPS72515 TPS72516 TPS72518 TPS72525 |
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