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TPS78625DCQG4 Datasheet(PDF) 10 Page - Texas Instruments |
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TPS78625DCQG4 Datasheet(HTML) 10 Page - Texas Instruments |
10 / 21 page www.ti.com THERMAL INFORMATION T J + TA ) PDmax R qJC ) R qCS ) R qSA (5) P D max + VIN(avg) * VOUT(avg) I OUT(avg) ) VIN(avg) 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 TPS786xx SLVS389G – SEPTEMBER 2002 – REVISED JULY 2006 increase in temperature due to the regulator power The amount of heat that an LDO linear regulator dissipation. The temperature rise is computed by generates is directly proportional to the amount of multiplying the maximum expected power dissipation power it dissipates during operation. All integrated by the sum of the thermal resistances between the circuits have a maximum allowable junction junction and the case (RθJC), the case to heatsink temperature (TJmax) above which normal operation (RθCS), and the heatsink to ambient (RθSA). Thermal is not assured. A system designer must design the resistances are measures of how effectively an operating environment so that the operating junction object dissipates heat. Typically, the larger the temperature (TJ) does not exceed the maximum device, the more surface area available for power junction temperature (TJmax). The two main dissipation and the lower the object's thermal environmental variables that a designer can use to resistance. improve thermal performance are air flow and external heatsinks. The purpose of this information is Figure 26 illustrates these thermal resistances for (a) to aid the designer in determining the proper a SOT223 package mounted in a JEDEC low-K operating environment for a linear regulator that is board, and (b) a DDPAK package mounted on a operating at a specific power level. JEDEC high-K board. In general, the maximum expected power (PDmax) Equation 5 summarizes the computation: consumed by a linear regulator is computed as shown in Equation 4: The RθJC is specific to each regulator as determined by its package, lead frame, and die size provided in (4) the regulator data sheet. The RθSA is a function of where: the type and size of heatsink. For example, black body radiator type heatsinks can have RθCS values • V IN(avg) is the average input voltage. ranging from 5 °C/W for very large heatsinks to • V OUT(avg) is the average output voltage. 50 °C/W for very small heatsinks. The Rθ CS is a • I OUT(avg) is the average output current. function of how the package is attached to the • I Q is the quiescent current. heatsink. For example, if a thermal compound is used to attach a heatsink to a SOT223 package, For most TI LDO regulators, the quiescent current is RθCS of 1°C/W is reasonable. insignificant compared to the average output current; therefore, the term VIN(avg)× IQ can be neglected. The operating junction temperature is computed by adding the ambient temperature (TA) and the Figure 26. Thermal Resistances 10 Submit Documentation Feedback |
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