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TPS72615DCQ Datasheet(PDF) 9 Page - Texas Instruments |
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TPS72615DCQ Datasheet(HTML) 9 Page - Texas Instruments |
9 / 23 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 TPS726126 TPS72615, TPS72616 TPS72618, TPS72625 www.ti.com SLVS403H – MAY 2002 – REVISED JUNE 2010 In general, the maximum expected power (PD(max)) consumed by a linear regulator is computed as: (1) Where: • VI(avg) is the average input voltage. • VO(avg) is the average output voltage. • O(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 ®qJC), the case to heatsink ®qCS), and the heatsink to ambient ®qSA). 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 19 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 19. Thermal Resistances Equation 2 summarizes the computation: (2) 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. Even if no external black body radiator type heatsink is attached to the package, the board on which the regulator is mounted provides some heatsinking through the pin solder connections. Some packages, like the DDPAK and SOT223 packages, use a copper plane underneath the package or the circuit board's ground plane for additional heatsinking to improve their thermal performance. Computer-aided thermal modeling can be used to compute very accurate approximations of an integrated circuit's thermal performance in different operating environments (e.g., different types of circuit boards, different types and sizes of heatsinks, and different air flows, etc.). Using these models, the three thermal resistances can be combined into one thermal resistance between junction and ambient ®qJA). This RqJAis valid only for the specific operating environment used in the computer model. Copyright © 2002–2010, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Link(s): TPS726126 TPS72615 TPS72616 TPS72618 TPS72625 |
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