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TPS78225-Q1, TPS78227-Q1

TPS78228-Q1, TPS78230-Q1

www.ti.com

SBVS138 – DECEMBER 2009

THERMAL INFORMATION

THERMAL PROTECTION

Thermal protection disables the device output when the junction temperature rises to approximately 160°C,

allowing the device to cool. Once the junction temperature cools to approximately 140°C, the output circuitry is

enabled. Depending on power dissipation, thermal resistance, and ambient temperature, the thermal protection

circuit may cycle on and off again. This cycling limits the dissipation of the regulator, protecting it from damage

as a result of overheating.

Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate

heatsink. For reliable operation, junction temperature should be limited to 125°C maximum. To estimate the

margin of safety in a complete design (including heatsink), increase the ambient temperature until the thermal

protection is triggered; use worst-case loads and signal conditions. For good reliability, thermal protection should

trigger at least 35°C above the maximum expected ambient condition of your particular application. This

configuration produces a worst-case junction temperature of 125°C at the highest expected ambient temperature

and worst-case load.

The internal protection circuitry of the TPS782xx series has been designed to protect against overload

conditions. However, it is not intended to replace proper heatsinking. Continuously running the TPS782xx series

into thermal shutdown degrades device reliability.

POWER DISSIPATION

The ability to remove heat from the die is different for each package type, presenting different considerations in

the PCB layout. The PCB area around the device that is free of other components moves the heat from the

device to the ambient air. Performance data for JEDEC low- and high-K boards are given in the Dissipation

Ratings table. Using heavier copper increases the effectiveness in removing heat from the device. The addition

of plated through-holes to heat-dissipating layers also improves the heatsink effectiveness. Power dissipation

(2)

PACKAGE MOUNTING

Solder pad footprint recommendations for the TPS782xx series are available from the Texas Instruments web

site at www.ti.com through the TPS782xx series product folders.

Copyright © 2009, Texas Instruments Incorporated

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Product Folder Link(s): TPS78225-Q1 TPS78227-Q1 TPS78228-Q1 TPS78230-Q1