Datasheet

Thermal Information
Thermal Protection Power Dissipation
P
D
+
ǒ
V
IN
*V
OUT
Ǔ
@ I
OUT
(2)
Package Mounting
TPS734xx
SBVS089F – DECEMBER 2007 – REVISED FEBRUARY 2009 ........................................................................................................................................ www.ti.com
Thermal protection disables the output when the The ability to remove heat from the die is different for
junction temperature rises to approximately +165 ° C, each package type, presenting different
allowing the device to cool. When the junction considerations in the PCB layout. The PCB area
temperature cools to approximately +145 ° C the around the device that is free of other components
output circuitry is again enabled. Depending on power moves the heat from the device to the ambient air.
dissipation, thermal resistance, and ambient Performance data for JEDEC low- and high-K boards
temperature, the thermal protection circuit may cycle are given in the Dissipation Ratings table. Using
on and off. This cycling limits the dissipation of the heavier copper increases the effectiveness in
regulator, protecting it from damage as a result of removing heat from the device. The addition of plated
overheating. through-holes to heat-dissipating layers also
improves the heatsink effectiveness.
Any tendency to activate the thermal protection circuit
indicates excessive power dissipation or an Power dissipation depends on input voltage and load
inadequate heatsink. For reliable operation, junction conditions. Power dissipation is equal to the product
temperature should be limited to +125 ° C maximum. of the output current time the voltage drop across the
To estimate the margin of safety in a complete design output pass element, as shown in Equation 2 :
(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
Solder pad footprint recommendations for the
condition of your particular application. This
TPS734xx are available from the Texas Instruments
configuration produces a worst-case junction
web site at www.ti.com .
temperature of +125 ° C at the highest expected
ambient temperature and worst-case load.
The internal protection circuitry of the TPS734xx has
been designed to protect against overload conditions.
It was not intended to replace proper heatsinking.
Continuously running the TPS734xx into thermal
shutdown degrades device reliability.
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