TPS734XX_16 Datasheet, PDF (10/20 Pages) Texas Instruments – 250mA, Low Quiescent Current, Ultra-Low Noise, High PSRR Low-Dropout Linear Regulator

TPS734xx
SBVS089F – DECEMBER 2007 – REVISED FEBRUARY 2009 ........................................................................................................................................ www.ti.com
Thermal Information
Thermal Protection
Thermal protection disables the output when the
junction temperature rises to approximately +165°C,
allowing the device to cool. When the junction
temperature cools to approximately +145°C the
output circuitry is again enabled. Depending on power
dissipation, thermal resistance, and ambient
temperature, the thermal protection circuit may cycle
on and off. 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 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.
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 depends on input voltage and load
conditions. Power dissipation is equal to the product
of the output current time the voltage drop across the
output pass element, as shown in Equation 2:
P_D + ^ǒV_IN*V ^Ǔ _OUT @ I_OUT
(2)
Package Mounting
Solder pad footprint recommendations for the
TPS734xx are available from the Texas Instruments
web site at www.ti.com.
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