Datasheet

P =(V V ) I- ´
D IN OUT OUT
TI Information — Selective Disclosure
TPS780 Series
www.ti.com SBVS083D –JANUARY 2007–REVISED SEPTEMBER 2012
THERMAL INFORMATION
The internal protection circuitry of the TPS780 series
THERMAL PROTECTION
has been designed to protect against overload
conditions. However, it is not intended to replace
Thermal protection disables the output when the
proper heatsinking. Continuously running the TPS780
junction temperature rises to approximately +160°C,
series into thermal shutdown degrades device
allowing the device to cool. Once the junction
reliability.
temperature cools to approximately +140°C, the
output circuitry is enabled. Depending on power
dissipation, thermal resistance, and ambient POWER DISSIPATION
temperature, the thermal protection circuit may cycle
The ability to remove heat from the die is different for
on and off again. This cycling limits the dissipation of
each package type, presenting different
the regulator, protecting it from damage as a result of
considerations in the PCB layout. The PCB area
overheating.
around the device that is free of other components
Any tendency to activate the thermal protection circuit moves the heat from the device to the ambient air.
indicates excessive power dissipation or an Performance data for JEDEC low- and high-K boards
inadequate heatsink. For reliable operation, junction are given in the Dissipation Ratings table. Using
temperature should be limited to +125°C maximum. heavier copper increases the effectiveness in
To estimate the margin of safety in a complete design removing heat from the device. The addition of plated
(including heatsink), increase the ambient through-holes to heat-dissipating layers also
temperature until the thermal protection is triggered; improves the heatsink effectiveness. Power
use worst-case loads and signal conditions. For good dissipation depends on input voltage and load
reliability, thermal protection should trigger at least conditions. Power dissipation (P
D
) is equal to the
+35°C above the maximum expected ambient product of the output current times the voltage drop
condition of your particular application. This across the output pass element (V
IN
to V
OUT
), as
configuration produces a worst-case junction shown in Equation 4:
temperature of +125°C at the highest expected
(4)
ambient temperature and worst-case load.
PACKAGE MOUNTING
Solder pad footprint recommendations for the
TPS780 series are available from the Texas
Instruments web site at www.ti.com through the
TPS780 series product folders.
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