Datasheet

P =(V V )I-
D IN OUT OUT
TPS7A41
SBVS183 –DECEMBER 2011 www.ti.com
LAYOUT
PACKAGE MOUNTING
Solder pad footprint recommendations for the TPS7A4101 are available at the end of this product data sheet and
at www.ti.com.
BOARD LAYOUT RECOMMENDATIONS TO IMPROVE PSRR AND NOISE PERFORMANCE
To improve ac performance such as PSRR, output noise, and transient response, it is recommended that the
board be designed with separate ground planes for IN and OUT, with each ground plane connected only at the
GND pin of the device. In addition, the ground connection for the output capacitor should connect directly to the
GND pin of the device.
Equivalent series inductance (ESL) and ESR must be minimized in order to maximize performance and ensure
stability. Every capacitor (C
IN
, C
OUT
, C
BYP
) must be placed as close as possible to the device and on the same
side of the PCB as the regulator itself.
Do not place any of the capacitors on the opposite side of the PCB from where the regulator is installed. The use
of vias and long traces is strongly discouraged because they may impact system performance negatively and
even cause instability.
If possible, and to ensure the maximum performance denoted in this product data sheet, use the same layout
pattern used for TPS7A41 evaluation board, available at www.ti.com.
THERMAL PROTECTION
Thermal protection disables the output when the junction temperature rises to approximately +170°C, allowing
the device to cool. When the junction temperature cools to approximately +150°C, the output circuitry is 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 a maximum of +125°C. 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 the 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 TPS7A4101 has been designed to protect against overload conditions. It
was not intended to replace proper heatsinking. Continuously running the TPS7A4101 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 (P
D
) is equal to the product of
the output current times the voltage drop across the output pass element, as shown in Equation 2:
(2)
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