Datasheet

P =(V V )I-
D IN OUT OUT
TPS7A3001-EP
SBVS174 –OCTOBER 2011 www.ti.com
LAYOUT
PACKAGE MOUNTING
Solder pad footprint recommendations for the TPS7A3001 are available at the end of this product datasheet 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 equivalent series resistance (ESR) must be minimized in order to
maximize performance and ensure stability. Every capacitor (C
IN
, C
OUT
, C
NR/SS
, C
BYP
) must be placed as close as
possible to the device and on the same side of the printed circuit board (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 datasheet, use the same layout
pattern used for TPS7A30 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 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 TPS7A3001 has been designed to protect against overload conditions. It
was not intended to replace proper heatsinking. Continuously running the TPS7A3001 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. 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)
SUGGESTED LAYOUT AND SCHEMATIC
Layout is a critical part of good power-supply design. There are several signal paths that conduct fast-changing
currents or voltages that can interact with stray inductance or parasitic capacitance to generate noise or degrade
the power-supply performance. To help eliminate these problems, the IN pin should be bypassed to ground with
a low ESR ceramic bypass capacitor with a X5R or X7R dielectric.
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