Datasheet
P =(V V )I-
D IN OUT OUT
TPS7A4001
SBVS162A –MARCH 2011– REVISED MARCH 2011
www.ti.com
LAYOUT
PACKAGE MOUNTING
Any tendency to activate the thermal protection circuit
Solder pad footprint recommendations for the indicates excessive power dissipation or an
TPS7A4001 are available at the end of this product inadequate heatsink. For reliable operation, junction
data sheet and at www.ti.com. temperature should be limited to a maximum of
+125°C. To estimate the margin of safety in a
complete design (including heatsink), increase the
BOARD LAYOUT RECOMMENDATIONS TO
ambient temperature until the thermal protection is
IMPROVE PSRR AND NOISE PERFORMANCE
triggered; use worst-case loads and signal conditions.
To improve ac performance such as PSRR, output
For good reliability, thermal protection should trigger
noise, and transient response, it is recommended that
at least +35°C above the maximum expected ambient
the board be designed with separate ground planes
condition of the particular application. This
for IN and OUT, with each ground plane connected
configuration produces a worst-case junction
only at the GND pin of the device. In addition, the
temperature of +125°C at the highest expected
ground connection for the output capacitor should
ambient temperature and worst-case load.
connect directly to the GND pin of the device.
The internal protection circuitry of the TPS7A4001
Equivalent series inductance (ESL) and ESR must be
has been designed to protect against overload
minimized in order to maximize performance and
conditions. It was not intended to replace proper
ensure stability. Every capacitor (C
IN
, C
OUT
, C
BYP
)
heatsinking. Continuously running the TPS7A4001
must be placed as close as possible to the device
into thermal shutdown degrades device reliability.
and on the same side of the PCB as the regulator
itself.
POWER DISSIPATION
Do not place any of the capacitors on the opposite
The ability to remove heat from the die is different for
side of the PCB from where the regulator is installed.
each package type, presenting different
The use of vias and long traces is strongly
considerations in the PCB layout. The PCB area
discouraged because they may impact system
around the device that is free of other components
performance negatively and even cause instability.
moves the heat from the device to the ambient air.
Performance data for JEDEC low- and high-K boards
If possible, and to ensure the maximum performance
are given in the Dissipation Ratings Table. Using
denoted in this product data sheet, use the same
heavier copper increases the effectiveness in
layout pattern used for TPS7A40 evaluation board,
removing heat from the device. The addition of plated
available at www.ti.com.
through-holes to heat dissipating layers also improves
the heatsink effectiveness.
THERMAL PROTECTION
Power dissipation depends on input voltage and load
Thermal protection disables the output when the
conditions. Power dissipation (P
D
) is equal to the
junction temperature rises to approximately +170°C,
product of the output current times the voltage drop
allowing the device to cool. When the junction
across the output pass element, as shown in
temperature cools to approximately +150°C, the
Equation 2:
output circuitry is enabled. Depending on power
dissipation, thermal resistance, and ambient
(2)
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.
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