Datasheet

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dVńdt +
V
OUT
C
OUT
80kW ø
(
R
1
) R
2
)
ø R
LOAD
(5)
REVERSE CURRENT
POWER DISSIPATION
THERMAL PROTECTION
Package Mounting
TPS73101-EP , , TPS73115-EP
TPS731125-EP , TPS73118-EP , TPS73125-EP , TPS73130-EP
TPS73132-EP , TPS73133-EP , TPS73150-EP
SGLS347A – JUNE 2006 – REVISED SEPTEMBER 2007
(Adjustable voltage version) 35 ° C above the maximum expected ambient
condition of your application. This 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 TPS731xx has
The NMOS pass element of the TPS731xx provides
been designed to protect against overload conditions.
inherent protection against current flow from the
It was not intended to replace proper heatsinking.
output of the regulator to the input when the gate of
Continuously running the TPS731xx into thermal
the pass device is pulled low. To ensure that all
shutdown will degrade device reliability.
charge is removed from the gate of the pass element,
the enable pin must be driven low before the input
voltage is removed. If this is not done, the pass
The ability to remove heat from the die is different for
element may be left on due to stored charge on the
each package type, presenting different
gate.
considerations in the PCB layout. The PCB area
After the enable pin is driven low, no bias voltage is
around the device that is free of other components
needed on any pin for reverse current blocking. Note
moves the heat from the device to the ambient air.
that reverse current is specified as the current flowing
Performance data for JEDEC low-K and high-K
out of the IN pin due to voltage applied on the OUT
boards are shown in the Power Dissipation Ratings
pin. There is additional current flowing into the OUT
table. Using heavier copper increases the
pin due to the 80-k Ω internal resistor divider to
effectiveness in removing heat from the device. The
ground (see Figure 2 and Figure 3 ).
addition of plated through-holes to heat-dissipating
layers also improves the heatsink effectiveness.
For the TPS73101, reverse current may flow when
V
FB
is more than 1 V above V
IN
.
Power dissipation depends on input voltage and load
conditions. Power dissipation is equal to the product
of the output current times the voltage drop across
the output pass element (V
IN
to V
OUT
):
Thermal protection disables the output when the
P
D
= (V
IN
– V
OUT
) × I
OUT
junction temperature rises to approximately 160 ° C,
allowing the device to cool. When the junction
Power dissipation can be minimized by using the
temperature cools to approximately 140 ° C, the output
lowest possible input voltage necessary to ensure the
circuitry is again enabled. Depending on power
required output voltage.
dissipation, thermal resistance, and ambient
temperature, the thermal protection circuit may cycle
on and off. This limits the dissipation of the regulator,
protecting it from damage due to overheating. Solder pad footprint recommendations for the
TPS731xx are presented in Application Bulletin
Any tendency to activate the thermal protection circuit
Solder Pad Recommendations for Surface-Mount
indicates excessive power dissipation or an
Devices (AB-132), available from the Texas
inadequate heatsink. For reliable operation, junction
Instruments web site at www.ti.com.
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
Copyright © 2006 – 2007, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Link(s): TPS73101-EP TPS73115-EP TPS731125-EP TPS73118-EP TPS73125-EP TPS73130-EP
TPS73132-EP TPS73133-EP TPS73150-EP