Datasheet

P =(V V ) I- ´
D IN OUT OUT
TLV700xx
www.ti.com SLVSA00D –SEPTEMBER 2009–REVISED NOVEMBER 2012
Dropout Voltage For good reliability, thermal protection should trigger
at least +35°C above the maximum expected ambient
The TLV700xx uses a PMOS pass transistor to
condition of the particular application. This
achieve low dropout. When (V
IN
– V
OUT
) is less than
configuration produces a worst-case junction
the dropout voltage (V
DO)
, the PMOS pass device is
temperature of +125°C at the highest expected
in the linear region of operation and the input-to-
ambient temperature and worst-case load.
output resistance is the R
DS(ON)
of the PMOS pass
element. V
DO
scales approximately with output The internal protection circuitry of the TLV700xx has
current because the PMOS device behaves as a been designed to protect against overload conditions.
resistor in dropout. It was not intended to replace proper heatsinking.
Continuously running the TLV700xx into thermal
As with any linear regulator, PSRR and transient
shutdown degrades device reliability.
response are degraded as (V
IN
– V
OUT
) approaches
dropout. This effect is shown in Figure 13 in the
Power Dissipation
Typical Characteristics section.
The ability to remove heat from the die is different for
Transient Response each package type, presenting different
considerations in the printed circuit board (PCB)
As with any regulator, increasing the size of the
layout. The PCB area around the device that is free
output capacitor reduces over-/undershoot magnitude
of other components moves the heat from the device
but increases the duration of the transient response.
to the ambient air. Performance data for JEDEC low
and high-K boards are given in the Dissipation
Undervoltage Lockout (UVLO)
Ratings table. Using heavier copper increases the
effectiveness in removing heat from the device. The
The TLV700xx uses an undervoltage lockout circuit to
addition of plated through-holes to heat-dissipating
keep the output shut off until internal circuitry is
layers also improves heatsink effectiveness.
operating properly.
Power dissipation depends on input voltage and load
Thermal Information
conditions. Power dissipation (PD) is equal to the
product of the output current and the voltage drop
Thermal protection disables the output when the
across the output pass element, as shown in
junction temperature rises to approximately +160°C,
Equation 1.
allowing the device to cool. When the junction
temperature cools to approximately +140°C, the
(1)
output circuitry is again enabled. Depending on power
dissipation, thermal resistance, and ambient
Package Mounting
temperature, the thermal protection circuit may cycle
Solder pad footprint recommendations for the
on and off. This cycling limits the dissipation of the
TLV700xx are available from the Texas Instruments
regulator, protecting it from damage as a result of
web site at www.ti.com. The recommended land
overheating.
patterns for the DSE, DDC, and DCK packages are
Any tendency to activate the thermal protection circuit
shown in Figure 22, Figure 23, and Figure 24,
indicates excessive power dissipation or an
respectively. Figure 25, Figure 26, and Figure 27
inadequate heatsink. For reliable operation, junction
show the mechanical package dimensions for the
temperature should be limited to +125°C maximum.
DSE, DDC, and DCK packages, respectively.
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.
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