Datasheet
P =(V V )I-
D IN OUT OUT
TLV1171
www.ti.com
SBVS177 –APRIL 2012
DROPOUT VOLTAGE
The TLV1171 uses a PMOS pass transistor to achieve low dropout. When (V
IN
– V
OUT
) is less than the dropout
voltage (V
DO
), the PMOS pass device is in the linear region of operation and the input-to-output resistance is the
R
DS(ON)
of the PMOS pass element. V
DO
scales approximately with output current because the PMOS device
behaves like a resistor in dropout.
As with any linear regulator, PSRR and transient response are degraded as (V
IN
– V
OUT
) approaches dropout.
TRANSIENT RESPONSE
As with any regulator, increasing the size of the output capacitor reduces over- and undershoot magnitude.
UNDERVOLTAGE LOCKOUT (UVLO)
The TLV1171 uses an undervoltage lockout circuit to keep the output shut off until the internal circuitry operates
properly.
THERMAL INFORMATION
Thermal protection disables the output when the junction temperature rises to approximately +165°C, thus
allowing the device to cool. When the junction temperature cools to approximately +145°C, the output circuitry is
again enabled. Depending on power dissipation, thermal resistance, and ambient temperature, the thermal
protection circuit may cycle on and off. This cycling limits 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 +125°C (max). 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.
The TLV1171 internal protection circuitry has been designed to protect against overload conditions. It is not
intended to replace proper heatsinking. Continuously running the TLV1171 into thermal shutdown degrades
device reliability.
POWER DISSIPATION
The ability to remove heat from the die is different for each package type and presents different considerations in
the printed circuit board (PCB) layout. The PCB area around the device that is free of other components moves
heat from the device to ambient air. Performance data for JEDEC low and high-K boards are given in the
Thermal Information 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 heatsink effectiveness.
Power dissipation depends on input voltage and load conditions. Power dissipation (P
D
) is equal to the product of
the output current and voltage drop across the output pass element, as shown in Equation 2:
(2)
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