P =(V

V

)I

-

D

IN

OUT

OUT

TLV1171

www.ti.com

SBVS177 – APRIL 2012

DROPOUT VOLTAGE

behaves like a resistor in 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.

the output current and voltage drop across the output pass element, as shown in Equation 2:

(2)

Copyright © 2012, Texas Instruments Incorporated

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