TPS780 datasheet(18/27 Pages) TI

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THERMAL INFORMATION

THERMAL PROTECTION

POWER DISSIPATION

P =(V

)

OUT

(4)

PACKAGE MOUNTING

TPS780 Series

SBVS083C – JANUARY 2007 – REVISED MAY 2008 ....................................................................................................................................................... www.ti.com

Thermal protection disables the output when the

The ability to remove heat from the die is different for

junction temperature rises to approximately +160

°C,

each

package

type,

presenting

different

allowing the device to cool. Once the junction

considerations in the PCB layout. The PCB area

temperature cools to approximately +140

°C, the

around the device that is free of other components

output circuitry is enabled. Depending on power

moves the heat from the device to the ambient air.

dissipation,

thermal

resistance,

and

ambient

Performance data for JEDEC low- and high-K boards

temperature, the thermal protection circuit may cycle

are given in the Dissipation Ratings table. Using

on and off again. This cycling limits the dissipation of

heavier

copper

increases

the

effectiveness

the regulator, protecting it from damage as a result of

removing heat from the device. The addition of plated

overheating.

through-holes

heat-dissipating

layers

also

improves

the

heatsink

effectiveness.

Power

Any tendency to activate the thermal protection circuit

dissipation depends on input voltage and load

indicates

excessive

power

dissipation

conditions. Power dissipation (PD) is equal to the

inadequate heatsink. For reliable operation, junction

product of the output current times the voltage drop

temperature should be limited to +125

°C maximum.

across the output pass element (VIN to VOUT), as

To estimate the margin of safety in a complete design

shown in Equation 4:

(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

+35

°C above the maximum expected ambient

Solder

pad

footprint

recommendations

for

the

condition

your

particular

application.

This

TPS780

series

are

available

from

the

Texas

configuration

produces

worst-case

junction

Instruments web site at www.ti.com through the

temperature of +125

°C at the highest expected

TPS780 series product folders.

ambient temperature and worst-case load.

The internal protection circuitry of the TPS780 series

has been designed to protect against overload

conditions. However, it is not intended to replace

proper heatsinking. Continuously running the TPS780

series

into

thermal

shutdown

degrades

device

reliability.

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