TPS73701 datasheet(12/18 Pages) TI

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THERMAL PROTECTION

POWER DISSIPATION

+ VIN * VOUT

OUT

(5)

Package Mounting

TPS737xx

SBVS067C – JANUARY 2006 – REVISED AUGUST 2006

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. When 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 again enabled. Depending on

moves the heat from the device to the ambient air.

power dissipation, thermal resistance, and ambient

Performance data for JEDEC low- and high-K boards

temperature, the thermal protection circuit may cycle

are shown in the Power Dissipation Ratings table.

on and off. This cycling limits the dissipation of the

Using heavier copper will increase the effectiveness

regulator,

protecting

from

damage

due

in removing heat from the device. The addition of

overheating.

plated through-holes to heat-dissipating layers will

also improve the heatsink effectiveness.

Any tendency to activate the thermal protection

circuit indicates excessive power dissipation or an

Power dissipation depends on input voltage and load

inadequate heatsink. For reliable operation, junction

conditions. Power dissipation (PD) is equal to the

temperature should be limited to +125

°C maximum.

product of the output current times the voltage drop

To estimate the margin of safety in a complete

across the output pass element (VIN to VOUT):

design (including heatsink), increase the ambient

temperature until the thermal protection is triggered;

use worst-case loads and signal conditions. For good

Power dissipation can be minimized by using the

reliability, thermal protection should trigger at least

lowest possible input voltage necessary to assure

+35

°C above the maximum expected ambient

the required output voltage.

condition of your application. This produces a

worst-case junction temperature of +125

°C at the

highest

expected

ambient

temperature

and

Solder

pad

footprint

recommendations

for

the

worst-case load.

TPS737xx are presented in Application Bulletin

The internal protection circuitry of the TPS737xx has

Solder Pad Recommendations for Surface-Mount

been

designed

protect

against

overload

Devices

(SBFA015),

available

from

the

Texas

conditions. It was not intended to replace proper

Instruments web site at www.ti.com.

heatsinking. Continuously running the TPS737xx into

thermal shutdown will degrade device reliability.

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