TPS74201 datasheet(21/34 Pages) TI1

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TPS74201

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SBVS064M – DECEMBER 2005 – REVISED OCTOBER 2015

Thermal Protection (continued)

Activation of the thermal protection circuit indicates excessive power dissipation or inadequate heatsinking. For

reliable operation, junction temperature should be limited to 125°C maximum. To estimate the margin of safety in

a complete design (including heatsink), increase the ambient temperature until thermal protection is triggered;

use worst-case loads and signal conditions. For good reliability, thermal protection should trigger at least 40°C

above the maximum expected ambient condition of the application. This condition produces a worst-case junction

temperature of 125°C at the highest expected ambient temperature and worst-case load.

The internal protection circuitry of the TPS742 devices is designed to protect against overload conditions. It is not

intended to replace proper heatsinking. Continuously running the TPS742 devices into thermal shutdown

degrades device reliability.

10.4 Thermal Considerations

Using the thermal metrics

ΨJT and ΨJB, shown in Thermal Information, the junction temperature can be

estimated with corresponding formulas (given in Equation 6). For backwards compatibility, an older θJC,Top

parameter is listed as well.

where

•

PD is the power dissipation given by PD = (VIN – VOUT) × IOUT

•

TT is the temperature at the center-top of the IC package

•

TB is the PCB temperature measured 1mm away from the IC package on the PCB surface (as Figure 33

shows).

(6)

NOTE

Both TT and TB can be measured on actual application boards using a thermo-gun (an

infrared thermometer).

For more information about measuring TT and TB, see the application note Using New Thermal Metrics

(SBVA025), available for download at www.ti.com.

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