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TPS720

SBVS100E – JUNE 2008 – REVISED SEPTEMBER 2015

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Thermal Considerations (continued)

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 maximum. 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. For good reliability, thermal protection should

trigger at least 35°C above the maximum expected ambient condition of the particular application. This

configuration 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 TPS720 has been designed to protect against overload conditions. It was

not intended to replace proper heatsinking. Continuously running the TPS720 into thermal shutdown degrades

device reliability.

10.4 Power Dissipation

The ability to remove heat from the die is different for each package type, presenting different considerations in

the printed-circuit-board (PCB) layout. The PCB area around the device that is free of other components moves

the heat from the device to the 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 the heatsink effectiveness.

Power dissipation depends on input voltage and load conditions. Power dissipation (PD) is equal to the product of

the output current times the voltage drop across the output pass element (VIN to VOUT), as shown in Equation 2:

PD = (VIN – VOUT) × IOUT

(2)