TPS737 datasheet(24/50 Pages) TI2

24 / 50 page

160

140

120

100

Board Copper Area (

)

DCQ

DRV

DRB

RθJA value at board size of 9 in2 (that is, 3 in × 3 in) is a JEDEC standard.

Figure 7-9. RθJA vs Board Size

Figure 7-9 shows the variation of RθJA as a function of ground plane copper area in the board. Figure 7-9 is

intended only as a guideline to demonstrate the effects of heat spreading in the ground plane and is not intended

to be used to estimate actual thermal performance in real application environments.

Note

When the device is mounted on an application PCB, use ΨJT and ΨJB, as explained in the Thermal

Information table.

7.5.1.2 Thermal Protection

Thermal protection disables the output when the junction temperature rises to approximately 160°C, allowing

the device to cool. When the junction temperature cools to approximately 140°C, the output circuitry is again

enabled. Depending on power dissipation, thermal resistance, and ambient temperature, the thermal protection

circuit can cycle on and off. This cycling limits the dissipation of the regulator, protecting the regulator from

damage caused by overheating.

Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate

heat sink. For reliable operation, limit junction temperature to 125°C maximum. To estimate the margin of safety

in a complete design (including heat sink), increase the ambient temperature until the thermal protection is

triggered; use worst-case loads and signal conditions. For good reliability, thermal protection must trigger at least

35°C above the maximum expected ambient condition of the application. This buffer 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 TPS737 is designed to protect against overload conditions. This circuitry is

not intended to replace proper heat sinking. Continuously running the TPS737 into thermal shutdown degrades

device reliability.

7.5.1.3 Estimating Junction Temperature

Using the thermal metrics ΨJT and ΨJB, as shown in the Thermal Information table, the junction temperature can

be estimated with corresponding formulas (given in Equation 8). For backward compatibility, an older θJC,Top

parameter is listed as well.

:T =T +

(8)

where:

• PD is the power dissipation shown by Equation 6

• TT is the temperature at the center-top of the device package

TPS737

SBVS067W – JANUARY 2006 – REVISED AUGUST 2025

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