POWER DISSIPATION AND JUNCTION TEMPERATURE

P

D max +

T

J max *TA

R

Q

JA

(3)

P

D

+ VIN*VOUT

I

OUT

(4)

TPS767D3xx

www.ti.com......................................................................................................................................................... SLVS209H – JULY 1999 – REVISED AUGUST 2008

Specified regulator operation is assured to a junction temperature of +125°C; the maximum junction temperature

should be restricted to +125°C under normal operating conditions. This restriction limits the power dissipation the

regulator can handle in any given application. To ensure the junction temperature is within acceptable limits,

calculate the maximum allowable dissipation, PDmax, and the actual dissipation, PD, which must be less than or

equal to PDmax.

The maximum-power-dissipation limit is determined using the following equation:

Where:

• T

Jmax is the maximum allowable junction temperature.

• RθJA is the thermal resistance junction-to-ambient for the package, that is, 28°C/W for the 28-terminal PWP

with no airflow.

• T

A is the ambient temperature.

The regulator dissipation is calculated using:

Power dissipation resulting from quiescent current is negligible. Excessive power dissipation will trigger the

thermal protection circuit.

Copyright © 1999–2008, Texas Instruments Incorporated

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