Datasheet

www.ti.com
Power Dissipation and Junction Temperature
P
D(max)

T
J
max T
A
R
JA
(2)
P
D


V
I
V
O

 I
O
(3)
TPS70145, TPS70148
TPS70151, TPS70158
TPS70102
SLVS222D – DECEMBER 1999 – REVISED NOVEMBER 2004
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, P
D(max)
, and the actual dissipation, P
D
, which must be less than or
equal to P
D(max)
.
The maximum-power-dissipation limit is determined using Equation 2 :
where:
• T
Jmax
is the maximum allowable junction temperature
• R
θ JA
is the thermal resistance junction-to-ambient for the package; that is, 32.6 ° C/W for the 20-terminal PWP
with no airflow
• T
A
is the ambient temperature
The regulator dissipation is calculated using Equation 3 :
Power dissipation resulting from quiescent current is negligible. Excessive power dissipation will trigger the
thermal protection circuit.
31