Datasheet

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Power Dissipation and Junction Temperature
P
D(max)
+
T
J
max * T
A
R
θJA
(1)
P
D
+
ǒ
V
I
* V
O
Ǔ
I
O
(2)
Programming the TPS79301 Adjustable LDO Regulator
V
O
+ V
ref
ǒ
1 )
R1
R2
Ǔ
(3)
TPS79301-EP , , TPS79318-EP , , TPS79325-EP , , TPS79328-EP
TPS793285-EP , TPS79330-EP , TPS79333-EP , TPS793475-EP
SGLS163B – APRIL 2003 – REVISED NOVEMBER 2006
APPLICATION INFORMATION (continued)
Specified regulator operation is ensured 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 the following equation:
Where:
T
J
max = Maximum allowable junction temperature
R θ
JA
= Thermal resistance, junction to ambient, for the package, see the dissipation rating table
T
A
= Ambient temperature
The regulator dissipation is calculated using:
Power dissipation resulting from quiescent current is negligible. Excessive power dissipation triggers the thermal
protection circuit.
The output voltage of the TPS79301 adjustable regulator is programmed using an external resistor divider as
shown in Figure 23 . The output voltage is calculated using:
Where:
V
ref
= 1.2246 V typical (the internal reference voltage)
11
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