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OUTPUTVOLTAGE
PROGRAMMINGGUIDE
V
O
V
I
OUT
FB
R1
R2
GND
EN
IN
<0.5V
>2.7 V
TPS70702
0.1 mF
+
OUTPUT
VOLTAGE
R1 R2
2.5 V
3.3 V
3.6 V
UNIT
174
287
324
169
169
169
kW
kW
kW
Regulator Protection
Power Dissipation and Junction Temperature
P
D(max)
+
T
J
max *T
A
R
qJA
(2)
P
D
+
ǒ
V
I
*V
O
Ǔ
I
O
(3)
TPS70745, TPS70748
TPS70751, TPS70758
TPS70702
SLVS291D – MAY 2000 – REVISED DECEMBER 2007
Figure 46. TPS70702 Adjustable LDO Regulator Programming
Both TPS707xx PMOS-pass transistors have built-in back diodes that conduct reverse currents when the input
voltage drops below the output voltage (for example, during power-down). Current is conducted from the output
to the input and is not internally limited. When extended reverse voltage is anticipated, external limiting may be
appropriate.
The TPS707xx also features internal current limiting and thermal protection. During normal operation, the
TPS707xx regulator 1 limits output current to approximately 1.6A (typ) and regulator 2 limits output current to
approximately 750mA (typ). When current limiting engages, the output voltage scales back linearly until the
overcurrent condition ends. While current limiting is designed to prevent gross device failure, care should be
taken not to exceed the power dissipation ratings of the package. If the temperature of the device exceeds
+150 ° C (typ), thermal-protection circuitry shuts it down. Once the device has cooled below +130 ° C (typ),
regulator operation resumes.
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 triggers the thermal
protection circuit.
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