Datasheet

TPS77101/115/118/127/128/133/150 WITH RESET OUTPUT
TPS77201/215/218/227/228/233/250 WITH POWER GOOD OUTPUT
150-mA LDO REGULATORS WITH 8-PIN MSOP PACKAGING
SLVS225D – FEBRUARY 2000 – REVISED OCTOBER 2000
20
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
regulator protection
The TPS771xx or TPS772xx PMOS-pass transistor has a built-in back diode that conducts reverse currents
when the input voltage drops below the output voltage (e.g., 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 TPS771xx or TPS772xx also features internal current limiting and thermal protection. During normal
operation, the TPS771xx or TPS772xx limits output current to approximately 0.9 A. 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.
power dissipation and junction temperature
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 the following equation:
P
D(max)
+
T
J
max * T
A
R
qJA
Where:
T
J
max is the maximum allowable junction temperature.
T
A
is the ambient temperature.
R
θJA
is the thermal resistance junction-to-ambient for the package, i.e., 266.2°C/W for the 8-terminal
MSOP with no airflow.
The regulator dissipation is calculated using:
P
D
+
ǒ
V
I
* V
O
Ǔ
I
O
Power dissipation resulting from quiescent current is negligible. Excessive power dissipation will trigger the
thermal protection circuit.