TPS77301, TPS77318, TPS77327, TPS77328, TPS77333 WITH RESET OUTPUT

TPS77401, TPS77418, TPS77427, TPS77428, TPS77433 WITH POWER GOOD OUTPUT

250-mA LDO REGULATORS WITH INTEGRATED RESET OR PG

SLVS281A – FEBRUARY 2000 – REVISED MARCH 2000

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

regulator protection

The TPS773xx or TPS774xx 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 TPS773xx or TPS774xx also features internal current limiting and thermal protection. During normal

operation, the TPS773xx or TPS774xx 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,

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

P

D(max) +

T

J

max

* T

A

RqJA

Where:

MSOP with no airflow.

The regulator dissipation is calculated using:

P

D +

V

I *

V

O

I

O

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

thermal protection circuit.