TPS77501-EP, TPS77515-EP, TPS77516-EP, TPS77518-EP

TPS77525-EP, TPS77533-EP WITH RESET OUTPUT

FAST-TRANSIENT-RESPONSE 500-mA LOW-DROPOUT VOLTAGE REGULATORS

SGLS010B − MARCH 2003 − REVISED JUNE 2010

17

POST OFFICE BOX 655303

APPLICATION INFORMATION

reset indicator

The TPS775xx features a RESET output that can be used to monitor the status of the regulator. The internal

comparator monitors the output voltage: when the output drops to between 92% and 98% of its nominal regulated

value, the RESET output transistor turns on, taking the signal low. The open-drain output requires a pullup resistor.

If not used, it can be left floating. RESET can be used to drive power-on reset circuitry or as a low-battery indicator.

RESET does not assert itself when the regulated output voltage falls outside the specified 2% tolerance, but instead

reports an output voltage low relative to its nominal regulated value (refer to timing diagram for start-up sequence).

regulator protection

The TPS775xx PMOS-pass transistors have 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 TPS775xx also feature internal current limiting and thermal protection. During normal operation, the TPS775xx

limit output current to approximately 1.7 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:

PWP 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.