TPS767D301, TPS767D318, TPS767D325

DUAL-OUTPUT LOW-DROPOUT VOLTAGE REGULATORS

SLVS209B – JULY 1999 – REVISED APRIL 2000

17

POST OFFICE BOX 655303

Reset indicator

The TPS767D3xx 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 95% (typical) of its 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.

regulator protection

The TPS767D3xx PMOS-pass transistor has a built-in back-gate diode that safely 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 TPS767D3xx also features internal current limiting and thermal protection. During normal operation, the

TPS767D3xx limits 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.