TPS79718

TPS79730

TPS79733

SLVS332B – MARCH 2001 – REVISED JUNE 2001

9

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APPLICATION INFORMATION

power dissipation and junction temperature

Specified regulator operation is assured to a junction temperature of 85

°C; restrict the maximum junction

temperature to 85

°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

RθJA

Where:

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 triggers the

thermal protection circuit.

regulator protection

The TPS797xx PMOS-pass transistor has a built-in back diode that conducts reverse current 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. If extended reverse voltage operation is anticipated, external limiting might

be appropriate.

The TPS797xx features internal current limiting. During normal operation, the TPS797xx limits output current

to approximately 190 mA. When current limiting engages, the output voltage scales back linearly until the

overcurrent condition ends. Take care not to exceed the power dissipation ratings of the package.

microcontroller application

One application for which this device is particularly suited is providing a regulated input voltage and power good

(PG) supervisory signal to low-power devices such as mixed-signal microcontrollers. The quiescent or ground

current of the TPS797xx family is typically 1.2

µA even at full load; therefore, the reduction in battery life by

including the TPS797xx in the system is negligible. The primary benefits of using the TPS797xx to power low

power digital devices include:

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