TPS79718 Datasheet, PDF (9/13 Pages) Texas Instruments – ULTRALOW-POWER SC70/SOT-323 PACKAGED 10 mA LDO LINEAR REGULATORS WITH POWER GOOD OUTPUT

TPS79718
TPS79730
TPS79733
SLVS332B – MARCH 2001 – REVISED JUNE 2001
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,
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:
PD(max)
+
TJmax *
R_θJA
TA
Where:
T_Jmax is the maximum allowable junction temperature.
R_θJA is the thermal resistance junction-to-ambient for the package (see Power Dissipation Rating Table).
T_A is the ambient temperature.
The regulator dissipation is calculated using:
PD + ^ǒVI * VO^Ǔ IO
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:
D Regulated output voltage that protects the device from battery droop and noise on the line (e.g., switch
bounce)
D Smooth, monotonic power up
D PG signal for controlled device RESET
D Potential to use an existing 5-V power rail to power a 3.3-V or lower device
D Potential to provide separate digital and analog power and ground supplies for a system with only one power
source
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