Datasheet

+
C
1
0.1 Fm
PG
OUT
4
3
IN
NC
GND
2
1
5
V
OUT
TPS797xx
100kW
-
0.47 Fm
P =(V -V )xI
D I O O
P =
D(max)
T max T
R
J A
JA
-
q
TPS797xx
www.ti.com SLVS332I –MARCH 2001–REVISED OCTOBER 2013
APPLICATION INFORMATION
The TPS797xx family of low-dropout (LDO) regulators The maximum-power-dissipation limit is determined
have been optimized for use in micropower using the following equation:
applications. They feature extremely low dropout
voltages and ultralow quiescent current (1.2μA
(1)
typically).
Where:
A typical application circuit is shown in Figure 14.
T
J
max is the maximum allowable junction
temperature.
R
θJA
is the thermal resistance junction-to-ambient for
the package (see Package Dissipation Ratings).
T
A
is the ambient temperature.
The regulator dissipation is calculated using:
(2)
Power dissipation resulting from quiescent current is
negligible.
Regulator Protection
The TPS797xx PMOS-pass transistor has a built-in
back diode that conducts reverse current when the
Figure 14. Typical Application Circuit
input voltage drops below the output voltage (for
example, during power down). Current is conducted
from the output to the input and is not internally
External Capacitor Requirements
limited. If extended reverse voltage operation is
anticipated, external limiting might be appropriate.
Although not required, a 0.1μF or larger input bypass
capacitor, connected between IN and GND and
The TPS797xx features internal current limiting.
located close to the TPS797xx, is recommended,
During normal operation, the TPS797xx limits output
especially when a highly resistive power supply is
current to approximately 190mA. When current
powering the LDO in addition to other devices. Like
limiting engages, the output voltage scales back
all low-dropout regulators, the TPS797xx requires an
linearly until the overcurrent condition ends. Take
output capacitor connected between OUT and GND
care not to exceed the power dissipation ratings of
to stabilize the internal control loop. The minimum
the package.
recommended capacitance is 0.47μF. Any 0.47μF
capacitor is suitable. Capacitor values larger than
Microcontroller Application
0.47μF are acceptable.
One application for which this device is particularly
suited is providing a regulated input voltage and
Power Dissipation and Junction Temperature
power good (PG) supervisory signal to low-power
Specified regulator operation is assured to a junction
devices such as mixed-signal microcontrollers. The
temperature of +85°C; restrict the maximum junction
quiescent or ground current of the TPS797xx family is
temperature to +85°C under normal operating
typically 1.2μA even at full load; therefore, the
conditions. This restriction limits the power dissipation
reduction in battery life by including the TPS797xx in
the regulator can handle in any given application. To
the system is negligible.
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)
.
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