Datasheet

TPS78327
GND
EN
IN OUT
V
IN
V
OUT
1 Fm
1 Fm
4.2Vto5.5V 2.7V
TPS783xx
www.ti.com SBVS133 –FEBRUARY 2010
INTERNAL CURRENT LIMIT TRANSIENT RESPONSE
The TPS783 is internally current-limited to protect the As with any regulator, increasing the size of the
regulator during fault conditions. During current limit, output capacitor reduces over/undershoot magnitude
the output sources a fixed amount of current that is but increases duration of the transient response. For
largely independent of output voltage. For reliable more information, see Figure 17.
operation, the device should not be operated in a
current limit state for extended periods of time.
MINIMUM LOAD
The TPS783 series are stable with no output load.
SHUTDOWN
Traditional PMOS LDO regulators suffer from lower
The enable pin (EN) is active high and is compatible loop gain at very light output loads. The TPS783
with standard and low-voltage CMOS levels. When employs an innovative, low-current circuit under very
shutdown capability is not required, EN should be light or no-load conditions, resulting in improved
connected to the IN pin, as shown in Figure 22. output voltage regulation performance down to zero
output current. See Figure 17 for the load transient
response.
THERMAL INFORMATION
THERMAL PROTECTION
Thermal protection disables the device output when
the junction temperature rises to approximately
+160°C, allowing the device to cool. Once the
junction temperature cools to approximately +140°C,
the output circuitry is enabled. Depending on power
dissipation, thermal resistance, and ambient
Figure 22. Circuit Showing EN Tied High when
temperature, the thermal protection circuit may cycle
Shutdown Capability is Not Required
on and off again. This cycling limits the dissipation of
the regulator, protecting it from damage as a result of
overheating.
DROPOUT VOLTAGE
Any tendency to activate the thermal protection circuit
The TPS783 series use a PMOS pass transistor to
indicates excessive power dissipation or an
achieve low dropout. When (V
IN
– V
OUT
) is less than
inadequate heatsink. For reliable operation, junction
the dropout voltage (V
DO
), the PMOS pass device is
temperature should be limited to +105°C maximum.
the linear region of operation and the input-to-output
To estimate the margin of safety in a complete design
resistance is the R
DS(ON)
of the PMOS pass element.
(including heatsink), increase the ambient
V
DO
approximately scales with output current
temperature until the thermal protection is triggered;
because the PMOS device behaves like a resistor in
use worst-case loads and signal conditions.
dropout. As with any linear regulator, PSRR and
The internal protection circuitry of the TPS783 series
transient response are degraded as (V
IN
– V
OUT
)
has been designed to protect against overload
approaches dropout. This effect is shown in the
conditions. However, it is not intended to replace
Typical Characteristics section. Refer to application
proper heatsinking. Continuously running the TPS783
report SLVA207, Understanding LDO Dropout,
series into thermal shutdown degrades device
available for download from www.ti.com.
reliability.
Copyright © 2010, Texas Instruments Incorporated 11