Datasheet
TPS78227
GND
EN
IN OUT
V
IN
V
OUT
1 Fm
1 Fm
4.2Vto5.5V 2.7V
t=3
10k RW
L
´
10kW +R
L
C
OUT
´
TPS782xx
SBVS115C –AUGUST 2008–REVISED JANUARY 2014
www.ti.com
SHUTDOWN DROPOUT VOLTAGE
The enable pin (EN) is active high and is compatible The TPS782 series use a PMOS pass transistor to
with standard and low-voltage CMOS levels. When achieve low dropout. When (V
IN
– V
OUT
) is less than
shutdown capability is not required, EN should be the dropout voltage (V
DO
), the PMOS pass device is
connected to the IN pin, as shown in Figure 23. The the linear region of operation and the input-to-output
TPS782 series, with internal active output pull-down resistance is the R
DS(ON)
of the PMOS pass element.
circuitry, discharges the output to within 5% V
OUT
with V
DO
approximately scales with output current
a time (t) shown in Equation 1: because the PMOS device behaves like a resistor in
dropout. As with any linear regulator, PSRR and
transient response are degraded as (V
IN
– V
OUT
)
approaches dropout. This effect is shown in the
(1)
Typical Characteristics section. Refer to application
report SLVA207, Understanding LDO Dropout,
Where:
available for download from www.ti.com.
R
L
= output load resistance
C
OUT
= output capacitance
TRANSIENT RESPONSE
As with any regulator, increasing the size of the
output capacitor reduces over/undershoot magnitude
but increases duration of the transient response. For
more information, see Figure 19.
ACTIVE V
OUT
PULL-DOWN
In the TPS782 series, the active pull-down discharges
V
OUT
when the device is off. However, the input
voltage must be greater than 2.2V for the active pull-
down to work.
Figure 23. Circuit Showing EN Tied High when
MINIMUM LOAD
Shutdown Capability is Not Required
The TPS782 series are stable with no output load.
Traditional PMOS LDO regulators suffer from lower
loop gain at very light output loads. The TPS782
employs an innovative, low-current circuit under very
light or no-load conditions, resulting in improved
output voltage regulation performance down to zero
output current. See Figure 19 for the load transient
response.
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