Datasheet

DROPOUT VOLTAGE ACTIVE V
OUT
PULL-DOWN
MINIMUM LOAD
TRANSIENT RESPONSE
TPS781 Series
SBVS102B – MARCH 2008 – REVISED MAY 2008 ........................................................................................................................................................... www.ti.com
The TPS781 series use a PMOS pass transistor to In the TPS781 series, the active pull-down discharges
achieve low dropout. When (V
IN
– V
OUT
) is less than V
OUT
when the device is off. However, the input
the dropout voltage (V
DO
), the PMOS pass device is voltage must be greater than 2.2V for the active
the linear region of operation and the input-to-output pull-down to work.
resistance is the R
DS(ON)
of the PMOS pass element.
V
DO
approximately scales with output current
because the PMOS device behaves like a resistor in
The TPS781 series are stable with no output load.
dropout. As with any linear regulator, PSRR and
Traditional PMOS LDO regulators suffer from lower
transient response are degraded as (V
IN
– V
OUT
)
loop gain at very light output loads. The TPS781
approaches dropout. This effect is shown in the
employs an innovative, low-current circuit under very
Typical Characteristics section. Refer to application
light or no-load conditions, resulting in improved
report SLVA207, Understanding LDO Dropout,
output voltage regulation performance down to zero
available for download from www.ti.com .
output current. See Figure 41 for the load 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 42 .
16 Submit Documentation Feedback Copyright © 2008, Texas Instruments Incorporated