TPS78218 Datasheet, PDF (11/25 Pages) Texas Instruments – 500nA, IQ 150mA, Ultra-Low Quiescent Current Low-Dropout Linear Regulator

TPS782xx
www.ti.com
SHUTDOWN
The enable pin (EN) is active high and is compatible
with standard and low-voltage CMOS levels. When
shutdown capability is not required, EN should be
connected to the IN pin, as shown in Figure 23. The
TPS782 series, with internal active output pull-down
circuitry, discharges the output to within 5% V_OUT with
a time (t) shown in Equation 1:
t=3
10kW ´ R_L
10kW + R_L
´
C
OUT
(1)
Where:
R_L= output load resistance
C_OUT = output capacitance
4.2V to 5.5V
V_IN
IN
OUT
1mF
TPS78227
2.7V
1mF
V_OUT
EN
GND
Figure 23. Circuit Showing EN Tied High when
Shutdown Capability is Not Required
SBVS115B – AUGUST 2008 – REVISED MAY 2010
DROPOUT VOLTAGE
The TPS782 series use a PMOS pass transistor to
achieve low dropout. When (V_IN – V_OUT) is less than
the dropout voltage (V_DO), the PMOS pass device is
the linear region of operation and the input-to-output
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
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
Typical Characteristics section. Refer to application
report SLVA207, Understanding LDO Dropout,
available for download from www.ti.com.
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.
MINIMUM LOAD
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.
Copyright © 2008–2010, Texas Instruments Incorporated
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