Datasheet

TPS780
GND
EN
V
SET
IN OUT
V High=V
SET OUT(LOW)
V Low=V
SET OUT(HIGH)
V
IN
V
OUT
1 Fm
1 Fm
4.2Vto5.5V 2.2Vto3.3V
t=3
10k RW
L
´
10kW +R
L
C
OUT
´
TPS780
GND
EN
V
SET
IN OUT
V
IN
V
OUT
1 Fm
1 Fm
4.2Vto5.5V 2.2V
TI Information — Selective Disclosure
TPS780 Series
SBVS083D –JANUARY 2007–REVISED SEPTEMBER 2012 www.ti.com
INTERNAL CURRENT LIMIT
The TPS780 series are internally current-limited to
protect the regulator during fault conditions. During
current limit, the output sources a fixed amount of
current that is largely independent of output voltage.
For reliable operation, the device should not be
operated in a current limit state for extended periods
of time.
The PMOS pass element in the TPS780 series has a
built-in body diode that conducts current when the
voltage at OUT exceeds the voltage at IN. This
current is not limited, so if extended reverse voltage
operation is anticipated, external limiting to 5% of
Figure 59. Circuit to Tie Both EN and V
SET
High
rated output current may be appropriate.
DROPOUT VOLTAGE
SHUTDOWN
The TPS780 series use a PMOS pass transistor to
The enable pin (EN) is active high and is compatible
achieve low dropout. When (V
IN
– V
OUT
) is less than
with standard and low-voltage CMOS levels. When
the dropout voltage (V
DO
), the PMOS pass device is
shutdown capability is not required, EN should be
the linear region of operation and the input-to-output
connected to the IN pin, as shown in Figure 58.
resistance is the R
DS(ON)
of the PMOS pass element.
Figure 59 shows both EN and V
SET
connected to IN.
V
DO
approximately scales with output current
The TPS780 series, with internal active output pull-
because the PMOS device behaves like a resistor in
down circuitry, discharges the output to within 5%
dropout. As with any linear regulator, PSRR and
V
OUT
with a time (t) shown in Equation 3:
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,
(3)
available for download from www.ti.com.
Where:
TRANSIENT RESPONSE
R
L
= output load resistance
C
OUT
= output capacitance
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 48.
ACTIVE V
OUT
PULL-DOWN
In the TPS780 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 TPS780 series are stable with no output load.
Traditional PMOS LDO regulators suffer from lower
Figure 58. Circuit Showing EN Tied High when
loop gain at very light output loads. The TPS780
Shutdown Capability is Not Required
series employ 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 47 for the load transient
response.
20 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated