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TPS749XX Datasheet(PDF) 10 Page - Texas Instruments

Part No. TPS749XX
Description  3.0A Low Dropout Linear Regulator with Programmable Soft-Start
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Maker  TI [Texas Instruments]
Homepage  http://www.ti.com
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TPS749XX Datasheet(HTML) 10 Page - Texas Instruments

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APPLICATION INFORMATION
INPUT, OUTPUT, AND BIAS CAPACITOR
TRANSIENT RESPONSE
V
OUT
C
OUT
10 F
m
TPS74901
GND
EN
FB
IN
PG
BIAS
SS
OUT
V
IN
R
1
R
2
R
3
C
IN
1 F
m
C
SS
V
BIAS
C
BIAS
1 F
m
V
=0.8
OUT
´
1+
R
1
R
2
)
(
TPS749xx
SBVS082A – JUNE 2007 – REVISED JULY 2007
The TPS749xx belongs to a family of low dropout
REQUIREMENTS
regulators that feature soft-start capabilities. These
regulators use a low current bias input to power all
The device is designed to be stable for all available
internal control circuitry, allowing the NMOS pass
types of and values of output capacitors
≥ 2.2μF.
transistor to regulate very low input and output
The device is also stable with multiple capacitors in
voltages.
parallel, which can be of any type or value.
The use of an NMOS-pass FET offers several critical
The capacitance required on the IN and BIAS pin
advantages for many applications. Unlike a PMOS
strongly
depends
on
the
input
supply
source
topology device, the output capacitor has little effect
impedance. To counteract any inductance in the
on
loop
stability.
This
architecture
allows
the
input, the minimum recommended capacitor for VIN
TPS749xx to be stable with any capacitor type of
and VBIAS is 1μF. If VIN and VBIAS are connected to
value 2.2
μF or greater. Transient response is also
the
same
supply,
the
recommended
minimum
superior to PMOS topologies, particularly for low VIN
capacitor for VBIAS is 4.7μF. Good quality, low ESR
applications.
capacitors should be used on the input; ceramic X5R
and X7R capacitors are preferred. These capacitors
The
TPS749xx
features
a
programmable
should be placed as close the pins as possible for
voltage-controlled soft-start circuit that provides a
optimum performance.
smooth, monotonic start-up and limits startup inrush
currents that may be caused by large capacitive
loads. A power-good (PG) output is available to allow
supply monitoring and sequencing of other supplies.
The
TPS749xx
is
designed
to
have
excellent
An enable (EN) pin with hysteresis and deglitch
transient response for most applications with a small
allows
slow-ramping
signals
to
be
used
for
amount of output capacitance. In some cases, the
sequencing the device. The low VIN and VOUT
transient response may be limited by the transient
capability allows for inexpensive, easy-to-design, and
response of the input supply. This limitation is
efficient linear regulation between the multiple supply
especially true in applications where the difference
voltages
often
present
in
processor
intensive
between the input and output is less than 300mV. In
systems.
this
case,
adding
additional
input
capacitance
improves the transient response much more than just
Figure 25 illustrates the typical application circuit for
adding additional output capacitance would do. With
the TPS749xx adjustable input device.
a
solid
input
supply,
adding
additional
output
R1 and R2 can be calculated for any output voltage
capacitance
reduces
undershoot
and
overshoot
using the formula shown in Figure 25. Refer to
during a transient event; refer to Figure TBD in the
Table 1 for sample resistor values of common output
Typical
Characteristics
section.
Because
the
voltages. In order to achieve the maximum accuracy
TPS749xx is stable with output capacitors as low as
specifications, R2 should be ≤ 4.99kΩ.
2.2
μF, many applications may need very little
capacitance
at
the
LDO
output.
For
these
applications,
local
bypass
capacitance
for
the
powered device may be sufficient to meet the
transient requirements of the application. This design
reduces the total solution cost by avoiding the need
to use expensive high-value capacitors at the LDO
output.
Figure 25. Typical Application Circuit for the
TPS749xx (Adjustable)
10
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