Datasheet

V
N
ǒ
mV
RMS
Ǔ
+ 16
ǒ
mV
RMS
V
Ǔ
V
OUT
(
V
)
TPS744xx
SBVS066O –DECEMBER 2005–REVISED MARCH 2013 www.ti.com
OUTPUT NOISE If not used, EN can be connected to either IN or
BIAS. If EN is connected to IN, it should be
The TPS744xx provides low output noise when a
connected as close as possible to the largest
soft-start capacitor is used. When the device reaches
capacitance on the input to prevent voltage droops on
the end of the soft-start cycle, the soft-start capacitor
that line from triggering the enable circuit.
serves as a filter for the internal reference. By using a
0.001μF soft-start capacitor, the output noise is
POWER-GOOD (QFN Package Only)
reduced by half and is typically 19μV
RMS
for a 1.2V
output (100Hz to 100kHz). Because most of the
The power-good (PG) pin is an open-drain output and
output noise is generated by the internal reference,
can be connected to any 5.5V or lower rail through an
the noise is a function of the set output voltage. The
external pull-up resistor. This pin requires at least
RMS noise with a 0.001μF soft-start capacitor is
1.1V on V
BIAS
in order to have a valid output. The PG
given in Equation 3.
output is high-impedance when V
OUT
is greater than
V
IT
+ V
HYS
. If V
OUT
drops below V
IT
or if V
BIAS
drops
below 1.9V, the open-drain output turns on and pulls
(3) the PG output low. The PG pin also asserts when the
device is disabled. The recommended operating
The low output noise of the TPS744xx makes it a
condition of PG pin sink current is up to 1mA, so the
good choice for powering transceivers, PLLs, or other
pull-up resistor for PG should be in the range of 10kΩ
noise-sensitive circuitry.
to 1MΩ. PG is only provided on the QFN package. If
output voltage monitoring is not needed, the PG pin
ENABLE/SHUTDOWN
can be left floating.
The enable (EN) pin is active high and is compatible
INTERNAL CURRENT LIMIT
with standard digital signaling levels. V
EN
below 0.4V
turns the regulator off, while V
EN
above 1.1V turns the
The TPS744xx features a factory-trimmed, accurate
regulator on. Unlike many regulators, the enable
current limit that is flat over temperature and supply
circuitry has hysteresis and deglitching for use with
voltage. The current limit allows the device to supply
relatively slow-ramping analog signals. This
surges of up to 3.5A and maintain regulation. The
configuration allows the TPS744xx to be enabled by
current limit responds in about 10μs to reduce the
connecting the output of another supply to the EN
current during a short-circuit fault. Recovery from a
pin. The enable circuitry typically has 50mV of
short-circuit condition is well-controlled and results in
hysteresis and a deglitch circuit to help avoid on-off
very little output overshoot when the load is removed.
cycling because of small glitches in the V
EN
signal.
See Figure 29 in the Typical Characteristics section
for short-circuit recovery performance.
The enable threshold is typically 0.8V and varies with
temperature and process variations. Temperature
The internal current limit protection circuitry of the
variation is approximately –1mV/°C; therefore,
TPS744xx is designed to protect against overload
process variation accounts for most of the variation in
conditions. It is not intended to allow operation above
the enable threshold. If precise turn-on timing is
the rated current of the device. Continuously running
required, a fast rise-time signal should be used to
the TPS744xx above the rated current degrades
enable the TPS744xx.
device reliability.
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