Datasheet

V
OUT
C
OUT
10 Fm
TPS74801
GND
EN
FB
IN PG
BIAS
SS
OUT
V
IN
R
1
R
2
R
3
C
IN
1 Fm
C
SS
V
BIAS
C
BIAS
1 Fm
V =0.8
OUT
´ 1+
R
1
R
2
)(
TPS74801-Q1
www.ti.com SLVSAI4B –OCTOBER 2010–REVISED JULY 2013
APPLICATION INFORMATION
The TPS74801-Q1 belongs to a family of low dropout regulators that feature soft-start capability. These
regulators use a low current bias input to power all internal control circuitry, allowing the NMOS pass transistor to
regulate very low input and output voltages.
The use of an NMOS-pass FET offers several critical advantages for many applications. Unlike a PMOS topology
device, the output capacitor has little effect on loop stability. This architecture allows the TPS74801-Q1 to be
stable with any capacitor type of value 2.2 μF or greater. Transient response is also superior to PMOS
topologies, particularly for low V
IN
applications.
The TPS74801-Q1 features a programmable voltage-controlled soft-start circuit that provides a 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. An enable (EN) pin with
hysteresis and deglitch allows slow-ramping signals to be used for sequencing the device. The low V
IN
and V
OUT
capability allows for inexpensive, easy-to-design, and efficient linear regulation between the multiple supply
voltages often present in processor-intensive systems.
Figure 25 illustrates the typical application circuit for the TPS74801-Q1 adjustable output device.
Figure 25. Typical Application Circuit for the TPS74801-Q1 (Adjustable)
R
1
and R
2
can be calculated for any output voltage using the formula shown in Figure 25. Refer to Table 1 for
sample resistor values of common output voltages. In order to achieve the maximum accuracy specifications, R
2
should be ≤ 4.99 kΩ.
INPUT, OUTPUT, AND BIAS CAPACITOR REQUIREMENTS
The device is designed to be stable for all available types and values of output capacitors ≥ 2.2 μF. The device is
also stable with multiple capacitors in parallel, which can be of any type or value.
The capacitance required on the IN and BIAS pins strongly depends on the input supply source impedance. To
counteract any inductance in the input, the minimum recommended capacitor for V
IN
and V
BIAS
is 1 μF. If V
IN
and
V
BIAS
are connected to the same supply, the recommended minimum capacitor for V
BIAS
is 4.7 μF. Good quality,
low ESR capacitors should be used on the input; ceramic X5R and X7R capacitors are preferred. These
capacitors should be placed as close the pins as possible for optimum performance.
TRANSIENT RESPONSE
The TPS74801-Q1 was designed to have excellent transient response for most applications with a small amount
of output capacitance. In some cases, the transient response may be limited by the transient response of the
input supply. This limitation is especially true in applications where the difference between the input and output is
less than 300 mV. In this case, adding additional input capacitance improves the transient response much more
than just adding additional output capacitance would do. With a solid input supply, adding additional output
capacitance reduces undershoot and overshoot during a transient event; refer to Figure 22 in the Typical
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