Datasheet

V
N
ǒ
mV
RMS
Ǔ
+ 27
ǒ
mV
RMS
V
Ǔ
V
OUT
(
V
)
V
N
+ 32mV
RMS
(
R
1
) R
2
)
R
2
+ 32mV
RMS
V
OUT
V
REF
TPS73701
GNDEN FB
IN OUT
V
IN
V
OU
T
V
OUT
= x1.204
(R
1
+ R
2
)
R
2
R
1
C
FB
R
2
Optionalinputcapacitor.
Mayimprovesource
impedance,noise,orPSRR.
Outputcapacitor
mustbe 1.0 F.³ m
Optionalcapacitor
reducesoutputnoise
andimproves
transientresponse.
OFF
ON
TPS737xx
GNDEN
IN OUT
V
IN
V
OUT
ON
OFF
TPS737xx
SBVS067P –JANUARY 2006–REVISED JULY 2013 www.ti.com
APPLICATION INFORMATION
The TPS737xx belongs to a family of new generation For best accuracy, make the parallel combination of
LDO regulators that use an NMOS pass transistor to R
1
and R
2
approximately equal to 19kΩ. This 19kΩ,
achieve ultra-low-dropout performance, reverse in addition to the internal 8kΩ resistor, presents the
current blockage, and freedom from output capacitor same impedance to the error amp as the 27kΩ
constraints. These features combined with an enable bandgap reference output. This impedance helps
input make the TPS737xx ideal for portable compensate for leakages into the error amp
applications. This regulator family offers a wide terminals.
selection of fixed output voltage versions and an
adjustable output version. All versions have thermal
INPUT AND OUTPUT CAPACITOR
and over-current protection, including foldback
REQUIREMENTS
current limit.
Although an input capacitor is not required for stability
Figure 31 shows the basic circuit connections for the
if input impedance is very low, it is good analog
fixed voltage models. Figure 32 gives the connections
design practice to connect a 0.1μF to 1μF low
for the adjustable output version (TPS73701).
equivalent series resistance (ESR) capacitor across
the input supply near the regulator. This capacitor
counteracts reactive input sources and improves
transient response, noise rejection, and ripple
rejection. A higher-value capacitor may be necessary
if large, fast rise-time load transients are anticipated
or the device is located several inches from the
power source.
The TPS737xx requires a 1.0µF output capacitor for
stability. It is designed to be stable for all available
Figure 31. Typical Application Circuit for Fixed-
Voltage Versions types and values of capacitors. In applications where
multiple low ESR capacitors are in parallel, ringing
may occur when the product of C
OUT
and total ESR
drops below 50nΩF. Total ESR includes all parasitic
resistances, including capacitor ESR and board,
socket, and solder joint resistance. In most
applications, the sum of capacitor ESR and trace
resistance will meet this requirement.
OUTPUT NOISE
A precision bandgap reference is used to generate
the internal reference voltage, V
REF
. This reference is
the dominant noise source within the TPS737xx and
it generates approximately 32μV
RMS
(10Hz to
100kHz) at the reference output (NR). The regulator
control loop gains up the reference noise with the
Figure 32. Typical Application Circuit for
same gain as the reference voltage, so that the noise
Adjustable-Voltage Version
voltage of the regulator is approximately given by:
R
1
and R
2
can be calculated for any output voltage
(1)
using the formula shown in Figure 32. Sample
resistor values for common output voltages are
Since the value of V
REF
is 1.2V, this relationship
shown in Figure 2.
reduces to:
(2)
for the case of no C
NR
.
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