Datasheet

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APPLICATION INFORMATION
INPUT AND OUTPUT CAPACITOR
OUTPUT NOISE
TPS731xx
GNDEN NR
IN OUT
V
IN
V
OUT
Optional input capacitor.
May improve source
impedance, noise, or PSRR.
Optional output capacitor.
May improve load transient,
noise, or PSRR.
Optional bypass
capacitor to reduce
output noise.
V
N
+ 32mV
RMS
(R
1
) R
2
)
R
2
+ 32mV
RMS
V
OUT
V
REF
(1)
V
N
(mV
RMS
) + 27
ǒ
mV
RMS
V
Ǔ
V
OUT
(V)
(2)
TPS73101
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.
Optionaloutputcapacitor.
Mayimproveloadtransient
noise,orPSRR.
Optionalcapacitor
reducesoutputnoise
andimproves
transientresponse.
V
N
(mV
RMS
) + 8.5
ǒ
mV
RMS
V
Ǔ
V
OUT
(V)
(3)
TPS73101-EP , , TPS73115-EP
TPS731125-EP , TPS73118-EP , TPS73125-EP , TPS73130-EP
TPS73132-EP , TPS73133-EP , TPS73150-EP
SGLS347A – JUNE 2006 – REVISED SEPTEMBER 2007
The TPS731xx belongs to a family of new generation
LDO regulators that use an NMOS pass transistor to
REQUIREMENTS
achieve ultra-low-dropout performance, reverse
current blockage, and freedom from output capacitor
Although an input capacitor is not required for
constraints. These features, combined with low noise
stability, it is good analog design practice to connect
and an enable input, make the TPS731xx ideal for
a 0.1 μ F to 1 μ F low ESR capacitor across the input
portable applications. This regulator family offers a
supply near the regulator. This counteracts reactive
wide selection of fixed output voltage versions and an
input sources and improves transient response, noise
adjustable output version. All versions have thermal
rejection, and ripple rejection. A higher-value
and over-current protection, including foldback
capacitor may be necessary if large, fast rise-time
current limit.
load transients are anticipated or the device is
located several inches from the power source.
Figure 32 shows the basic circuit connections for the
fixed voltage models. Figure 33 gives the connections
The TPS731xx does not require an output capacitor
for the adjustable output version (TPS73101).
for stability and has maximum phase margin with no
capacitor. It is designed to be stable for all available
types and values of capacitors. In applications where
V
IN
– V
OUT
< 0.5 V and multiple low ESR capacitors
are in parallel, ringing may occur when the product of
C
OUT
and total ESR drops below 50 n Ω F. 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.
A precision band-gap reference is used to generate
the internal reference voltage, V
REF
. This reference is
the dominant noise source within the TPS731xx and
Figure 32. Typical Application Circuit for
it generates approximately 32 μ V
RMS
(10 Hz to
Fixed-Voltage Versions
100 kHz) at the reference output (NR). The regulator
control loop gains up the reference noise with the
same gain as the reference voltage, so that the noise
voltage of the regulator is approximately given by:
Since the value of V
REF
is 1.2 V, this relationship
reduces to:
for the case of no C
NR
.
An internal 27 k Ω resistor in series with the noise
Figure 33. Typical Application Circuit for
reduction pin (NR) forms a low-pass filter for the
Adjustable-Voltage Versions
voltage reference when an external noise reduction
capacitor, C
NR
, is connected from NR to ground. For
R
1
and R
2
can be calculated for any output voltage
C
NR
= 10 nF, the total noise in the 10 Hz to 100 kHz
using the formula shown in Figure 33 . Sample
bandwidth is reduced by a factor of ~3.2, giving the
resistor values for common output voltages are
approximate relationship:
shown in Figure 3 . For the best accuracy, make the
parallel combination of R
1
and R
2
approximately
19 k Ω .
for C
NR
= 10nF.
Copyright © 2006 – 2007, Texas Instruments Incorporated Submit Documentation Feedback 13
Product Folder Link(s): TPS73101-EP TPS73115-EP TPS731125-EP TPS73118-EP TPS73125-EP TPS73130-EP
TPS73132-EP TPS73133-EP TPS73150-EP