Datasheet

TPS732xx
GNDEN
ON
OFF
NR
IN OUT
VIN VOUT
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
TPS73201
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.
OFF
ON
V
N
(mV
RMS
) + 27
ǒ
mV
RMS
V
Ǔ
V
OUT
(V)
TPS732xx
SBVS037O –AUGUST 2003–REVISED AUGUST 2010 www.ti.com
APPLICATION INFORMATION
For best accuracy, make the parallel combination of
The TPS732xx belongs to a family of new generation
R
1
and R
2
approximately equal to 19kΩ. This 19kΩ,
LDO regulators that use an NMOS pass transistor to
in addition to the internal 8kΩ resistor, presents the
achieve ultra-low-dropout performance, reverse
same impedance to the error amp as the 27kΩ
current blockage, and freedom from output capacitor
bandgap reference output. This impedance helps
constraints. These features, combined with low noise
compensate for leakages into the error amp
and an enable input, make the TPS732xx ideal for
terminals.
portable applications. This regulator family offers a
wide selection of fixed output voltage versions and an
INPUT AND OUTPUT CAPACITOR
adjustable output version. All versions have thermal
REQUIREMENTS
and over-current protection, including foldback
current limit.
Although an input capacitor is not required for
stability, it is good analog design practice to connect
Figure 31 shows the basic circuit connections for the
a 0.1mF to 1mF low ESR capacitor across the input
fixed voltage models. Figure 32 gives the connections
supply near the regulator. This counteracts reactive
for the adjustable output version (TPS73201).
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 TPS732xx does not require an output capacitor
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
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
Figure 31. Typical Application Circuit for
applications, the sum of capacitor ESR and trace
Fixed-Voltage Versions
resistance will meet this requirement.
OUTPUT NOISE
A precision band-gap reference is used to generate
the internal reference voltage, V
REF
. This reference is
the dominant noise source within the TPS732xx 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
same gain as the reference voltage, so that the noise
voltage of the regulator is approximately given by:
(1)
Since the value of V
REF
is 1.2V, this relationship
Figure 32. Typical Application Circuit for
reduces to:
Adjustable-Voltage Version
R
1
and R
2
can be calculated for any output voltage
(2)
using the formula shown in Figure 32. Sample
for the case of no C
NR
.
resistor values for common output voltages are
shown in Figure 2.
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