Datasheet
APPLICATION INFORMATION
Output Noise
V
N
+ 32 mV
RMS
(R
1
) R
2
)
R
2
+ 32 mV
RMS
V
OUT
V
REF
(1)
TPS736xx
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
(mV
RMS
) + 27
ǒ
mV
RMS
V
Ǔ
V
OUT
(V)
(2)
TPS736xx
GNDEN FB
IN OUT
V
IN
V
OUT
V
OUT
=
×
1.204
(R
1
+ R
2
)
R
1
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)
Input and Output Capacitor Requirements
TPS73601-EP , TPS73615-EP , TPS73618-EP
TPS73625-EP , TPS73630-EP , TPS73632-EP , TPS73633-EP
SGLS326C – APRIL 2006 – REVISED FEBRUARY 2009 ..................................................................................................................................................
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supply near the regulator. This counteracts reactive
The TPS736xx belongs to a family of new-generation
input sources and improves transient response, noise
LDO regulators that use an NMOS pass transistor to
rejection, and ripple rejection. A higher-value
achieve ultra-low-dropout performance, reverse
capacitor may be necessary if large, fast rise-time
current blockage, and freedom from output capacitor
load transients are anticipated, or the device is
constraints. These features, combined with low noise
located several inches from the power source.
and an enable input, make the TPS736xx ideal for
portable applications. This regulator family offers a The TPS736xx does not require an output capacitor
wide selection of fixed-output voltage versions and an for stability and has maximum phase margin with no
adjustable-output version. All versions have thermal capacitor. It is designed to be stable for all available
and overcurrent protection, including foldback current types and values of capacitors. In applications where
limit. V
IN
− V
OUT
< 0.5 V and multiple low ESR capacitors
are in parallel, ringing may occur when the product of
Figure 32 shows the basic circuit connections for the
C
OUT
and total ESR drops below 50 Ω . Total ESR
fixed-voltage models. Figure 33 shows the
includes all parasitic resistance, including capacitor
connections for the adjustable-output version
ESR and board, socket, and solder-joint resistance.
(TPS73601). R
1
and R
2
can be calculated for any
In most applications, the sum of capacitor ESR and
output voltage using the formula in Figure 33 . Sample
trace resistance meets this requirement.
resistor values for common output voltages are
shown in Figure 3 . For the best accuracy, make the
parallel combination of R
1
and R
2
approximately 19
k Ω .
A precision band-gap reference is used to generate
the internal reference voltage, V
REF
. This reference is
the dominant noise source within the TPS736xx and
it generates approximately 32 µ V
RMS
(10 Hz to
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
Figure 32. Typical Application Circuit for
reduces to:
Fixed-Voltage Versions
for the case of no C
NR
.
An internal 27-k Ω resistor in series with the noise
reduction pin (NR) forms a low-pass filter for the
voltage reference when an external noise reduction
capacitor, C
NR
, is connected from NR to ground. For
C
NR
= 10 nF, the total noise in the 10-Hz to 100-kHz
bandwidth is reduced by a factor of ~3.2, giving the
approximate relationship:
Figure 33. Typical Application Circuit for
for C
NR
= 10 nF.
Adjustable-Voltage Versions
This noise reduction effect is shown as RMS Noise
Voltage vs C
NR
in Figure 21 .
Although an input capacitor is not required for
stability, it is good analog design practice to connect
a 0.1- µ F to 1- µ F low ESR capacitor across the input
12 Submit Documentation Feedback Copyright © 2006 – 2009, Texas Instruments Incorporated
Product Folder Link(s): TPS73601-EP TPS73615-EP TPS73618-EP TPS73625-EP TPS73630-EP TPS73632-EP
TPS73633-EP