Datasheet

APPLICATION INFORMATION
V =
OUT
x0.800,R ~320k
2
W
(R R
1 2
+ )
R
2
(1)
Input and Output Capacitor Requirements
TPS717xx
GNDEN NR
IN OUT
V
IN
V
OUT
1 Fm
Ceramic
V
EN
Optional1.0 Finput
capacitor.Mayimprove
sourceimpedance,noise
orPSRR.
m
Optional0.01 Fbypass
capacitortoreduce
outputnoiseand
increasePSRR.
m
TPS71701
GND
EN FB
IN OUT
V
IN
V
OUT
1 Fm
Ceramic
V
EN
R
1
R
2
Optional1.0 Finput
capacitor.Mayimprove
sourceimpedance,noise
orPSRR.
m
TPS717xx
www.ti.com .................................................................................................................................................. SBVS068G – FEBRUARY 2006 – REVISED APRIL 2009
The TPS717xx belongs to a family of new generation
For the adjustable version (TPS71701), the NR pin is
LDO regulators that use innovative circuitry to
replaced with a feedback (FB) pin. The voltage on
achieve ultra-wide bandwidth and high loop gain,
this pin sets the output voltage and is determined by
resulting in extremely high PSRR (up to 1MHz) at
the values of R
1
and R
2
. The values of R
1
and R
2
can
very low headroom (V
IN
– V
OUT
). Fixed voltage
be calculated for any voltage using the formula given
versions provide a noise reduction pin to bypass
in Equation 1 :
noise generated by the bandgap reference and to
improve PSRR while a quick-start circuit fast-charges
this capacitor. These features, combined with low
noise, enable, low ground pin current, and ultra-small
packaging, make this part ideal for portable
The value of R
2
directly impacts the stability of the
applications. This family of regulators offers
device and should be chosen at approximately 160k Ω
sub-bandgap output voltages, current limit and
or 320k Ω . Sample resistor values for common output
thermal protection, and is fully specified from – 40 ° C
voltages are shown in Table 2 .
to +125 ° C.
Figure 33 shows the basic circuit connections for the
Table 2. Sample 1% Resistor Values for Common
fixed voltage options. Figure 34 gives the connections Output Voltages
for the adjustable output version (TPS71701). Note
V
OUT
R
1
R
2
that the NR pin is not available on the adjustable
1.0 80.6k Ω 324k Ω
version.
1.2 162k Ω 324k Ω
1.5 294k Ω 332k Ω
1.8 402k Ω 324k Ω
2.5 665k Ω 316k Ω
3.3 1.02M Ω 324k Ω
5.0 1.74M Ω 332k Ω
Although an input capacitor is not required for
stability, it is good analog design practice to connect
a 0.1 µ F to 1.0 µ F low equivalent series resistance
(ESR) capacitor across the input supply near the
regulator. This capacitor will counteract reactive input
sources and improve transient response, noise
Figure 33. Typical Application Circuit
rejection, and ripple rejection. A higher-value
(Fixed Voltage Versions)
capacitor may be necessary if large, fast rise-time
load transients are anticipated or if the device is
located several inches from the power source. If
source impedance is not sufficiently low, a 0.1 µ F
input capacitor may be necessary to ensure stability.
The TPS717xx is designed to be stable with standard
ceramic capacitors of values 1.0 µ F or larger. X5R-
and X7R-type capacitors are best because they have
minimal variation in value and ESR over temperature.
Maximum ESR should be < 1.0 Ω .
The TPS717xx implements an innovative internal
compensation circuit that does not require a feedback
capacitor across R
2
for stability. A feedback capacitor
should not be used for this device.
Figure 34. Typical Application Circuit
(Adjustable Voltage Version)
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