Datasheet

APPLICATION INFORMATION
TPS737xx
GNDEN
IN OUT
V
IN
V
OUT
ON
OFF
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.
Optionaloutputcapacitor.
Mayimproveloadtransient,
noise,orPSRR.
Optionalcapacitor
reducesoutputnoise
andimproves
transientresponse.
OFF
ON
Input and Output Capacitor Requirements
TPS73719-Q1
TPS73733-Q1
www.ti.com ........................................................................................................................................................................................... SBVS123 – DECEMBER 2008
The TPS737xx belongs to a family of new generation LDO regulators that use an NMOS pass transistor to
achieve ultra-low-dropout performance, reverse current blockage, and freedom from output capacitor constraints.
These features combined with an enable input make the TPS737xx ideal for portable applications. This regulator
family offers a wide selection of fixed output voltage versions and an adjustable output version. All versions have
thermal and over-current protection, including foldback current limit.
Figure 31 shows the basic circuit connections for the fixed voltage models. Figure 32 gives the connections for
the adjustable output version (TPS73701).
Figure 31. Typical Application Circuit for Fixed-Voltage Versions
Figure 32. Typical Application Circuit for Adjustable-Voltage Version
R
1
and R
2
can be calculated for any output voltage using the formula shown in Figure 32 . Sample resistor values
for common output voltages are shown in Figure 2 .
For best accuracy, make the parallel combination of R
1
and R
2
approximately equal to 19 k Ω . This 19 k Ω , in
addition to the internal 8-k Ω resistor, presents the same impedance to the error amp as the 27-k Ω bandgap
reference output. This impedance helps compensate for leakages into the error amp terminals.
Although an input capacitor is not required for stability if input impedance is very low, it is good analog design
practice to connect a 0.1- µ F to 1- µ F low 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 1.0- µ F output capacitor for stability. 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 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.
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Product Folder Link(s) :TPS73733-Q1