SBVS037P August 2003 – December 2015 TPS732
PRODUCTION DATA.
8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
8.1 Application Information
The TPS732 device belongs to a family of 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 low noise and an enable input, make the TPS732 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 overcurrent protection, including foldback current limit.
8.2 Typical Applications
Figure 31 shows the basic circuit connections for the fixed-voltage models. Figure 32 gives the connections for the adjustable-voltage version (TPS73201).
Figure 31. Typical Application Circuit for Fixed-Voltage Versions
Figure 32. Typical Application Circuit for Adjustable-Voltage Version
8.2.1 Design Requirements
For best accuracy, make the parallel combination of R1 and R2 approximately equal to 19 kΩ. This 19 kΩ, in addition to the internal 8-kΩ resistor, presents the same impedance to the error amp as the 27-kΩ bandgap reference output. This impedance helps compensate for leakages into the error amp terminals.
8.2.2 Detailed Design Procedure
8.2.2.1 Input and Output Capacitor Requirements
Although an input capacitor is not required for stability, it is good analog design practice to connect a 0.1-μF to
1-μF, low 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 TPS732 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 COUT and total ESR drops below 50 nΩF. 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 meets this requirement.
8.2.2.2 Transient Response
The low open-loop output impedance provided by the NMOS pass element in a voltage follower configuration allows operation without an output capacitor for many applications. As with any regulator, the addition of a capacitor (nominal value 1 μF) from the OUT pin to ground reduces undershoot magnitude but increases its duration. In the adjustable version, the addition of a capacitor, CFB, from the OUT pin to the FB pin also improves the transient response.
The TPS732 does not have active pulldown when the output is overvoltage. This feature allows applications that connect higher voltage sources, such as alternate power supplies, to the output. This feature also results in an output overshoot of several percent if the load current quickly drops to zero when a capacitor is connected to the output. The duration of overshoot can be reduced by adding a load resistor. The overshoot decays at a rate determined by output capacitor COUT and the internal/external load resistance. The rate of decay is given by:
(Fixed voltage versions)
(Adjustable voltage version)
8.2.3 Application Curves
