Datasheet

TPS71025
LOW-DROPOUT VOLTAGE REGULATOR
SLVS162A – MAY 1997 – REVISED MAY 1998
15
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
external capacitor requirements
An input capacitor is not required; however, a ceramic bypass capacitor (0.047 pF to 0.1 µF) improves load
transient response and noise rejection if the TPS71025 is located more than a few inches from the power supply.
A higher-capacitance electrolytic capacitor may be necessary if large (hundreds of milliamps) load transients
with fast rise times are anticipated.
As with most LDO regulators, the TPS71025 requires an output capacitor for stability. A low-ESR 10-µF
solid-tantalum capacitor connected from the regulator output to ground is sufficient to ensure stability over the
full load range (see Figure 11). Adding high-frequency ceramic or film capacitors (such as power-supply bypass
capacitors for digital or analog ICs) can cause the regulator to become unstable unless the ESR of the tantalum
capacitor is less than 1.2 Ω over temperature. Capacitors with published ESR specifications such as the
AVX TPSD106K035R0300 and the Sprague 593D106X0035D2W work well because the maximum ESR at
25°C is 300 mΩ (typically, the ESR in solid-tantalum capacitors increases by a factor of 2 or less when the
temperature drops from 25°C to –40°C). Where component height and/or mounting area is a problem,
physically smaller, 10-µF devices can be screened for ESR. Figure 7 through Figure 14 show the stable regions
of operation using different values of output capacitance with various values of ceramic load capacitance.
In applications with little or no high-frequency bypass capacitance (< 0.2 µF), the output capacitance can be
reduced to 4.7 µF, provided ESR is maintained between 0.7 and 2.5 Ω. Because minimum capacitor ESR is
seldom if ever specified, it may be necessary to add a 0.5-Ω to 1-Ω resistor in series with the capacitor and limit
ESR to 1.5 Ω maximum. As shown in the ESR graphs (Figure 7 through Figure 14), minimum ESR is not a
problem when using 10-µF or larger output capacitors.
Below is a partial listing of surface-mount capacitors usable with the TPS71025. This information (along with
the ESR graphs, Figure 7 through Figure 14) is included to assist in selection of suitable capacitance for the
application. When necessary to achieve low height requirements along with high output current and/or high
ceramic load capacitance, several higher ESR capacitors can be used in parallel to meet the guidelines above.