Datasheet

TPS77101/115/118/127/128/133/150 WITH RESET OUTPUT
TPS77201/215/218/227/228/233/250 WITH POWER GOOD OUTPUT
150-mA LDO REGULATORS WITH 8-PIN MSOP PACKAGING
SLVS225D – FEBRUARY 2000 – REVISED OCTOBER 2000
16
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
external capacitor requirements
An input capacitor is not usually required; however, a bypass capacitor (0.047 µF or larger) improves load
transient response and noise rejection if the TPS771xx or TPS772xx is located more than a few inches from
the power supply. A higher-capacitance capacitor may be necessary if large (hundreds of milliamps) load
transients with fast rise times are anticipated.
Most low noise LDOs require an external capacitor to further reduce noise. This will impact the cost and board
space. The TPS771xx and TPS772xx have very low noise specification requirements without using any external
components.
Like all low dropout regulators, the TPS771xx or TPS772xx requires an output capacitor connected between
OUT (output of the LDO) and GND (signal ground) to stabilize the internal control loop. The minimum
recommended capacitance value is 1 µF provided the ESR meets the requirement in Figures 19 and 21. In
addition, a low-ESR capacitor can be used if the capacitance is at least 10 µF and the ESR meets the
requirements in Figures 18 and 20. Solid tantalum electrolytic, aluminum electrolytic, and multilayer ceramic
capacitors are all suitable, provided they meet the requirements described previously.
Ceramic capacitors have different types of dielectric material with each exhibiting different temperature and
voltage variation. The most common types are X5R, X7R, Y5U, Z5U, and NPO. The NPO type ceramic type
capacitors are generally the most stable over temperature. However, the X5R and X7R are also relatively stable
over temperature (with the X7R being the more stable of the two) and are therefore acceptable to use. The Y5U
and Z5U types provide high capacitance in a small geometry, but exhibit large variations over temperature;
therefore, the Y5U and Z5U are not generally recommended for use on this LDO. Independent of which type
of capacitor is used, one must make certain that at the worst case condition the capacitance/ESR meets the
requirement specified in Figures 18 – 21.