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

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.