LP2992_15 Datasheet, PDF (16/33 Pages) Texas Instruments – LP2992 Micropower 250-mA Low-Noise Ultralow-Dropout Regulator in SOT-23 and WSON Packages Designed for Use with Very Low-ESR Output Capacitors

LP2992
SNVS171H – NOVEMBER 2001 – REVISED JANUARY 2015
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8.2.2 Detailed Design Procedure
8.2.2.1 External Capacitors
Like any low-dropout regulator, the LP2992 requires external capacitors for regulator stability. These capacitors
must be correctly selected for good performance.
8.2.2.1.1 Input Capacitor
An input capacitor whose capacitance is ≥ 1 µF is required between the LP2992 input and ground (the amount of
capacitance may be increased without limit).
This capacitor must be located a distance of not more than 1 cm from the input pin and returned to a clean
analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.
NOTE
Tantalum capacitors can suffer catastrophic failure due to surge current when connected
to a low-impedance source of power (like a battery or very large capacitor). If a tantalum
capacitor is used at the input, it must be specified by the manufacturer to have a surge
current rating sufficient for the application.
There are no requirements for ESR on the input capacitor, but tolerance and temperature coefficient must be
considered when selecting the capacitor to ensure the capacitance will be ≥ 1 µF over the entire operating
temperature range.
8.2.2.1.2 Output Capacitor
The LP2992 is designed specifically to work with ceramic output capacitors, using circuitry that allows the
regulator to be stable across the entire range of output current with an output capacitor whose ESR is as low as
5 mΩ. It may also be possible to use Tantalum or film capacitors at the output, but these are not as attractive for
reasons of size and cost (see Capacitor Characteristics).
The output capacitor must meet the requirement for minimum amount of capacitance and also have an ESR
value which is within the stable range. Curves are provided which show the stable ESR range as a function of
load current (see Figure 35).
Figure 35. Stable ESR Range vs Load Current
The output capacitor must maintain its ESR within the stable region over the full operating temperature range of
the application to assure stability.
The LP2992 requires a minimum of 4.7 µF on the output (output capacitor size can be increased without limit).
It is important to remember that capacitor tolerance and variation with temperature must be taken into
consideration when selecting an output capacitor so that the minimum required amount of output capacitance is
provided over the full operating temperature range. It should be noted that ceramic capacitors can exhibit large
changes in capacitance with temperature (see Capacitor Characteristics).
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