0402, 6.3V, X5R

0603, 10V, X5R

0

1.0

2.0

3.0

4.0

5.0

DC BIAS (V)

20%

40%

60%

80%

100%

LP3990-Q1

www.ti.com

SNVSA66A – OCTOBER 2014 – REVISED DECEMBER 2015

It is also possible to use tantalum or film capacitors at the device output, but these are not as attractive for

reasons of size and cost (see Capacitor Characteristics).

The output capacitor must meet the requirement for the minimum value of capacitance and also have an ESR

value that is within the range 5 m

Ω to 500 mΩ for stability.

8.2.2.5 No-Load Stability

The LP3990-Q1 remains stable and in regulation with no external load. This is an important consideration in

some circuits, for example CMOS RAM keep-alive applications.

8.2.2.6 Capacitor Characteristics

The LP3990-Q1 is designed to work with ceramic capacitors on the output to take advantage of the benefits they

offer. For capacitance values in the range of 0.47 µF to 4.7 µF, ceramic capacitors are the smallest, least

expensive and have the lowest ESR values, thus making them best for eliminating high frequency noise. The

ESR of a typical 1-µF ceramic capacitor is in the range of 20 m

Ω to 40 mΩ, which easily meets the ESR

requirement for stability for the LP3990-Q1.

For both input and output capacitors, careful interpretation of the capacitor specification is required to ensure

correct device operation. The capacitor value can change greatly, depending on the operating conditions and

capacitor type.

In particular, the output capacitor selection must take account of all the capacitor parameters, to ensure that the

specification is met within the application. The capacitance can vary with DC bias conditions as well as

temperature and frequency of operation. Capacitor values also show some decrease over time due to aging. The

capacitor parameters are also dependant on the particular case size, with smaller sizes giving poorer

performance figures in general. As an example, Figure 14 shows a typical graph comparing different capacitor

case sizes in a Capacitance vs. DC Bias plot. As shown in Figure 14, increasing the DC Bias condition can result

in the capacitance value falling below the minimum value given in the recommended capacitor specifications

table (0.7 µF in this case). Note that the graph shows the capacitance out of spec for the 0402 case size

capacitor at higher bias voltages. It is therefore recommended that the capacitor manufacturers’ specifications for

the nominal value capacitor are consulted for all conditions, as some capacitor sizes (for example, 0402) may not

be suitable in the actual application.

Figure 14. Typical Variation In Capacitance vs DC Bias

Capacitance of the ceramic capacitor can vary with temperature. The capacitor type X7R, which operates over a

temperature range of –55°C to 125°C, only varies the capacitance to within ±15%. The capacitor type X5R has a

similar tolerance over a reduced temperature range of –55°C to 85°C. Many large value ceramic capacitors,

larger than 1 µF are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by

more than 50% as the temperature varies from 25°C to 85°C. Therefore, X7R and X5R types are recommended

over Z5U and Y5V in applications where the ambient temperature changes significantly above or below 25°C.

Tantalum capacitors are less desirable than ceramic for use as output capacitors because they are more

expensive when comparing equivalent capacitance and voltage ratings in the 0.47-µF to 4.7-µF range.

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