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%

17

LP38690, LP38692

www.ti.com

SNVS322M – DECEMBER 2004 – REVISED DECEMBER 2015

Product Folder Links: LP38690 LP38692

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Copyright © 2004–2015, Texas Instruments Incorporated

8.2.2.2.2

Output Capacitor

The LP38690 and LP38692 are designed specifically to work with very small ceramic output capacitors. A 1-

μF

ceramic capacitor (temperature types Z5U, Y5V or X7R/X5R) with ESR between 5 m

Ω to 500 mΩ, is suitable in

the LP38690 or LP38692 application circuit.

For this device the output capacitor should be connected between the OUT pin and GND pin. 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.

8.2.2.2.3

No Load Stability

The LP38690 and LP38692 remain stable and in regulation with no external load. This is an important

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

8.2.2.2.4

Capacitor Characteristics

The LP38690 and LP38692 are 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 mΩ to 40 mΩ, which easily meets the ESR

requirement for stability for the LP38690 or LP38692.

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 should 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 shows some decrease over time due to aging.

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

performance figures in general. As an example, Figure 32 shows a typical graph comparing different capacitor

case sizes in a capacitance vs DC bias plot. As shown in Figure 32, 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 32. Typical Variation In Capacitance vs DC Bias

The ceramic capacitor’s value varies 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.