ADP5022ACBZ-1-R7 datasheet(21/28 Pages) AD

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ADP5022

Rev. A | Page 21 of 28

Input and Output Capacitor Properties

Use the following equation to determine the worst-case capa-

citance accounting for capacitor variation over temperature,

component tolerance, and voltage.

Use any good quality ceramic capacitors with the ADP5022

as long as they meet the minimum capacitance and maximum

ESR requirements. Ceramic capacitors are manufactured with

a variety of dielectrics, each with a different behavior over

temperature and applied voltage. Capacitors must have a

dielectric adequate to ensure the minimum capacitance over

the necessary temperature range and dc bias conditions. X5R

or X7R dielectrics with a voltage rating of 6.3 V or 10 V are

recommended for best performance. Y5V and Z5U dielectrics

are not recommended for use with any LDO because of their

poor temperature and dc bias characteristics.

CEFF = CBIAS × (1 − TEMPCO) × (1 − TOL)

where:

CBIAS is the effective capacitance at the operating voltage.

TEMPCO is the worst-case capacitor temperature coefficient.

TOL is the worst-case component tolerance.

In this example, the worst-case temperature coefficient

(TEMPCO) over −40°C to +85°C is assumed to be 15% for an

X5R dielectric. The tolerance of the capacitor (TOL) is assumed

to be 10% and CBIAS is 0.94 μF at 1.8 V as shown in Figure 51.

Figure 51 depicts the capacitance vs. voltage bias characteristic

of a 0402 1 μF, 10 V, X5R capacitor. The voltage stability of a

capacitor is strongly influenced by the capacitor size and voltage

rating. In general, a capacitor in a larger package or higher voltage

rating exhibits better stability. The temperature variation of the

X5R dielectric is about ±15% over the −40°C to +85°C tempera-

ture range and is not a function of package or voltage rating.

Substituting these values into the following equation.

CEFF = 0.94 μF × (1 − 0.15) × (1 − 0.1) = 0.719 μF

Therefore, the capacitor chosen in this example meets the

minimum capacitance requirement of the LDO over

temperature and tolerance at the chosen output voltage.

To guarantee the performance of the ADP5022, it is imperative

that the effects of dc bias, temperature, and tolerances on the

behavior of the capacitors are evaluated for each application.

1.2

1.0

0.8

0.6

0.4

0.2

DC BIAS VOLTAGE (V)

Figure 51. Capacitance vs. Voltage Characteristic

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