ADP221ACDZ-1818-R7 datasheet(12/20 Pages) AD

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ADP220/ADP221

Data Sheet

Rev. H | Page 12 of 20

APPLICATIONS INFORMATION

CAPACITOR SELECTION

Output Capacitor

The ADP220/ADP221 are designed for operation with small,

space-saving ceramic capacitors, but the parts function with

most commonly used capacitors as long as care is taken with

regards to the effective series resistance (ESR) value. The ESR

of the output capacitor affects stability of the LDO control loop.

A minimum of 0.70 µF capacitance with an ESR of 1 Ω or less

is recommended to ensure stability of the ADP220/ADP221.

Transient response to changes in load current is also affected by

output capacitance. Using a larger value of output capacitance

improves the transient response of the ADP220/ADP221 to large

changes in the load current. Figure 29 and Figure 30 show the

transient responses for output capacitance values of 1 µF and

4.7 µF, respectively.

CH1

200mA ΩBW CH2 50.0mV BW

CH3 10.0mV

M200ns A CH1

132mA

T 26.60%

ILOAD1 = 1mA TO 200mA, ILOAD2 = 1mA

ILOAD1

VOUT1

VOUT2, COUT = 1µF

Figure 29. Output Transient Response

ILOAD1 = 1 mA to 200 mA, ILOAD2 = 1 mA

CH1 = ILOAD1, CH2 = VOUT1, CH3 = VOUT2, COUT = 1 µF

CH1

200mA ΩBW CH2 50.0mV BW

CH3 10.0mV

M1.00µs A CH1

132mA

T 11.40%

ILOAD1 = 1mA TO 200mA, ILOAD2 = 1mA

ILOAD1

VOUT1

VOUT2, COUT = 4.7µF

Figure 30. Output Transient Response

ILOAD1 = 1 mA to 200 mA, ILOAD2 = 1 mA

CH1 = ILOAD1, CH2 = VOUT1, CH3 = VOUT2, COUT = 4.7 µF

Input Bypass Capacitor

Connecting a 1 µF capacitor from VIN to GND reduces the

circuit sensitivity to the PCB layout, especially when long input

traces or high source impedance are encountered. If an output

capacitance greater than 1 µF is required, the input capacitor

should be increased to match it.

Input and Output Capacitor Properties

Any good quality ceramic capacitor can be used with the ADP220/

ADP221, as long as the capacitor meets the minimum capacit-

ance 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 an adequate dielectric 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. Y5V and Z5U dielectrics are not recommended,

due to their poor temperature and dc bias characteristics.

Figure 31 depicts the capacitance vs. voltage bias characteristic

of an 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 the package or voltage rating.

1.2

1.0

0.8

0.6

0.4

0.2

VOLTAGE (V)

Figure 31. Capacitance vs. Voltage Bias Characteristic

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