ADP150

Data Sheet

Rev. B | Page 12 of 20

APPLICATIONS INFORMATION

CAPACITOR SELECTION

Output Capacitor

The ADP150 is designed for operation with small, space-saving

ceramic capacitors but functions with most commonly used

capacitors as long as care is taken with regard to the effective

series resistance (ESR) value. The ESR of the output capacitor

affects the stability of the LDO control loop. A minimum of 1 µF

capacitance with an ESR of 1 Ω or less is recommended to

ensure the stability of the ADP150. The 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 ADP150 to large changes in the load current.

Figure 27 and Figure 28 show the transient responses for output

capacitance values of 1 µF and 4.7 µF, respectively.

CH1 100mA

CH2 50mV

M1.0µs

A CH1

100mA

T

716.000µs

1

2

T

1mA TO 150mA LOAD STEP

CH1 100mA

CH2 50mV

M1.0µs

A CH1

108mA

T

240.000ns

1

2

T

1mA TO 150mA LOAD STEP

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 is encountered. If greater than

1 µF of output capacitance is required, increase the input capacitor

to match the output capacitor.

Input and Output Capacitor Properties

Any good quality ceramic capacitors can be used with the ADP150,

as long as they meet the minimum capacitance and maximum

ESR requirements. Ceramic capacitors are manufactured with a

variety of dielectrics, each with 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. Y5V and Z5U

dielectrics are not recommended, due to their poor temperature

and dc bias characteristics.

Figure 29 depicts the capacitance vs. the 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 temperature

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

1.2

1.0

0.8

0.6

0.4

0.2

0

0

2

4

6

8

10

BIAS VOLTAGE (V)

Figure 29. Capacitance vs. Voltage Bias Characteristic

Use Equation 1 to determine the worst-case capacitance,

accounting for capacitor variation over temperature, component

tolerance, and voltage.

(1)

where:

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

Substituting these values in Equation 1 yields

Therefore, the capacitor chosen in this example meets the

minimum capacitance requirement of the LDO over temperature

and tolerance at the chosen output voltage.