ADP1754/ADP1755

Data Sheet

Rev. E | Page 14 of 20

APPLICATIONS INFORMATION

CAPACITOR SELECTION

Output Capacitor

The ADP1754/ADP1755 are designed for operation with small,

space-saving ceramic capacitors, but they can function with most

commonly used capacitors as long as care is taken with the

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

capacitor affects the stability of the LDO control loop. A mini-

mum of 3.3 µF capacitance with an ESR of 500 mΩ or less is

recommended to ensure the stability of the ADP1754/ADP1755.

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 ADP1754/ADP1755 to

large changes in load current. Figure 33 and Figure 34 show the

transient responses for output capacitance values of 4.7 µF and

22 µF, respectively.

1

2

T

B

A CH1

380mA

1mA TO 1.2A LOAD STEP, 2.5A/µs, 500mA/DIV

50mV/DIV

1

2

T

B

A CH1

340mA

1mA TO 1.2A LOAD STEP, 2.5A/µs, 500mA/DIV

20mV/DIV

Input Bypass Capacitor

Connecting a 4.7 µF capacitor from the VIN pin to GND

reduces the circuit sensitivity to printed circuit board (PCB)

layout, especially when long input traces or high source

impedance are encountered. If output capacitance greater than

4.7 µF is required, it is recommended that the input capacitor be

increased to match it.

Input and Output Capacitor Properties

Any good quality ceramic capacitors can be used with the

ADP1754, as long as they meet the minimum capacitance and

maximum ESR requirements. Ceramic capacitors are manufac-

tured 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 recom-

mended. Y5V and Z5U dielectrics are not recommended, due

to their poor temperature and dc bias characteristics.

Figure 35 shows the capacitance vs. voltage bias characteristics

of an 0805 case, 4.7 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 with

a 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 size

or voltage rating.

5

4

3

2

1

0

0

2

4

6

8

10

VOLTAGE BIAS (V)

MURATA P/N GRM219R61A475KE34

Figure 35. Capacitance vs. Voltage Bias Characteristics

Equation 3 can be used to determine the worst-case capacitance,

accounting for capacitor variation over temperature, component

tolerance, and voltage.

(3)

where:

TEMPCO is the worst-case capacitor temperature coefficient.

TOL is the worst-case component tolerance.