NCP51460

http://onsemi.com

8

APPLICATIONS INFORMATION

It is recommended to connect a 0.1

mF Ceramic capacitor

provide a low impedance path for unwanted AC signals or

noise present on the input voltage. The input capacitor will

also limit the influence of input trace inductances and Power

Supply resistance during sudden load current changes.

Higher capacitances will improve the Power Supply

Rejection Ratio and line transient response.

The NCP51460 was designed to be stable without an

additional output capacitor. Without the output capacitor the

can be as short as 20

ms (Refer to Figure 24 and 25). The

show good stability of NCP51460 even for fast output

deviations during load current changes are required, it is

possible to add some external capacitance as shown on

Figure 26.

NCP51460

GND

3.3 V

0.1 mF

(3.3 V fixed)

Figure 26. Output Capacitor Connection

will increase the settling time and can introduce some

ringing of the output voltage during fast load transients.

NCP51460 behavior for different values of ceramic X7R

output capacitors is depicted on Figure 23.

The Output Voltage ringing and settling times can be

reduced by using some additional resistance in series with

the Ceramic Capacitor or by using Tantalum or Aluminum

Capacitors which have higher ESR values. Figure 27 below

shows the Load Transient improvement after adding an

additional 2

W series resistor to a 1 mF Ceramics Capacitor.

3.35

3.30

3.25

3.35

3.30

3.25

Figure 27.

TIME (50 ms/DIV)

The device was determined to be stable with Aluminum,

Ceramic and Tantalum Capacitors with capacitances

ranging from 0 to 100

Turn−On Response

It is possible to achieve very fast Turn−On time when fast

Figure 24. However if the Input Voltage change from 0 V to

nominal Input Voltage is extremely fast, the Output Voltage

settling time will increase. Figure 28 below shows this effect

when the Input Voltage change is 5.8 V / 2

ms.

0

1

2

3

0

2

4

6

TIME (10 ms/DIV)

Figure 28.