NCP4680 데이터 시트보기 (PDF) - ON Semiconductor

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NCP4680

150 mA, Low Noise Low Dropout Regulator

ON Semiconductor 

NCP4680

APPLICATION INFORMATION

A typical application circuit for NCP4680 series is shown

in Figure 55.

VIN

NCP4680x

VOUT

VIN

VOUT

C1

100n

CE

GND

C2

100n

start−up into at least double the minimum equivalent load.

The minimum equivalent resistance can be computed by

formula 1:

VOUT(NOM)

REQMIN + IOUTMAX

(eq. 1)

This leads us to the result that the minimum equivalent

start up resistance for VOUT(NOM) < 1.8 V is:

RSUMIN + 2 @ REQMIN

(eq. 2)

Figure 55. Typical Application Schematic

Input Decoupling Capacitor (C1)

A 0.1 mF ceramic input decoupling capacitor should be

connected as close as possible to the input and ground pin of

the NCP4680. Higher values and lower ESR improves line

transient response.

Output Decoupling Capacitor (C2)

A 0.1 mF ceramic output decoupling capacitor is enough

to achieve stable operation of the IC. If a tantalum capacitor

is used, and its ESR is high, loop oscillation may result. The

capacitors should be connected as close as possible to the

output and ground pins. Larger values and lower ESR

improves dynamic parameters.

Current Limit

The NCP4680 includes fold−back type current limit

protection. Its typical characteristic for 0.8 V version is

shown in Figure 3. The advantage of this protection is that

power loss at the regulator is minimized at over current or

short circuit conditions. When the over current or short

circuit event disappears, the regulator reverts from fold back

to regulation. This kind of current limit may cause issues at

start−up for voltage versions below 1.8 V and some load

types: for these lower voltage options it is recommended to

Enable Operation

The enable pin CE may be used for turning the regulator

on and off. The IC is switched on when a high level voltage

is applied to the CE pin. The enable pin has an internal pull

down current source. If the enable function is not needed

connect CE pin to VIN.

Output Discharger

The D version includes a transistor between VOUT and

GND that is used for faster discharging of the output

capacitor. This function is activated when the IC goes into

disable mode.

Thermal

As power across the IC increase, it might become

necessary to provide some thermal relief. The maximum

power dissipation supported by the device is dependent

upon board design and layout. Mounting pad configuration

on the PCB, the board material, and also the ambient

temperature affect the rate of temperature increase for the

part. When the device has good thermal conductivity

through the PCB the junction temperature will be relatively

low in high power dissipation applications.

PCB layout

Make the VIN and GND line as large as practical. If their

impedance is high, noise pickup or unstable operation may

result. Connect capacitors C1 and C2 as close as possible to

the IC, and make wiring as short as possible.

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