NCP4587
http://onsemi.com
15
APPLICATION INFORMATION
A typical application circuit for NCP4587 series is shown
in Figure 43.
VIN VOUT
CE
GND
C1 C2
1m
VIN VOUT
NCP4587x
AE
1m
Figure 43. Typical Application Schematic
Input Decoupling Capacitor (C1)
A 1 mF ceramic input decoupling capacitor should be
connected as close as possible to the input and ground pin of
the NCP4587. Higher values and lower ESR improves line
transient response.
Output Decoupling Capacitor (C2)
A 1 mF ceramic output decoupling capacitor is sufficient
to achieve stable operation of the IC. If tantalum capacitor
is used, and its ESR is high, the loop oscillation may result.
If output capacitor is composed from few ceramic capacitors
in parallel, the operation can be unstable. The capacitor
should be connected as close as possible to the output and
ground pin. Larger values and lower ESR improves dynamic
parameters.
Enable Operation
Enable pin CE may be used for turning the regulator on
and off. The regulator is switched on when CE pin voltage
is above logic high level. Enable pin has internal pull down
current source. If enable function is not needed connect CE
pin to VIN.
Current Limit
This regulator includes fold-back type current limit
circuit. This type of protection doesn’t limit current up to
current capability in normal operation, but when over
current occurs, the output voltage and current decrease until
the over current condition ends. Typical characteristics of
this protection type can be observed in the Output Voltage
versus Output Current graphs shown in the typical
characteristics chapter of this datasheet.
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.
Auto ECO and Fast Mode
The NCP4587 has two operation modes that have impact
on supply current and transient response at low output
current. These two modes can be selected by AE pin. If AE
pin is at low level or floating Auto ECO mode is available.
Please, see supply current vs. output current charts. If AE pin
is at high level the device works in permanent Fast Transient
Mode.
Thermal
As power across the IC increases, 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 rise for the part.
That is to say, when the device has good thermal
conductivity through the PCB, the junction temperature will
be relatively low with high power dissipation applications.
PCB layout
Make VIN and GND line sufficient. 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.
