NCP4623 Просмотр технического описания (PDF) - ON Semiconductor
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NCP4623 Datasheet PDF : 20 Pages
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NCP4623
APPLICATION INFORMATION
A typical application circuits for NCP4623 series is
shown in Figure 49.
VIN
C1
100n
NCP4623x
VIN
VOUT
CE
GND
VOUT
C2
100n
VIN
C1
100n
NCP4623xADJ
VIN
VOUT
CE
ADJ
GND
VOUT
R1
C2
100n
R2
Figure 49. Typical Application Schematics
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 NCP4623. Higher values and lower ESR improves line
transient response.
Output Decoupling Capacitor (C2)
Recommended values of the ceramic output decoupling
capacitor is in the range from 0.1 mF to 2.2 mF. Stable
operation of the regulator should be achieved within this
range. 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.
Output Voltage Setting (ADJ version)
The output voltage of the adjustable regulator may be set
for any output voltage from its voltage reference (2.5 V) up
to VIN voltage by an external voltage divider connected
between VOUT and GND pins with its center connected to
the ADJ pin. The voltage divider is loaded by current into
ADJ pin that is typically around 200 nA. This current may
cause an error in VOUT, therefore it is good to choose values
of voltage divider low enough to achieve cross current
around 2 mA to eliminate error. Output voltage can be
computed from the equation:
ǒ Ǔ VOUT + 2.5
1 ) R1
R2
) R1 @ IADJ
(eq. 1)
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. Do not leave the CE pin
unconnected or between VCEH and VCEL voltage levels as
this may leave the output voltage unstable or cause indefinite
and unexpected currents flows internally.
Current Limit
This regulator includes a fold−back type current limit
circuit. This type of protection doesn’t limit output current
up to specified current capability in normal operation, but
when an over current occurs, output voltage and current
decrease until the over current condition ends. Typical
characteristics of this protection type can be observed in the
Output Voltage vs. Output Current graphs shown in the
typical characteristics section of this datasheet.
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.
The IC includes internal thermal shutdown circuit that
stops operation of regulator, if junction temperature is
higher than 150°C. After that, when junction temperature
decreases below 125°C, the operation of voltage regulator
will resume. During high power dissipation condition, the
regulator shuts down and resumes repeatedly protecting
itself from overheating.
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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