NCP508
http://onsemi.com
12
DEFINITIONS
Load Regulation
The change in output voltage for a change in output
current at a constant temperature.
Dropout Voltage
The input/output differential at which the regulator output
no longer maintains regulation against further reductions in
input voltage. Measured when the output drops 100 mV
below its nominal. The junction temperature, load current,
and minimum input supply requirements affect the dropout
level.
Maximum Power Dissipation
The maximum total dissipation for which the regulator
will operate within its specifications.
Quiescent Current
The quiescent current is the current which flows through
the ground when the LDO operates without a load on its
output: internal IC operation, bias, etc. When the LDO
becomes loaded, this term is called the Ground current. It is
actually the difference between the input current (measured
through the LDO input pin) and the output current.
Line Regulation
The change in output voltage for a change in input voltage.
The measurement is made under conditions of low
dissipation or by using pulse technique such that the average
chip temperature is not significantly affected.
Line Transient Response
Typical over and undershoot response when input voltage
is excited with a given slope.
Thermal Protection
Internal thermal shutdown circuitry is provided to protect
the integrated circuit in the event that the maximum junction
temperature is exceeded. When activated at typically 125°C,
the regulator turns off. This feature is provided to prevent
failures from accidental overheating.
Maximum Package Power Dissipation
The maximum power package dissipation is the power
dissipation level at which the junction temperature reaches
its maximum operating value, i.e. 150°C. Depending on the
ambient power dissipation and thus the maximum available
output current.
APPLICATIONS INFORMATION
Typical application circuit for the NCP508 series is shown
in Figure 1.
Input Decoupling (C1)
An input capacitor of at least 1.0 mF,(ceramic or tantalum)
is recommended to improve the transient response of the
regulator and/or if the regulator is located more than a few
inches from the power source. It will also reduce the circuit’s
sensitivity to the input line impedance at high frequencies.
The capacitor should be mounted with the shortest possible
track length directly across the regular’s input terminals.
Higher values and lower ESR will improve the overall line
transient response.
Output Decoupling (C2)
The NCP508 is a stable regulator and does not require a
minimum output current. Capacitors exhibiting ESRs
ranging from a few mW up to 3 W can safely be used. The
minimum decoupling value is 1.0 mF and can be augmented
to fulfill stringent load transient requirements. The regulator
accepts ceramic chip capacitors as well as tantalum devices.
Larger values improve noise rejection and load regulation
transient response.
Enable Operation
The enable pin will turn on or off the regulator. The limits
of threshold are covered in the electrical specification
section of this datasheet. If the enable is not used then the pin
should be connected to V
in
.
Hints
Please be sure the V
in
and GND lines are sufficiently wide.
When the impedance of these lines is high, there is a chance
to pick up noise or cause the regulator to malfunction.
Set external components, especially the output capacitor,
as close as possible to the circuit, and make leads as short as
possible.
Thermal Considerations
Internal thermal limiting circuitry is provided to protect
the integrated circuit in the event that the maximum junction
temperature is exceeded.
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 effect the rate of temperature rise for
the part. This is stating that when the NCP508 has good
thermal conductivity through the PCB, the junction
temperature will be relatively low with high power
dissipation applications.
The maximum dissipation the package can handle is given
by:
(eq. 1)
P
D
+
T
J
(
max
)
* T
A
R
qJA
where:
− T
J{max)
is the maximum allowable junction temperature
of the die, which is 150°C
− T
A
is the ambient operating temperature
− R
q
ja
is dependent on the surrounding PCB layout
