NCP551, NCV551
www.onsemi.com
9
APPLICATIONS INFORMATION
A typical application circuit for the NCP551 series is
shown in Figure 20.
Input Decoupling (C1)
A 0.1 mF capacitor either ceramic or tantalum is
recommended and should be connected close to the NCP551
package. Higher values and lower ESR will improve the
overall line transient response.
Output Decoupling (C2)
The NCP551 is a stable Regulator and does not require
any specific Equivalent Series Resistance (ESR) or a
minimum output current. Capacitors exhibiting ESRs
ranging from a few mW up to 3.0 W can thus safely be used.
The minimum decoupling value is 0.1 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. These
limits of threshold are covered in the electrical specification
section of this data sheet. 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
As power across the NCP551 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 effect the rate of temperature rise for the part.
This is stating that when the NCP551 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:
PD +
T
J(max)
* T
A
R
qJA
If junction temperature is not allowed above the
maximum 125°C, then the NCP551 can dissipate up to
400 mW @ 25°C.
The power dissipated by the NCP551 can be calculated
from the following equation:
P
tot
+
ƪ
V
in
*I
gnd
(I
out
)
ƫ
)
[
V
in
* V
out
]
*I
out
or
V
inMAX
+
P
tot
)
V
out
*
I
out
I
GND
) I
out
If a 150 mA output current is needed then the ground
current from the data sheet is 4.0 mA. For an
NCP551SN30T1 (3.0 V), the maximum input voltage will
then be 5.6 V.
Battery or
Unregulated
Voltage
Figure 20. Typical Application Circuit
V
out
C1
C2
OFF
ON
+
+
1
3
2
4
5
