ncp1117lp ON Semiconductor, ncp1117lp Datasheet - Page 9

• Manufacturer Part Number: ncp1117lp
• Description: 1.0 A Low-dropout Positive Fixed And Adjustable Voltage Regulators
• Manufacturer: ON Semiconductor

Protection Diodes
diode paths that normally do not require protection when
used in the typical regulator applications. The first path
connects between V
surge current of about 15 A. Normal cycling of V
generate a current surge of this magnitude. Only when V
is shorted or crowbarred to ground and C
50 mF, it becomes possible for device damage to occur.
Under these conditions, diode D1 is required to protect the
device. The second path connects between C
it can withstand a peak surge current of about 150 mA.
Protection diode D2 is required if the output is shorted or
crowbarred to ground and C
required in the event that V
is greater than 50 mF. The peak current capability stated for
the internal diodes are for a time of 100 ms with a junction
temperature of 25°C. These values may vary and are to be
used as a general guide.
Load Regulation
load regulation; but since these are three terminal devices,
only partial remote load sensing is possible. There are two
conditions that must be met to achieve the maximum
available load regulation performance. The first is that the
top side of programming resistor R1 should be connected as
close to the regulator case as practicable. This will minimize
the voltage drop caused by wiring resistance RW + from
appearing in series with reference voltage that is across R1.
The second condition is that the ground end of R2 should be
connected directly to the load. This allows true Kelvin
sensing where the regulator compensates for the voltage
drop caused by wiring resistance RW −.
The NCP1117LP family has two internal low impedance
A combination of protection diodes D1 and D2 may be
The NCP1117LP series is capable of providing excellent
Input
C
in
Figure 22. Protection Diode Placement
+
3
NCP1117LP
out
D1
and V
1
R2
in
adj
in
2
is shorted to ground and C
, and it can withstand a peak
is greater than 1.0 mF.
+
R1
C
adj
D2
out
adj
is greater than
and V
in
Output
+
out
C
http://onsemi.com
cannot
out
, and
adj
in
9
Thermal Considerations
that is designed to protect the regulator in the event that the
maximum junction temperature is exceeded. When
activated, typically at 165°C, the regulator output switches
off and then back on as the die cools. As a result, if the device
is continuously operated in an overheated condition, the
output will appear to be oscillating. This feature provides
protection from a catastrophic device failure due to
accidental overheating. It is not intended to be used as a
substitute for proper heatsinking. The maximum device
power dissipation can be calculated by:
package. This package has an exposed metal tab that is
specifically designed to reduce the junction to air thermal
resistance, R
copper as a heat dissipater. Figure 19 shows typical R
values that can be obtained from a square pattern using
economical single sided 1.0 oz and 2.0 oz copper board
material. The final product thermal limits should be tested
and quantified in order to insure acceptable performance and
reliability. The actual R
graphs shown. This will be due to any changes made in the
copper aspect ratio of the final layout, adjacent heat sources,
and air flow.
Input
This series contains an internal thermal limiting circuit
The devices are available in surface mount SOT−223
C
Input
in
mF
10
Figure 24. Constant Current Regulator
+
3
NCP1117LP
3
+
qJA
NCP1117LP
Figure 23. Load Sensing
, by utilizing the printed circuit board
P D +
1
I out +
1
qJA
T J(max) * T A
2
can vary considerably from the
V ref
R
R1
2
R qJA
R2
) I adj
R
+
C
Constant Current
out
RW+
RW−
+
10
mF
Output
Output
Remote
Load
qJA