ncp1117lp ON Semiconductor, ncp1117lp Datasheet - Page 8

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

Introduction
adjustable mode regulator with 1 A output capability. This
LDO is guaranteed to have a significant reduction in dropout
voltage along with enhanced output voltage accuracy and
temperature stability when compared to older industry
standard three−terminal adjustable regulators.
area compensation and thermal shutdown protection
making them designer friendly for powering numerous
consumer and industrial products. The NCP1117LP series is
pin compatible with the older NCP1117.
Output Voltage
adjustable output regulators are shown in Figures 20 and 21.
The adjustable devices are floating voltage regulators. They
develop and maintain the nominal 1.25 V reference voltage
between the output and adjust pins. The reference voltage is
programmed to a constant current source by resistor R1, and
this current flows through R2 to ground to set the output
voltage. The programmed current level is usually selected to
be greater than the specified 5.0 mA minimum that is
required for regulation. Since the adjust pin current, I
significantly lower and constant with respect to the
programmed load current, it generates a small output
voltage error that can usually be ignored. For the fixed
output devices R1 and R2 are included within the device and
the ground current I
External Capacitors
stability if the device is located more than a few inches from
the power source. This capacitor will reduce the circuit’s
sensitivity when powered from a complex source
impedance and significantly enhance the output transient
response. The input bypass capacitor should be mounted
with the shortest possible track length directly across the
regulator’s input and ground terminals. A 10 mF ceramic or
tantalum capacitor should be adequate for most
applications.
The NCP1117LP is a low dropout positive fixed or
These devices contain output current limiting, safe operating
The typical application circuits for the fixed and
Input bypass capacitor C
Input
Figure 20. Fixed Output Regulator
C
in
+
3
gnd
NCP1117LP
is 550 mA (typ).
1
in
I
may be required for regulator
gnd
2
+
C
Output
out
APPLICATIONS INFORMATION
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adj
, is
8
capacitor C
stability. A minimum capacitance value of 4.7 mF with an
equivalent series resistance (ESR) that is within the limits of
20 mW to 20 W is required. The capacitor type can be
ceramic, tantalum, or aluminum electrolytic as long as it
meets the minimum capacitance value and ESR limits over
the circuit’s entire operating temperature range. Higher
values of output capacitance can be used to enhance loop
stability and transient response with the additional benefit of
reducing output noise.
adjustable devices as the ratio of output voltage to the
reference voltage increases. For example, with a 5 V
regulator, the output ripple will increase by 5 V/1.25 V or 4
and the ripple rejection will decrease by 20 log of this ratio
or 12 dB. The loss of ripple rejection can be restored to the
values shown with the addition of bypass capacitor C
shown in Figure 21. The reactance of C
frequency must be less than the resistance of R1. The value
of R1 can be selected to provide the minimum required load
current to maintain regulation and is usually in the range of
100 W to 200 W.
from the above formula. When using the device in an
application that is powered from the AC line via a
transformer and a full wave bridge, the value for C
where the input ripple frequency is high. If used as a post
regulator in a switching converter under the following
conditions:
f ripple + 50 kHz, R1 + 120 W, then C adj u 0.027 mF
Frequency compensation for the regulator is provided by
The output ripple will increase linearly for fixed and
The minimum required capacitance can be calculated
The value for C
f ripple + 120 Hz, R1 + 120 W, then C adj u 11.1 mF
Input
C
Figure 21. Adjustable Output Regulator
in
out
3
+
V out + V ref 1 ) R2
I
and its use is mandatory to ensure output
adj
NCP1117LP
C adj u
adj
is significantly reduced in applications
1
R2
2p @ f ripple @ R1
2
V
R1
ref
1
) R2 @ I adj
+
R1
C
adj
adj
Output
+
C
at the ripple
out
adj
is:
adj
,