NCV1117 ON Semiconductor, NCV1117 Datasheet - Page 8

• Manufacturer Part Number: NCV1117
• Description: 1.0 A Low−dropout Positive Fixed and Adjustable Voltage Regulators
• Manufacturer: ON Semiconductor

Introduction
voltage along with enhanced output voltage accuracy and
temperature stability when compared to older industry
standard three−terminal adjustable regulators. These
devices contain output current limiting, safe operating area
compensation and thermal shutdown protection making
them designer friendly for powering numerous consumer
and industrial products. The NCP1117 series is pin
compatible with the older LM317 and its derivative device
types.
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
depending upon the output voltage.
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 NCP1117 features a significant reduction in dropout
The typical application circuits for the fixed and
Input bypass capacitor C
Figure 20. Fixed Output Regulator
Input
C
in
gnd
+
3
, ranges from 3.0 mA to 5.0 mA
NCP1117
XTXX
in
1
may be required for regulator
I
gnd
2
+
C
Output
out
APPLICATIONS INFORMATION
NCP1117, NCV1117
http://onsemi.com
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
0.25 W to 2.2 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 12 V
regulator, the output ripple will increase by 12 V/1.25 V or
9.6 and the ripple rejection will decrease by 20 log of this
ratio or 19.6 dB. The loss of ripple rejection can be restored
to the values shown with the addition of bypass capacitor
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:
is obtainable with the adjust pin properly bypassed.
adj
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
Figures 10 and 11 shows the level of ripple rejection that
f ripple + 120 Hz, R1 + 120 W, then C adj u 11.1 mF
, shown in Figure 21. The reactance of C
Input
Figure 21. Adjustable Output Regulator
C
out
in
V out + V ref 1 ) R2
and its use is mandatory to ensure output
3
+
adj
C adj u
I
adj
NCP1117
is significantly reduced in applications
XTA
1
R2
2 p f ripple R1
R1
2
V
ref
1
) I adj R2
+
R1
C
adj
adj
+
Output
at the ripple
C
out
adj
is: