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PDF RC2951 Data sheet ( Hoja de datos )
| Número de pieza | RC2951 | |
| Descripción | Adjustable Micropower Voltage Regulator | |
| Fabricantes | Fairchild Semiconductor | |
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www.fairchildsemi.com
RC2951
Adjustable Micropower Voltage Regulator
Features
• High accuracy output voltage
• Guaranteed 100 mA output current
• Extremely low quiescent current
• Extremely tight load and line regulation
• Requires only a 1.0µF output capacitor for stability
• Internal Current and Thermal Limiting
• Error flag warns of output dropout
• Logic-controlled electronic shutdown
• Output programmable from 1.24 to 29V
• Fixed 3.3V version available
• -25°C to +85°C operating range
• 8 lead SOIC package
Description
The RC2951 is a voltage regulator specifically designed to
maintain proper regulation with a very low dropout voltage
(Typ. 40mV at light loads and 380 mV at 100mA). It has a
low quiescent bias current of 75µA and is capable of supply-
ing output currents in excess of 100mA. It has internal cur-
rent and thermal limiting protection. The output can be
programmed from 1.24V to 29V with two external resistors.
A fixed output voltage (3.3V) is also available.
The error flag output can be used as power-on reset for
warning of a low output voltage. The Shutdown input feature
allows a logic level signal to turn on and off the regulator
output. The RC2951 is ideally suited for battery powered
computer, consumer, and industrial equipment where an
extension of useful battery life is desirable. The RC2951 is
available in an 8-pin SOIC package.
Block Diagram
Unregulated DC
7
+ Feed-
Back
8
Input
1
Output
From
CMOS
or TTL
3
Shut
Down
+
–
Error
Amplifier
+
+
60 mV
+ 1.23V
–
Reference
Error Detection Comparator
VOUT
IL ≤ 100 mA
2
Sense
6
VTAP
5
Error
4
Ground
+
See Application
Discussion
330kΩ
To CMOS
or TTL
PRELIMINARY INFORMATION describes products that are not in full production at the time of printing. Specifications are baRseEdVo.n1d.0e.s1ig4n/g8o/0al2s
and limited characterization. They may change without notice. Contact Raytheon for current information.
1 page  
PRODUCT SPECIFICATION
RC2951
Applications Discussion
The RC2951 regulator is designed with internal current lim-
iting and thermal shutdown. It is not internally compensated
and requires a 1.0µF (or greater) capacitor between the out-
put terminal and ground for stability. At lower output volt-
ages, more capacitance is required (2.2µF or more is
recommended for 3V and 3.3V versions) for stability. Most
types of aluminum, tantalum or multilayer ceramic capaci-
tors will perform adequately. Solid tantalums or appropriate
multilayer ceramic capacitors are suggested for operation
below 25°C. At lower values of output current, less capaci-
tance is needed to maintain stability at output. The capacitor
at the output can be reduced to 0.33µF for currents less that
10mA, or 0.1µF for currents below 1.0mA.
Using the adjustable versions at voltages below 5V runs the
error amplifier at lower gains so that more output capaci-
tance is needed. For the worst-case situation of a 100 mA
load at 1.23V output (Output shorted to Feedback) a
3.3 µF (or greater) capacitor should be used.
When setting the output voltage of the RC2951 versions with
external resistors, a minimum load of 1 µA is recommended.
A 1 µF tantalum or aluminum electrolytic capacitor should
be placed from the RC2951 input to ground if there is more
than 10 inches of wire between the input and the AC filter
capacitor or if a battery is used as the input.
Stray capacitance to the RC2951 Feedback terminal can
cause instability. This may especially be a problem when
using high value external resistors to set the output voltage.
Adding a 100 pF capacitor between Output and Feedback
and increasing the output capacitor to at least 3.3 µF will fix
this problem.
Error Detection Comparator Output
The comparator switches to a logic low whenever the
RC2951 output falls out of regulation by more than approxi-
mately 5%. This value is the comparator’s built-in offset of
about 60 mV divided by the 1.235 internal reference voltage.
This trip level remains “5% below normal” regardless of the
value of the output voltage. For example, the error flag trip
level is typically 4.75V for a 5V output or 11.4V for a 12V
output. The out of regulation condition may be due either to
low input voltage, current limiting, or thermal limiting.
Figure 1 is a timing diagram showing the ERROR signal and
the regulated output voltage as the RC2951 input is ramped
up and down. For 5V versions, the ERROR signal becomes
valid (low) at about 1.3V input. It goes high at about 5V
input (the input voltage at which VOUT = 4.75.) Since the
RC2951’s dropout voltage is load-dependent (see curve in
typical performance characteristics), the input voltage trip
point (about 5V) will vary with the load current. The output
voltage trip point (approx. 4.75V) does not vary with load.
Output
Voltage
4.75V
Error*
Input
Voltage
5V
1.3V
2950-10
Figure 1. ERROR Output Timing
The error comparator has an open-collector output which
requires an external pullup resistor. This resistor may be
returned to the output or some other supply voltage depend-
ing on system requirements. In determining a value for this
resistor, note that while the output is rated to sink 400 µA,
this sink current adds to battery drain in a low battery condi-
tion. Suggested values range from 100k to 1MΩ. The resistor
is not required if this output is unused.
Programming the Output Voltage (RC2951)
The RC2951 may be pin-strapped for the nominal fixed
output voltage using its internal voltage divider by tying the
output and sense pins together, and also tying the feedback
and VTAP pins together. Alternatively, it may be programmed
for any output voltage between its 1.235V reference and its
30V maximum rating. As seen in Figure 2 an external pair of
resistors is required.
REV. 1.0.1 4/8/02
5
5 Page 
RC2951
Ordering Information
Product Number
RC2951MT
RC2951M33
Package
8-pin SOIC in tape and reel
8-pin SOIC
PRODUCT SPECIFICATION
DISCLAIMER
FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO
ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME
ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN;
NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
LIFE SUPPORT POLICY
FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, and (c) whose failure to
perform when properly used in accordance with
instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
user.
2. A critical component in any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
www.fairchildsemi.com
4/8/02 0.0m 001
Stock#DS30002951
2001 Fairchild Semiconductor Corporation
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet RC2951.PDF ] | |
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