ETC RC2951M-3.3

www.fairchildsemi.com
RC2951
Adjustable Micropower Voltage Regulator
Features
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 supplying output currents in excess of 100mA. It has internal current 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.
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
8 lead SOIC package
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
VOUT
IL ≤ 100 mA
Unregulated DC
+
7
8
1
FeedBack
Input
Output
2
+
Sense
–
From
CMOS
or TTL
Error
Amplifier
3
Shut
Down
6
+
See Application
Discussion
VTAP
5
330kΩ
+
+
60 mV
+
–
1.23V
Reference
To CMOS
or TTL
Error
4
Ground
Error Detection Comparator
PRELIMINARY INFORMATION describes products that are not in full production at the time of printing. Specifications are based on design goals
REV. 1.0.0 2/8/01
and limited characterization. They may change without notice. Contact Raytheon for current information.
RC2951
PRODUCT SPECIFICATION
Pin Assignments
8 Lead SOIC Package
Output
1
8
Input
Sense
2
7
Feedback
Shutdown
3
6
VTAP
Ground
4
5
Error
Top View
Absolute Maximum Ratings
Power Dissipation
Internally Limited
Lead Temp. (Soldering, 5 seconds)
260°C
Storage Temperature Range
–65° to +150°C
1
Operating Junction Temperature Range
–55° to +150°C
Input Supply/Voltage
–0.3 to +30V
Feedback Input Voltage2,3
–1.5 to +30V
Shutdown Input Voltage2
–0.3 to +30V
Error Comparator Output
Voltage2
–0.3 to +30V
Notes:
1. Junction to ambient thermal resistance for the S.O. (M) package is 160°C/W.
2 May exceed input supply voltage.
3. When used in dual-supply systems where the output terminal sees loads returned to a negative supply, the output voltage
should be diode-clamped to ground.
Electrical Characteristics
The • denotes that the limits apply at temperature extremes.
Parameter
Conditions1
Typ.
Tested Limit2
Units
Output Voltage
(RC2951M)
TJ = 25°C
5.0
5.025
4.975
V max
V min
-25°C ≤ TJ ≤ 85°C
5.0
V max
V min
Full Operating Temperature
Range
•
•
5.0
5.06
4.94
V max
V min
Output Voltage
(RC2951M)
100µA ≤ IL ≤ 100mA
TJ ≤ TJMAX
•
•
5.0
5.075
4.925
V max
V min
Output Voltage
(RC2951M-3.3)
TJ = 25°C
3.3
3.317
3.284
V max
V min
-25°C ≤ TJ ≤ 85°C
3.3
Output Voltage
(RC2951M-3.3)
Output Voltage Temperature
Coefficient7
2
V max
V min
Full Operating Temperature
Range
•
•
3.3
3.340
3.260
V max
V min
100µA ≤ IL ≤ 100mA
TJ ≤ TJMAX
•
•
3.3
3.346
3.254
V max
V min
•
20
120
ppm/°C
REV. 1.0.0 2/8/01
PRODUCT SPECIFICATION
RC2951
Electrical Characteristics (continued)
The • denotes that the limits apply at temperature extremes.
Parameter
Line
Regulation9, 10
Load
Regulation9
Dropout Voltage3
Conditions1
Typ.
Tested Limit2
Units
(VONOM + 1)V ≤ Vin ≤ 20V
0.03
0.1
0.5
% max
% max
0.08
0.2
0.4
% max
% max
50
80
150
mV max
mV max
380
500
700
mV max
mV max
75
120
140
µA max
µA max
8
14
15
mA max
mA max
110
250
300
µA max
µA max
160
200
220
mA max
mA max
0.05
0.2
%/W max
100 µA ≤ IL ≤ 100 mA
IL = 100 µA
IL = 100 mA
Ground Current
IL = 100 µA
IL = 100 mA
Dropout Ground Current
Vin = (VONOM - 0.5)V
IL = 100 µA
Current Limit
Vout = 0
•
•
•
•
•
•
•
•
Thermal Regulation8
Output Noise,
10 Hz to
100 KHz
CL = 1 µF (5V Only)
430
µV rms
CL = 200 µF
160
µV rms
CL = 3.3 µF
(Bypass = 0.01 µF
Pins 7 to 1 (RC2951)
100
µV rms
Reference Voltage
•
1.25
1.26
1.22
1.2
V max
V max
V min
V min
•
•
1.27
1.19
V max
V min
40
60
nA max
nA max
•
Reference Voltage5
Feedback Pin Bias Current
•
1.235
20
Reference Voltage
Temperature Coefficient7
20
ppm/°C
Feedback Pin Bias Current
Temperature Coefficient
0.1
nA/°C
Error Comparator
Output Leakage Current
VOH = 30V
Output Low Voltage
Vin = (VONOM - 0.5)V
IOL = 400 µA
Upper Threshold Voltage4
Lower Threshold Voltage4
Hysteresis4
REV. 1.0.0 2/8/01
•
•
•
•
0.01
1
2
µA max
µA max
150
250
400
mV max
mV max
60
40
25
mV min
mV min
75
95
140
mV max
mV max
15
mV
3
RC2951
PRODUCT SPECIFICATION
Electrical Characteristics (continued)
The • denotes that the limits apply at temperature extremes.
Parameter
Conditions1
Tested Limit2
Units
0.6
2.0
V
V max
V min
30
50
100
µA max
µA max
450
600
750
µA max
µA max
3
10
20
µA max
µA max
Typ.
Shutdown Input
Input Logic Voltage
Low (Regulator ON)
High (Regulator OFF)
Shutdown Pin Input Current
Vshutdown = 2.4V
Vshutdown = 30V
Regulator Output
Current in Shutdown6
•
•
•
•
•
1.3
Notes:
1. Unless otherwise specified all limits guaranteed for TJ - 25°C, Vin = (VONOM + 1)V, IL = 100µA and CL = 1 µF for 5V
versions, and 2.2 µF for 3V and 3.3V versions. Additional conditions for the 8-pin versions are Feedback tied to VTAP,
Output tied to Output Sense and Vshutdown < 0.8V.
2. Guaranteed and 100% production tested.
3. Dropout Voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value
measured at 1V differential. At very low values of programmed output voltage, the minimum input supply voltage of 2V (2.3V
over temperature) must be taken into account.
4. Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal
reference voltage measured at Vin = (VONOM + 1)V. To express these thresholds in terms of output voltage change, multiply
by the error amplifier gain = Vout/Vref = (R1 + R2)/R2. For example, at a programmed output voltage of 5V, the Error output
is guaranteed to go low when the output drops by 95 mV x 5V/1.235V = 384 mV. Thresholds remain constant as a percent
of Vout as Vout is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.
5. Vref < Vout ≤ (Vin – 1V), 2.3V ≤ Vin ≤ 30V, 100µA ≤ IL ≤ 100 mA, TJ ≤ TJMAX.
6. Vshutdown ≥ 2V, Vin ≤ 30V, Vout = 0, Feedback pin tied to VTAP.
7. Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total
temperature range.
8. Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load or line regulation effects. Specifications are for a 50 mA load pulse at VIN = 30V (1.25W pulse) for
T = 10 ms.
9. Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage
due to heating effects are covered under the specification for thermal regulation.
10. Line regulation for the RC2951 is tested at 150°C for IL = 1 mA. For IL = 100 µA and TJ = 125°C, line regulation is guaranteed
by design to 0.2%. See Typical Performance Characteristics for line regulation versus temperature and load current.
4
REV. 1.0.0 2/8/01
PRODUCT SPECIFICATION
RC2951
Applications Discussion
The RC2951 regulator is designed with internal current limiting and thermal shutdown. It is not internally compensated
and requires a 1.0µF (or greater) capacitor between the output terminal and ground for stability. At lower output voltages, 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 capacitors will perform adequately. Solid tantalums or appropriate
multilayer ceramic capacitors are suggested for operation
below 25°C. At lower values of output current, less capacitance 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 capacitance 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.
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.
4.75V
Output
Voltage
Error*
5V
Input
Voltage
1.3V
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 approximately 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.
REV. 1.0.0 2/8/01
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 depending 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 condition. 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.
5
RC2951
PRODUCT SPECIFICATION
.
+VIN
100K
5
Error
Output
8
+VIN
ERROR
VOUT
VOUT
1.2 30V
1
RC2951
**Shutdown 3
SD
Input
GND
FB
4
7
R1
+
+
3.3µF
.01
µF
R1
V OUT = V REF  1 + ------

R 
2
1.23V
R2
VREF
2950-11
** Drive with TTL-high to shut down. Ground or leave open if shutdown feature is not to be used.
Figure 2. Adjustable Regulator
The complete equation for the output voltage is
V OUT
R1
= V REF •  1 + ------ + I FB R 1

R 
2
V REF
V OUT
-------------- = ------------------R2
R1 + R2
V OUT
R1 + R2
= V REF  -------------------
 R2 
V OUT
R1
= V REF  1 + ------

R 
Reducing Output Noise
In reference applications it may be advantageous to reduce
the AC noise present at the output. One method is to reduce
the regulator bandwidth by increasing the size of the output
capacitor.
Noise can be reduced fourfold by a bypass capacitor across
R1, since it reduces the high frequency gain from 4 to unity.
Pick
1
C BYPASS ≅ -----------------------------------2πR 1 • 200Hz
2
Adding the error term,
R1
V OUT = V REF  1 + ------ + I FB R 2

R 2
or about 0.01 µF. When doing this, the output capacitor must
be increased to 3.3 µF to maintain stability. These changes
reduce the output noise from 430 µV to 100 µV rms for a
100 kHz bandwidth at 5V output. With the bypass capacitor
added, noise no longer scales with output voltage so that
improvements are more dramatic at higher output voltages.
where VREF is the nominal 1.235 reference voltage and IFB
is the feedback pin bias current, nominally -20 nA. The
minimum recommended load current of 1 µA forces an
upper limit of 1.2 MΩ on the value of R2, if the regulator
must work with no load (a condition often found in CMOS in
standby). IFB will produce a 2% typical error in VOUT which
may be eliminated at room temperature by trimming R1.
For better accuracy, choosing R2 = 100k reduces this error
to 0.17% while increasing the resistor program current to
12 µA. Since the RC2951 typically draws 60 µA at no load
with Pin 2 open-circuited, this is a small price to pay.
6
REV. 1.0.0 2/8/01
PRODUCT SPECIFICATION
RC2951
Typical Applications
Unregulated
Input
1µF
0.01µF
10kΩ
Supertex
VP12C
8
6
IN
VTAP
Output
5V±1%@
0 to 1A
2
SENSE
+
220µF
RC2951
7
FB
OUT
GND
4
1MΩ
1
2kΩ
0.002µF
IQ艑400µA
Figure 3. 1A Regulator with 1.2V Dropout
Unregulated
Input
+VIN
8
OUT
IN
1
330Ω
2N5432
(2)
27kΩ
8
+VIN
RC2951
6
Error
Output
SENSE
VTAP
FB
7
GND
4
2
5V
Output
ERROR
VOUT
1 *VOUT≈VIN
RC2951
**Shutdown 3
SD
Input
GND
Load
50mA to
300mA
+
4.7µF
5
4
FB
4
Figure 4. 300 mA Regulator with 0.75 Dropout
*Minimum input-output voltage ranges from
40 mV to 400 mV, depending on load current.
Current limit is typically 160 mA.
+V = 2
30V
Load
IL
Figure 5. Wide Input Voltage Range
Current Limiter
IL=
1.23
R
8
VIN
VOUT
1
RC2951
Shutdown 3
SD
Input
0.1µF
GND
FB
4
7
R
1%
1 µF
+
2950-12
Figure 6. Low Drift Current Source
REV. 1.0.0 2/8/01
7
RC2951
PRODUCT SPECIFICATION
Typical Applications (continued)
+VIN
Current
Limit Section
D1
8
2
+VIN
SENSE
6
VOUT
VTAP
5V Memory
Supply
D2
1
+VIN = VOUT +5.0V
680
0.05
470
20
RC2951
#1
5
FB
ERROR
7
MJE2955
+
1µF
2N3906
3.6V
Nicad
GND
+VIN
4
ERROR
3
EARLY WARNING
D3
6
7
3
2
+VIN
SENSE
VOUT
Error
Flag
R1 +
330kΩ
µP
VDD
FB RC2951
#2
5
SD
ERROR
1%
VOUT
+
100
µF
4.7
TANT.
R2
1
.033
47
RESET
Main 5V Output
1
7
FB
4
8
VTAP
SD
GND
220
D4
20kΩ
Q1
5
RC2951
27kΩ
2.7MΩ
+VOUT @ 2A
10kΩ
8
4.7MΩ
(
)
R1
R2
For 5VOUT,use internal resistors. Wire pin 6 to 7, & wire pin 2 +VOUT Buss.
VOUT = 1.23V 1 +
+
Figure 9. 2 Ampere Low Dropout Regulator
1µF
GND
+VIN
4
C-MOS
GATE
*Sleep
Input
• Early warning flag on low input voltage
• Main output latches of f at lower input voltages
• Battery backup on auxillary output
47kΩ
470kΩ
8
Operation Reg. #1’s VOUT is programmed one diode drop above 5V. Its error
flag becomes active when Vin ≤ 5.7V. WhenVin drops below 5.3V, the error
flag of Reg. #2 becomes active and via Q1 latches the main output off.
When Vin again exceeds 5.7V Reg. #1 is back in regulation and the early
warning signal rises unlatching Reg. #2 via D3.
Figure 7. Regulator with Early Warning and Auxillary Output
+VIN
Error
Output
5
ERROR
VOUT
+VOUT
1
100
pF
RC2951
Shutdown 3
SD
Input
GND
200kΩ
+ 3.3µF
1%
2N3906
FB
4
100kΩ
7
1%
100kΩ
+VIN
*High input lowers VOUT to 2.5V.
8
470kΩ
Figure 10. 5V Regulator with 2.5V Sleep Function
+VIN
5
VOUT
1
ERROR
VOUT
470kΩ
R1
RC2951
3
Reset
SD
FB
GND
7
+5V
+
1µF
4
4.7kΩ
20mA
Output*
8
R2
1
VIN
4
1N
4001
VOUT
1
RC2951
Figure 8. Latch Off When Error Flag Occurs
FB
0.1µF
5
7
2
GND
4
* High for
IL < 3.5mA
4
1N457
Min. Voltages ≈ 4V
360
2950-13
Figure 11. Open Circuit Detector for 4mA to 20mA Current Loop
8
REV. 1.0.0 2/8/01
PRODUCT SPECIFICATION
RC2951
Typical Applications (continued)
8
39kΩ
RESET
+VIN
5
2
SENSE
ERROR
+VOUT = 5V
1
VOUT
+
RC2951
–
*C4
+
3
SD
GND
VTAP
4
6
39kΩ
6V
Lead-Acid
Battery
+
1%
1%
C1-C4
LP339
1%
100
kΩ
1kΩ
1kΩ
1µF
7
FB
–
C1
+
100kΩ
–
C2
+
100kΩ
–
C3
+
100kΩ
< 5.8V**
< 6.0V**
< 6.2V**
10kΩ
R3
1%
20kΩ
*Optional Latch off when drop out occurs. Adjust R3 for C2 Switching when Vin is 6.0V.
**Outputs go low whenVin drops below designated thresholds.
Figure 12. Regulator with State-of-Charge Indicator
For values shown, Regulator shuts down when Vin < 5.5V and turns on again at 6.0V. Current drain in disconnected mode is ≈ 150 µA.
+
6V
Sealed
Lead-Acid
Battery
Source
120kΩ
1.5kΩ**
+
FB
8
1N457
+VIN
LM385
≈ 400kΩ*
for 5.5V
100kΩ
1
Main V+
2
Memory V+
VOUT
–
RC2951
3
SENSE
SD
GND
4
FB
VTAP
7
20Ω
+
6
1µF
+
Ni-cad
Backup
Battery
*Sets disconnect Voltage
**Sets disconnect Hysteresis
2950-14
Figure 13. Low Battery Disconnect
REV. 1.0.0 2/8/01
9
RC2951
PRODUCT SPECIFICATION
Mechanical Dimensions – 8 Lead SOIC
Inches
Symbol
Min.
A
A1
B
C
D
E
e
H
h
L
N
α
ccc
Millimeters
Max.
Min.
Max.
.053
.069
.004
.010
.013
.020
.008
.010
.189
.197
.150
.158
.050 BSC
1.35
1.75
0.10
0.25
0.33
0.51
0.20
0.25
4.80
5.00
3.81
4.01
1.27 BSC
.228
.010
.016
5.79
0.25
0.40
.244
.020
.050
8
6.20
0.50
1.27
8
0°
8°
0°
8°
—
.004
—
0.10
8
Notes:
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
2. "D" and "E" do not include mold flash. Mold flash or
protrusions shall not exceed .010 inch (0.25mm).
3. "L" is the length of terminal for soldering to a substrate.
4. Terminal numbers are shown for reference only.
5
2
2
5. "C" dimension does not include solder finish thickness.
6. Symbol "N" is the maximum number of terminals.
3
6
5
E
1
H
4
h x 45°
D
C
A1
A
α
SEATING
PLANE
e
B
10
–C–
LEAD COPLANARITY
L
ccc C
REV. 1.0.0 2/8/01
RC2951
PRODUCT SPECIFICATION
Ordering Information
Product Number
Package
RC2951M
8 pin SOIC
RC2951M-3.3
8 pin SOIC
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
2/8/01 0.0m 001
Stock#DS30002951
 2001 Fairchild Semiconductor Corporation