RC2951M-3.3 [ETC]
Fixed & Adjustable Voltage Regulator ; 固定和可调电压稳压器\n
| 型号： | RC2951M-3.3 |
| 厂家： | 
ETC |
| 描述： | Fixed & Adjustable Voltage Regulator
|
| 文件： | 总11页 (文件大小：215K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
www.fairchildsemi.com
RC2951
Adjustable Micropower Voltage Regulator
Features
Description
• High accuracy output voltage
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.
• 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
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.
• 8 lead SOIC package
Block Diagram
V
OUT
Unregulated DC
I
≤ 100 mA
L
7
8
1
+
Feed-
Back
Input
Output
2
+
Sense
–
6
5
Error
Amplifier
+
3
From
CMOS
or TTL
See Application
Discussion
V
TAP
Shut
Down
330kΩ
+
+
–
To CMOS
or TTL
60 mV
Error
+
1.23V
Reference
4
Ground
Error Detection Comparator
REV. 1.0.0 2/8/01
RC2951
PRODUCT SPECIFICATION
Pin Assignments
8 Lead SOIC Package
Input
Output
8
7
6
5
1
2
3
4
Feedback
VTAP
Sense
Shutdown
Ground
Error
Top View
Absolute Maximum Ratings
Power Dissipation
Internally Limited
260°C
Lead Temp. (Soldering, 5 seconds)
Storage Temperature Range
Operating Junction Temperature Range1
Input Supply/Voltage
Feedback Input Voltage2,3
Shutdown Input Voltage2
Error Comparator Output Voltage2
Notes:
–65° to +150°C
–55° to +150°C
–0.3 to +30V
–1.5 to +30V
–0.3 to +30V
–0.3 to +30V
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
5.0
5.0
3.3
3.3
3.3
3.3
20
V max
V min
Full Operating Temperature
Range
•
•
5.06
4.94
V max
V min
Output Voltage
(RC2951M)
100µA ≤ IL ≤ 100mA
TJ ≤ TJMAX
•
•
5.075
4.925
V max
V min
Output Voltage
(RC2951M-3.3)
TJ = 25°C
3.317
3.284
V max
V min
-25°C ≤ TJ ≤ 85°C
V max
V min
Full Operating Temperature
Range
•
•
3.340
3.260
V max
V min
Output Voltage
(RC2951M-3.3)
100µA ≤ IL ≤ 100mA
TJ ≤ TJMAX
•
•
3.346
3.254
V max
V min
Output Voltage Temperature
Coefficient7
•
120
ppm/°C
2
REV. 1.0.0 2/8/01
PRODUCT SPECIFICATION
RC2951
Electrical Characteristics (continued)
The • denotes that the limits apply at temperature extremes.
Parameter
Conditions1
Typ.
Tested Limit2
Units
Line Regulation9, 10
(VONOM + 1)V ≤ Vin ≤ 20V
0.03
0.1
0.5
% max
% max
•
•
•
•
•
•
•
•
Load Regulation9
Dropout Voltage3
100 µA ≤ IL ≤ 100 mA
IL = 100 µA
0.08
50
0.2
0.4
% max
% max
80
150
mV max
mV max
IL = 100 mA
380
75
500
700
mV max
mV max
Ground Current
IL = 100 µA
120
140
µA max
µA max
IL = 100 mA
8
14
15
mA max
mA max
Dropout Ground Current
Current Limit
Vin = (VONOM - 0.5)V
IL = 100 µA
110
160
250
300
µA max
µA max
Vout = 0
200
220
mA max
mA max
Thermal Regulation8
0.05
430
160
100
0.2
%/W max
µV rms
µV rms
µV rms
Output Noise,
10 Hz to
100 KHz
CL = 1 µF (5V Only)
CL = 200 µF
CL = 3.3 µF
(Bypass = 0.01 µF
Pins 7 to 1 (RC2951)
Reference Voltage
1.235
1.25
1.26
1.22
1.2
V max
V max
V min
V min
•
•
Reference Voltage5
•
•
1.27
1.19
V max
V min
Feedback Pin Bias Current
20
20
40
60
nA max
nA max
•
Reference Voltage
ppm/°C
Temperature Coefficient7
Feedback Pin Bias Current
Temperature Coefficient
0.1
nA/°C
Error Comparator
Output Leakage Current
VOH = 30V
0.01
150
60
1
2
µA max
µA max
•
•
•
•
Output Low Voltage
Upper Threshold Voltage4
Lower Threshold Voltage4
Hysteresis4
Vin = (VONOM - 0.5)V
IOL = 400 µA
250
400
mV max
mV max
40
25
mV min
mV min
75
95
140
mV max
mV max
15
mV
REV. 1.0.0 2/8/01
3
RC2951
PRODUCT SPECIFICATION
Electrical Characteristics (continued)
The • denotes that the limits apply at temperature extremes.
Parameter
Conditions1
Typ.
Tested Limit2
Units
Shutdown Input
Input Logic Voltage
1.3
V
Low (Regulator ON)
High (Regulator OFF)
•
•
0.6
2.0
V max
V min
Shutdown Pin Input Current
V
shutdown = 2.4V
30
450
3
50
100
µA max
µA max
•
•
•
Vshutdown = 30V
600
750
µA max
µA max
Regulator Output
10
20
µA max
µA max
Current in Shutdown6
Notes:
1. Unless otherwise specified all limits guaranteed for T - 25°C, V = (V NOM + 1)V, I = 100µA and C = 1 µF for 5V
J
in
O
L
L
versions, and 2.2 µF for 3V and 3.3V versions. Additional conditions for the 8-pin versions are Feedback tied to V
,
TAP
Output tied to Output Sense and V
< 0.8V.
shutdown
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 V = (V NOM + 1)V. To express these thresholds in terms of output voltage change, multiply
in
O
by the error amplifier gain = V /V = (R1 + R2)/R2. For example, at a programmed output voltage of 5V, the Error output
out ref
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 V as V is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.
out
out
5. V < V ≤ (V – 1V), 2.3V ≤ V ≤ 30V, 100µA ≤ I ≤ 100 mA, T ≤ T .
JMAX
ref
out
in
in
L
J
6. V
≥ 2V, V ≤ 30V, V = 0, Feedback pin tied to V
.
shutdown
in
out
TAP
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, ex-
cluding load or line regulation effects. Specifications are for a 50 mA load pulse at V = 30V (1.25W pulse) for
IN
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 I = 1 mA. For I = 100 µA and T = 125°C, line regulation is guaranteed
L
L
J
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 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.
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*
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.
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.
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.
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.
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.
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.
REV. 1.0.0 2/8/01
5
RC2951
PRODUCT SPECIFICATION
.
+VIN
100K
5
8
VOUT
+VIN
1.2 30V
1
Error
Output
VOUT
ERROR
RC2951
R1
+
+
VOUT = VREF 1 + ------
R2
3
**Shutdown
Input
R1
3.3µF
SD
GND
.01
µF
FB
4
7
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
R1
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.
VOUT = VREF • 1 + ------ + IFBR1
R2
VREF
VOUT
------------- = -------------------
R2
R1 + R2
Noise can be reduced fourfold by a bypass capacitor across
R1, since it reduces the high frequency gain from 4 to unity.
Pick
R1 + R2
-------------------
R2
VOUT = VREF
1
-----------------------------------
CBYPASS
R1
2πR1 • 200Hz
VOUT = VREF 1 + ------
R2
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.
Adding the error term,
R1
VOUT = VREF 1 + ------ + IFBR2
R2
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
0.01µF
1µF
10kΩ
Supertex
VP12C
8
Output
5V±1%@
0 to 1A
IN
2
1
6
7
VTAP
SENSE
+
220µF
RC2951
FB
OUT
GND
4
2kΩ
1MΩ
0.002µF
IQഡ400µA
Figure 3. 1A Regulator with 1.2V Dropout
Unregulated
Input
+VIN
330Ω
8
6
1
2N5432
(2)
IN
OUT
8
+VIN
27kΩ
*VOUT≈VIN
1
5
3
RC2951
Error
Output
VOUT
ERROR
2
5V
Output
RC2951
SENSE
GND
VTAP
**Shutdown
Input
Load
+
FB
SD
GND
4.7µF
50mA to
300mA
4
7
FB
4
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
Figure 5. Wide Input Voltage Range
Current Limiter
1.23
R
Load
IL
IL=
8
VIN
1
VOUT
RC2951
Shutdown
Input
3
0.1µF
SD
GND
FB
4
7
+
R
1%
1 µF
Figure 6. Low Drift Current Source
REV. 1.0.0 2/8/01
7
RC2951
PRODUCT SPECIFICATION
Typical Applications (continued)
Current
Limit Section
+VIN
D1
+VIN = VOUT +5.0V
8
2
680
0.05
5V Memory
Supply
+VIN
D2
SENSE
VOUT
1
6
7
VTAP
FB
470
8
20
RC2951
#1
ERROR
MJE2955
+
5
1µF
2N3906
+VOUT @ 2A
10kΩ
3.6V
Nicad
GND
4
4.7MΩ
+VIN
5
Error
Flag
ERROR
R1
+
+
RC2951
7
27kΩ
4.7
TANT.
100
µF
3
1%
R2
SD
FB
EARLY WARNING
D3
VOUT
2.7MΩ
GND
4
220
D4
1
20kΩ
.033
47
Q1
RESET
8
2
330kΩ
µP
+VIN
SENSE
VOUT
Main 5V Output
R1
1
6
7
3
VOUT = 1.23V 1 +
(
)
VDD
VTAP
R2
For 5VOUT,use internal resistors. Wire pin 6 to 7, & wire pin 2 +VOUT Buss.
RC2951
FB
SD
+
#2
Figure 9. 2 Ampere Low Dropout Regulator
5
1µF
ERROR
GND
4
+VIN
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.
+VIN
+VOUT
5
3
1
Error
Output
ERROR
VOUT
100
pF
200kΩ
+
RC2951
3.3µF
Shutdown
Input
1%
SD
GND
2N3906
Figure 7. Regulator with Early Warning and Auxillary Output
FB
7
100kΩ
4
1%
100kΩ
+VIN
*High input lowers VOUT to 2.5V.
8
Figure 10. 5V Regulator with 2.5V Sleep Function
470kΩ
+VIN
VOUT
5
1
7
ERROR
RC2951
VOUT
470kΩ
+5V
R1
R2
+
4.7kΩ
3
4
20mA
1µF
SD
FB
Output*
5
Reset
8
GND
4
1
2
VIN
1
VOUT
1N
4001
RC2951
Figure 8. Latch Off When Error Flag Occurs
4
7
FB
0.1µF
GND
4
* High for
IL < 3.5mA
360
1N457
2950-13
Min. Voltages ≈ 4V
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
2
39kΩ
+VIN SENSE
+VOUT = 5V
RESET
1
5
3
ERROR
RC2951
VOUT
+
1µF
–
*C4
+
7
SD
GND
FB
VTAP
4
6
39kΩ
+
6V
Lead-Acid
Battery
100
kΩ
–
C1
+
100kΩ
100kΩ
1%
1%
< 5.8V**
< 6.0V**
1kΩ
1kΩ
–
C2
+
C1-C4
LP339
1%
–
100kΩ
C3
+
< 6.2V**
10kΩ
20kΩ
R3
1%
*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
+
120kΩ
1.5kΩ**
Lead-Acid
Battery
Source
8
+
1N457
+VIN
FB
LM385
1
Main V+
VOUT
RC2951
SENSE
–
2
7
Memory V+
≈ 400kΩ*
for 5.5V
3
SD
100kΩ
FB
VTAP
20Ω
GND
4
+
6
+
1µF
Ni-cad
Backup
Battery
*Sets disconnect Voltage
**Sets disconnect Hysteresis
Figure 13. Low Battery Disconnect
REV. 1.0.0 2/8/01
9
RC2951
PRODUCT SPECIFICATION
Mechanical Dimensions – 8 Lead SOIC
Notes:
Inches
Millimeters
Symbol
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
Min.
Max.
Min.
Max.
2. "D" and "E" do not include mold flash. Mold flash or
protrusions shall not exceed .010 inch (0.25mm).
A
.053
.004
.013
.008
.189
.150
.069
.010
.020
.010
.197
.158
1.35
0.10
0.33
0.20
4.80
3.81
1.75
0.25
0.51
0.25
5.00
4.01
A1
B
3. "L" is the length of terminal for soldering to a substrate.
4. Terminal numbers are shown for reference only.
5. "C" dimension does not include solder finish thickness.
6. Symbol "N" is the maximum number of terminals.
C
D
E
5
2
2
e
.050 BSC
1.27 BSC
H
h
.228
.010
.016
.244
.020
.050
5.79
0.25
0.40
6.20
0.50
1.27
L
3
6
N
α
8
8
0°
8°
0°
8°
ccc
—
.004
—
0.10
8
5
E
H
1
4
h x 45°
D
C
A1
A
α
SEATING
PLANE
– C –
L
e
LEAD COPLANARITY
ccc C
B
10
REV. 1.0.0 2/8/01
RC2951
PRODUCT SPECIFICATION
Ordering Information
Product Number
RC2951M
Package
8 pin SOIC
8 pin SOIC
RC2951M-3.3
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.
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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
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