NSC LP2951CSD Series of adjustable micropower voltage regulator Datasheet

LP2950/LP2951
Series of Adjustable Micropower Voltage Regulators
General Description
The LP2950 and LP2951 are micropower voltage regulators
with very low quiescent current (75µA typ.) and very low
dropout voltage (typ. 40mV at light loads and 380mV at
100mA). They are ideally suited for use in battery-powered
systems. Furthermore, the quiescent current of the LP2950/
LP2951 increases only slightly in dropout, prolonging battery
life.
The LP2950-5.0 is available in the surface-mount D-Pak
package, and in the popular 3-pin TO-92 package for pincompatibility with older 5V regulators. The 8-lead LP2951 is
available in plastic, ceramic dual-in-line, LLP, or metal can
packages and offers additional system functions.
One such feature is an error flag output which warns of a low
output voltage, often due to falling batteries on the input. It
may be used for a power-on reset. A second feature is the
logic-compatible shutdown input which enables the regulator
to be switched on and off. Also, the part may be pin-strapped
for a 5V, 3V, or 3.3V output (depending on the version), or
programmed from 1.24V to 29V with an external pair of
resistors.
Careful design of the LP2950/LP2951 has minimized all
contributions to the error budget. This includes a tight initial
tolerance (.5% typ.), extremely good load and line regulation
(.05% typ.) and a very low output voltage temperature coefficient, making the part useful as a low-power voltage reference.
Features
n
n
n
n
n
n
n
n
n
n
n
5V, 3V, and 3.3V versions available
High accuracy output voltage
Guaranteed 100mA output current
Extremely low quiescent current
Low dropout voltage
Extremely tight load and line regulation
Very low temperature coefficient
Use as Regulator or Reference
Needs minimum capacitance for stability
Current and Thermal Limiting
Stable with low-ESR output capacitors (10mΩ to 6Ω)
LP2951 versions only
n Error flag warns of output dropout
n Logic-controlled electronic shutdown
n Output programmable from 1.24 to 29V
Block Diagram and Typical Applications
LP2950
LP2951
00854625
00854601
© 2005 National Semiconductor Corporation
DS008546
www.national.com
LP2950/LP2951 Series of Adjustable Micropower Voltage Regulators
May 2005
LP2950/LP2951
Connection Diagrams
TO-252 (D-Pak)
TO-92 Plastic Package (Z)
00854602
Bottom View
00854670
Front View
Dual-In-Line Packages (N, J)
Surface-Mount Package (M, MM)
8-Lead LLP
00854626
Top View
Metal Can Package (H)
00854671
Pin 4 is fused to center DAP
Top View
00854619
Top View
10-Lead Ceramic Surface-Mount Package (WG)
00854664
Top View
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2
Package
Temperature
Range
Part Number
Package Marking
Transport Media
NSC Drawing
TO-92 (Z)
−40 < TJ < 125
LP2950ACZ-3.0
2950A CZ3.0
Bag
Z03A
LP2950CZ-3.0
2950 CZ3.0
Bag
LP2950ACZ-3.3
2950A CZ3.3
Bag
LP2950CZ-3.3
2950 CZ3.3
Bag
LP2950ACZ-5.0
2950A CZ5.0
Bag
LP2950CZ-5.0
2950 CZ5.0
Bag
LP2950CDT-3.0
LP2950CDT-3.0
75 Units/Rail
TO-252
(D-Pak)
−40 < TJ < 125
LP2950CDTX-3.0
LP2950CDT-3.3
2.5k Units Tape and Reel
LP2950CDT-3.3
LP2950CDTX-3.3
LP2950CDT-5.0
M (M08A)
−40 < TJ < 125
−40 < TJ < 125
LP2950CDT-5.0
2.5k Units Tape and Reel
LP2951ACN-3.0
40 Units/Rail
LP2951CN-3.0
LP2951CN-3.0
40 Units/Rail
LP2951ACN-3.3
LP2951ACN-3.3
40 Units/Rail
LP2951CN-3.3
LP2951CN-3.3
40 Units/Rail
LP2951ACN
LP2951ACN
40 Units/Rail
LP2951CN
LP2951CN
40 Units/Rail
LP2951ACM-3.0
2951ACM30*
(where * is die rev letter)
2.5k Units Tape and Reel
LP2951CM-3.0
95 Units/Rail
2951CM30*
(where * is die rev letter)
2.5k Units Tape and Reel
2951ACM33*
(where * is die rev letter)
2.5k Units Tape and Reel
2951CM33*
(where * is die rev letter)
2.5k Units Tape and Reel
2951ACM*
(where * is die rev letter)
2.5k Units Tape and Reel
LP2951CMX
2951CM*
(where * is die rev letter)
2.5k Units Tape and Reel
LP2951ACMM-3.0
L0BA
1k Units Tape and Reel
LP2951CMX-3.0
LP2951ACM-3.3
LP2951ACMX-3.3
LP2951CM-3.3
LP2951CMX-3.3
LP2951ACM
LP2951ACMX
LP2951CM
−40 < TJ < 125
75 Units/Rail
LP2951ACN-3.0
LP2951ACMX-3.0
MM
(MUA08A)
75 Units/Rail
2.5k Units Tape and Reel
LP2950CDTX-5.0
N (N-08E)
TD03B
LP2951ACMMX-3.0
N08E
M08A
95 Units/Rail
95 Units/Rail
95 Units/Rail
95 Units/Rail
95 Units/Rail
MUA08A
3.5k Units Tape and Reel
LP2951CMM-3.0
L0BB
LP2951CMMX-3.0
1k Units Tape and Reel
3.5k Units Tape and Reel
LP2951ACMM-3.3
L0CA
LP2951ACMMX-3.3
1k Units Tape and Reel
3.5k Units Tape and Reel
LP2951CMM-3.3
L0CB
LP2951CMMX-3.3
1k Units Tape and Reel
3.5k Units Tape and Reel
LP2951ACMM
L0DA
LP2951ACMMX
1k Units Tape and Reel
3.5k Units Tape and Reel
LP2951CMM
L0DB
LP2951CMMX
1k Units Tape and Reel
3.5k Units Tape and Reel
J (J08A)
−55 < TJ < 150
LP2951J/883
See MIL/AERO Datasheet
40 Units/Rail
J08A
H (H08C)
−55 < TJ < 150
LP2951H/883
See MIL/AERO Datasheet
Tray
H08C
WG
(WG10A)
−55 < TJ < 150
LP2951WG/883
See MIL/AERO Datasheet
Tray
WG10A
3
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LP2950/LP2951
Ordering Information
LP2950/LP2951
Ordering Information
Package
8-lead
LLP
Temperature
Range
−40 < TJ < 125
(Continued)
Part Number
Package Marking
LP2951ACSD-3.0
51AC30
LP2951ACSDX-3.0
LP2951CSD-3.0
51AC30B
51AC33B
2951AC
1k Units Tape and Reel
1k Units Tape and Reel
1k Units Tape and Reel
4.5k Units Tape and Reel
2951ACB
LP2951CSDX
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1k Units Tape and Reel
4.5k Units Tape and Reel
LP2951ACSDX
LP2951CSD
SDC08A
4.5k Units Tape and Reel
LP2951CSDX-3.3
LP2951ACSD
1k Units Tape and Reel
4.5k Units Tape and Reel
51AC33
LP2951ACSDX-3.3
LP2951CSD-3.3
NSC Drawing
4.5k Units Tape and Reel
LP2951CSDX-3.0
LP2951ACSD-3.3
Transport Media
1k Units Tape and Reel
4.5k Units Tape and Reel
4
ESD Rating
Human Body Model(Note 18)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Supply Voltage
Operating Ratings (Note 1)
−0.3 to +30V
Maximum Input Supply Voltage
SHUTDOWN Input Voltage,
Error Comparator Output
Voltage, (Note 9)
30V
Junction Temperature Range
(TJ) (Note 8)
FEEDBACK Input Voltage
−1.5 to +30V
(Note 9) (Note 10)
Power Dissipation
Internally Limited
Junction Temperature (TJ)
LP2951
−55˚ to +150˚C
LP2950AC-XX, LP2950C-XX,
LP2951AC-XX, LP2951C-XX
−40˚ to +125˚C
+150˚C
Ambient Storage Temperature
Soldering Dwell Time, Temperature
Wave
Infrared
Vapor Phase
2500V
−65˚ to +150˚C
4 seconds, 260˚C
10 seconds, 240˚C
75 seconds, 219˚C
Electrical Characteristics (Note 2)
LP2951
Conditions
(Note 2)
Parameter
Tested
Typ
Limit
Typ
(Notes 3, 16)
LP2950AC-XX
LP2950C-XX
LP2951AC-XX
LP2951C-XX
Tested
Design
Limit
Limit
Typ
(Note 3) (Note 4)
Tested
Design
Limit
Limit
Units
(Note 3) (Note 4)
3V Versions (Note 17)
Output Voltage
TJ = 25˚C
3.0
3.015
3.0
2.985
−25˚C ≤ TJ ≤ 85˚C
3.015
3.0
2.985
3.0
3.0
3.030
3.030
3.0
2.970
Full Operating
3.0
Temperature
Range
Output Voltage
100µA ≤ IL ≤
100mA
3.036
3.0
3.036
2.964
3.0
TJ ≤ TJMAX
3.0
2.964
3.045
3.042
3.0
2.955
V max
2.970
3.0
2.958
V min
3.045
V max
2.955
V min
3.060
V max
2.940
V min
3.072
V max
2.928
V min
3.3V Versions (Note 17)
Output Voltage
TJ = 25˚C
3.3
3.317
3.3
3.284
−25˚C ≤ TJ ≤ 85˚C
3.317
3.3
3.284
3.3
3.3
3.333
3.333
V max
3.267
V min
3.3
3.350
3.267
Full Operating
3.3
Temperature
Range
Output Voltage
100µA ≤ IL ≤
100mA
3.340
3.3
3.340
3.260
3.3
TJ ≤ TJMAX
3.3
3.260
3.350
3.346
3.3
3.251
3.3
3.254
V max
3.251
V min
3.366
V max
3.234
V min
3.379
V max
3.221
V min
5V Versions (Note 17)
Output Voltage
TJ = 25˚C
5.0
5.025
5.0
4.975
−25˚C ≤ TJ ≤ 85˚C
5.0
Full Operating
5.0
5.025
5.0
4.975
5.0
5.05
5.0
4.95
5.06
5.0
5
5.05
V max
4.95
5.06
5.0
V min
5.075
V max
4.925
V min
5.1
V max
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LP2950/LP2951
Absolute Maximum Ratings (Note 1)
LP2950/LP2951
Electrical Characteristics (Note 2)
(Continued)
LP2951
Parameter
Conditions
(Note 2)
Tested
Typ
Limit
Typ
(Notes 3, 16)
Temperature
Range
Output Voltage
100µA ≤ IL ≤
100mA
LP2950AC-XX
LP2950C-XX
LP2951AC-XX
LP2951C-XX
Tested
Design
Limit
Limit
(Note 3) (Note 4)
4.94
5.0
TJ ≤ TJMAX
Typ
Tested
Design
Limit
Limit
(Note 3) (Note 4)
4.94
5.075
5.075
5.0
4.925
Units
5.0
4.925
4.9
V min
5.12
V max
4.88
V min
150
ppm/˚C
All Voltage Options
Output Voltage
Temperature
Coefficient
(Note 12)
Line Regulation
(Note 14)
20
120
20
(VONOM + 1)V ≤
Vin ≤ 30V (Note
15)
0.03
0.1
0.03
Load Regulation
(Note 14)
100µA ≤ IL ≤
100mA
0.04
Dropout Voltage
(Note 5)
IL = 100µA
0.1
0.04
0.1
150
50
450
600
380
75
120
75
Vin = (VONOM −
0.5)V
170
200
0.2
0.3
150
50
600
380
8
12
150
120
170
12
160
200
0.05
0.2
200
170
160
200
0.05
0.2
µA max
mA max
14
110
mV max
µA max
14
110
mV max
mV max
600
140
8
% max
mV max
450
75
% max
% max
140
12
110
% max
80
120
14
Dropout
0.1
450
380
8
0.2
0.4
80
140
IL = 100mA
0.04
0.2
80
Current
50
0.2
0.3
50
IL = 100µA
0.1
0.5
IL = 100mA
Ground
100
mA max
µA max
Ground Current
IL = 100µA
Current Limit
Vout = 0
160
200
Thermal Regulation
(Note 13)
0.05
Output Noise,
CL = 1µF (5V
Only)
430
430
430
µV rms
10 Hz to 100 kHz
CL = 200µF
160
160
160
µV rms
100
100
100
µV rms
220
200
220
0.2
µA max
mA max
220
mA max
%/W
max
CL = 3.3µF
(Bypass = 0.01µF
Pins 7 to 1
(LP2951)
8-pin Versions Only
LP2951
Reference
1.235
Voltage
LP2951AC-XX
1.25
1.235
1.26
(Note 7)
Voltage
Feedback Pin
20
Bias Current
Reference Voltage
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1.22
1.26
V max
1.27
V max
1.21
V min
1.2
1.2
1.2
V min
1.27
1.27
1.285
V max
1.19
1.19
1.185
40
20
60
(Note 12)
LP2951C-XX
1.235
1.26
1.22
Reference
1.25
40
20
60
20
20
6
40
60
50
V min
nA max
nA max
ppm/˚C
(Continued)
LP2951
Parameter
Conditions
(Note 2)
Tested
Typ
Limit
Typ
(Notes 3, 16)
LP2950AC-XX
LP2950C-XX
LP2951AC-XX
LP2951C-XX
Tested
Design
Limit
Limit
Typ
(Note 3) (Note 4)
Tested
Design
Limit
Limit
Units
(Note 3) (Note 4)
All Voltage Options
Temperature
Coefficient
Feedback Pin Bias
0.1
0.1
0.1
nA/˚C
Current Temperature
Coefficient
Error Comparator
Output Leakage
VOH = 30V
0.01
1
Output Low
Vin = (VONOM −
0.5)V
150
250
Voltage
IOL = 400µA
Upper Threshold
(Note 6)
Current
150
250
60
75
40
60
40
150
250
95
75
µA max
mV max
400
60
95
µA max
2
40
25
140
(Note 6)
1
400
25
(Note 6)
0.01
2
400
Voltage
Hysteresis
1
2
Voltage
Lower Threshold
0.01
mV min
25
75
mV min
95
140
mV max
mV max
140
mV max
15
15
15
mV
1.3
1.3
1.3
V
Shutdown Input
Input
Logic
Low (Regulator
ON)
0.6
0.7
0.7
V max
Voltage
High (Regulator
OFF)
2.0
2.0
2.0
V min
Shutdown Pin Input
Current
Vshutdown = 2.4V
100
µA max
30
50
30
50
100
Vshutdown = 30V
450
600
450
600
750
Regulator Output
Current in Shutdown
(Note 11)
3
30
50
100
450
600
750
10
3
20
10
µA max
750
3
20
µA max
10
µA max
µA max
20
µA max
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device
is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical
Characteristics tables.
Note 2: Unless otherwise specified all limits guaranteed for VIN = (VONOM + 1)V, IL = 100µA and CL = 1µF for 5V versions and 2.2µF for 3V and 3.3V versions. Limits
appearing in boldface type apply over the entire junction temperature range for operation. Limits appearing in normal type apply for TA = TJ = 25˚C. Additional
conditions for the 8-pin versions are FEEDBACK tied to VTAP, OUTPUT tied to SENSE, and VSHUTDOWN ≤ 0.8V.
Note 3: Guaranteed and 100% production tested.
Note 4: Guaranteed but not 100% production tested. These limits are not used to calculate outgoing AQL levels.
Note 5: 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.
Note 6: 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 95mV 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.
Note 7: Vref ≤ Vout ≤ (Vin − 1V), 2.3V ≤ Vin ≤ 30V, 100µA ≤ IL ≤ 100mA, TJ ≤ TJMAX.
Note 8: The junction-to-ambient thermal resistances are as follows: 180˚C/W and 160˚C/W for the TO-92 package with 0.40 inch and 0.25 inch leads to the printed
circuit board (PCB) respectively, 105˚C/W for the molded plastic DIP (N), 130˚C/W for the ceramic DIP (J), 160˚C/W for the molded plastic SOP (M), 200˚C/W for
the molded plastic MSOP (MM), and 160˚C/W for the metal can package (H). The above thermal resistances for the N, J, M, and MM packages apply when the
package is soldered directly to the PCB. Junction-to-case thermal resistance for the H package is 20˚C/W. Junction-to-case thermal resistance for the TO-252
package is 5.4˚C/W. The value of θJA for the LLP package is typically 51˚C/W but is dependent on the PCB trace area, trace material, and the number of layers and
thermal vias. For details of thermal resistance and power dissipation for the LLP package, refer to Application Note AN-1187.
Note 9: May exceed input supply voltage.
7
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LP2950/LP2951
Electrical Characteristics (Note 2)
LP2950/LP2951
Electrical Characteristics (Note 2)
(Continued)
Note 10: 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.
Note 11: Vshutdown ≥ 2V, Vin ≤ 30V, Vout = 0, Feedback pin tied to VTAP.
Note 12: Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
Note 13: 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 50mA load pulse at VIN = 30V (1.25W pulse) for T = 10ms.
Note 14: 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.
Note 15: Line regulation for the LP2951 is tested at 150˚C for IL = 1mA. For IL = 100µA 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.
Note 16: A Military RETS specification is available on request. At time of printing, the LP2951 RETS specification complied with the boldface limits in this column.
The LP2951H, WG, or J may also be procured as Standard Military Drawing Spec #5962-3870501MGA, MXA, or MPA.
Note 17: All LP2950 devices have the nominal output voltage coded as the last two digits of the part number. In the LP2951 products, the 3.0V and 3.3V versions
are designated by the last two digits, but the 5V version is denoted with no code at this location of the part number (refer to ordering information table).
Note 18: Human Body Model 1.5kΩ in series with 100pF.
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8
LP2950/LP2951
Typical Performance Characteristics
Quiescent Current
Dropout Characteristics
00854628
00854627
Input Current
Input Current
00854629
00854630
Output Voltage vs. Temperature of 3
Representative Units
Quiescent Current
00854632
00854631
9
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LP2950/LP2951
Typical Performance Characteristics
(Continued)
Quiescent Current
Quiescent Current
00854633
00854634
Quiescent Current
Short Circuit Current
00854635
00854636
Dropout Voltage
Dropout Voltage
00854638
00854637
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10
LP2950/LP2951
Typical Performance Characteristics
(Continued)
LP2951 Minimum Operating Voltage
LP2951 Feedback Bias Current
00854639
00854640
LP2951 Feedback Pin Current
LP2951 Error Comparator Output
00854642
00854641
LP2951 Comparator Sink Current
Line Transient Response
00854643
00854644
11
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LP2950/LP2951
Typical Performance Characteristics
(Continued)
Load Transient Response
Load Transient Response
00854645
00854646
LP2951 Enable Transient
Output Impedance
00854648
00854647
Ripple Rejection
Ripple Rejection
00854649
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00854650
12
LP2950/LP2951
Typical Performance Characteristics
(Continued)
Ripple Rejection
LP2951 Output Noise
00854651
00854652
LP2951 Divider Resistance
Shutdown Threshold Voltage
00854653
00854654
Line Regulation
LP2951 Maximum Rated Output Current
00854656
00854655
13
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LP2950/LP2951
Typical Performance Characteristics
(Continued)
LP2950 Maximum Rated Output Current
Thermal Response
00854657
00854658
Output Capacitor ESR Range
00854663
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14
EXTERNAL CAPACITORS
A 1.0µF (or greater) capacitor is required between the output
and ground for stability at output voltages of 5V or more. At
lower output voltages, more capacitance is required (2.2µF
or more is recommended for 3V and 3.3V versions). Without
this capacitor the part will oscillate. Most types of tantalum or
aluminum electrolytics work fine here; even film types work
but are not recommended for reasons of cost. Many aluminum electrolytics have electrolytes that freeze at about
−30˚C, so solid tantalums are recommended for operation
below −25˚C. The important parameters of the capacitor are
an ESR of about 5Ω or less and a resonant frequency above
500kHz. The value of this capacitor may be increased without limit.
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 400µA, this
sink current adds to battery drain in a low battery condition.
Suggested values range from 100k to 1 MΩ. The resistor is
not required if this output is unused.
Ceramic capacitors whose value is greater than 1000pF
should not be connected directly from the LP2951 output to
ground. Ceramic capacitors typically have ESR values in the
range of 5 to 10mΩ, a value below the lower limit for stable
operation (see curve Output Capacitor ESR Range).
The reason for the lower ESR limit is that the loop compensation of the part relies on the ESR of the output capacitor to
provide the zero that gives added phase lead. The ESR of
ceramic capacitors is so low that this phase lead does not
occur, significantly reducing phase margin. A ceramic output
capacitor can be used if a series resistance is added (recommended value of resistance about 0.1Ω to 2Ω).
At lower values of output current, less output capacitance is
required for stability. The capacitor can be reduced to 0.33µF
for currents below 10mA or 0.1µF for currents below 1mA.
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 100mA
load at 1.23V output (Output shorted to Feedback) a 3.3µF
(or greater) capacitor should be used.
Unlike many other regulators, the LP2950 will remain stable
and in regulation with no load in addition to the internal
voltage divider. This is especially important in CMOS RAM
keep-alive applications. When setting the output voltage of
the LP2951 versions with external resistors, a minimum load
of 1µA is recommended.
00854620
*When VIN ≤ 1.3V, the error flag pin becomes a high impedance, and the
error flag voltage rises to its pull-up voltage. Using VOUT as the pull-up
voltage (see Figure 2), rather than an external 5V source, will keep the
error flag voltage under 1.2V (typ.) in this condition. The user may wish to
divide down the error flag voltage using equal-value resistors (10kΩ
suggested), to ensure a low-level logic signal during any fault condition,
while still allowing a valid high logic level during normal operation.
FIGURE 1. ERROR Output Timing
PROGRAMMING THE OUTPUT VOLTAGE (LP2951)
The LP2951 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.
The complete equation for the output voltage is
A 1µF tantalum, ceramic or aluminum electrolytic capacitor
should be placed from the LP2950/LP2951 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 LP2951 Feedback terminal can
cause instability. This may especially be a problem when
using high value external resistors to set the output voltage.
Adding a 100pF capacitor between Output and Feedback
and increasing the output capacitor to at least 3.3µF will fix
this problem.
ERROR DETECTION COMPARATOR OUTPUT
The comparator produces a logic low output whenever the
LP2951 output falls out of regulation by more than approximately 5%. This figure is the comparator’s built-in offset of
about 60mV divided by the 1.235 reference voltage. (Refer
to the block diagram in the front of the datasheet.) This trip
level remains “5% below normal” regardless of the programmed output voltage of the 2951. 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.
where VREF is the nominal 1.235 reference voltage and IFB is
the feedback pin bias current, nominally −20nA. The minimum recommended load current of 1µA 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 12µA. Since the
LP2951 typically draws 60µA at no load with Pin 2 opencircuited, this is a small price to pay.
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LP2950/LP2951
Figure 1 below gives a timing diagram depicting the ERROR
signal and the regulated output voltage as the LP2951 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 = 4.75V).
Since the LP2951’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.
Application Hints
LP2950/LP2951
Application Hints
(Continued)
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. This is the only way noise can be reduced on the
3 lead LP2950 but is relatively inefficient, as increasing the
capacitor from 1µF to 220µF only decreases the noise from
430µV to 160µV rms for a 100kHz bandwidth at 5V output.
Noise can be reduced fourfold by a bypass capacitor across
R1, since it reduces the high frequency gain from 4 to unity.
Pick
or about 0.01µF. When doing this, the output capacitor must
be increased to 3.3µF to maintain stability. These changes
reduce the output noise from 430µV to 100µV rms for a
100kHz 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.
00854607
*See Application Hints
**Drive with TTL-high to shut down. Ground or leave open if shutdown
feature is not to be used.
Note: Pins 2 and 6 are left open.
FIGURE 2. Adjustable Regulator
Typical Applications
1A Regulator with 1.2V Dropout
00854622
300mA Regulator with 0.75V Dropout
Wide Input Voltage Range Current Limiter
00854621
00854609
*Minimum input-output voltage ranges from 40mV to 400mV, depending on
load current. Current limit is typically 160mA.
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16
LP2950/LP2951
Typical Applications
(Continued)
Low Drift Current Source
5 Volt Current Limiter
00854610
*Minimum input-output voltage ranges from 40mV to 400mV, depending on
load current. Current limit is typically 160mA.
00854608
Regulator with Early Warning and Auxiliary Output
Latch Off When Error Flag Occurs
00854612
00854611
j Early warning flag on low input voltage
j Main output latches off at lower input voltages
j Battery backup on auxiliary output
j Operation: Reg. #1’s Vout is programmed one diode drop above 5V. Its
error flag becomes active when Vin ≤ 5.7V. When Vin 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.
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LP2950/LP2951
Typical Applications
(Continued)
2 Ampere Low Dropout Regulator
00854613
For 5Vout, use internal resistors. Wire pin 6 to 7, & wire pin 2 to +Vout Bus.
Open Circuit Detector for 4 → 20mA Current Loop
5V Regulator with 2.5V Sleep Function
00854615
00854614
*High input lowers Vout to 2.5V
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18
LP2950/LP2951
Typical Applications
(Continued)
Regulator with State-of-Charge Indicator
00854616
*Optional Latch off when drop out occurs. Adjust R3 for C2 Switching when Vin is 6.0V.
**Outputs go low when Vin drops below designated thresholds.
Low Battery Disconnect
00854617
For values shown, Regulator shuts down when Vin < 5.5V and turns on again at 6.0V. Current drain in disconnected mode is ≈ 150µA.
*Sets disconnect Voltage
**Sets disconnect Hysteresis
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LP2950/LP2951
Typical Applications
(Continued)
System Overtemperature Protection Circuit
00854618
LM34 for 125˚F Shutdown
LM35 for 125˚C Shutdown
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Schematic Diagram
00854623
LP2950/LP2951
21
LP2950/LP2951
Physical Dimensions
inches (millimeters) unless otherwise noted
Order Number LP2951WG/883
NS Package Number WG10A
Metal Can Package (H)
NS Package Number H08C
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22
LP2950/LP2951
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Ceramic Dual-In-Line Package (J)
NS Package Number J08A
Surface Mount Package (M)
NS Package Number M08A
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LP2950/LP2951
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Molded Dual-In-Line Package (N)
NS Package Number N08E
Molded TO-92 Package (Z)
NS Package Number Z03A
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24
LP2950/LP2951
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Surface Mount Package (MM)
NS Package Number MUA08A
D-Pak Package
NS Package Number TD03B
25
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LP2950/LP2951 Series of Adjustable Micropower Voltage Regulators
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
LLP Package
NS Package Number SDC08A
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