LP2950/A-XX and LP2951/A-XX
Series of Adjustable Micropower Voltage Regulators
General Description
The LP2950 and LP2951 are micropower voltage regulators
with very low quiescent current (75 µA typ.) and very low
dropout voltage (typ. 40 mV at light loads and 380 mV at
100 mA). 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
The LP2950-5.0 in the popular 3-pin TO-92 package is
pin-compatible with older 5V regulators. The 8-lead LP2951
is available in plastic, ceramic dual-in-line, 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 re-
Careful design of the LP2950/LP2951 has minimized all con-
tributions to the error budget. This includes a tight initial tol-
erance (.5%typ.), extremely good load and line regulation
(.05%typ.) and a very low output voltage temperature coef-
ficient, making the part useful as a low-power voltage refer-
n5V, 3V, and 3.3V versions available
nHigh accuracy output voltage
nGuaranteed 100 mA output current
nExtremely low quiescent current
nLow dropout voltage
nExtremely tight load and line regulation
nVery low temperature coefficient
nUse as Regulator or Reference
nNeeds minimum capacitance for stability
nCurrent and Thermal Limiting
LP2951 versions only
nError flag warns of output dropout
nLogic-controlled electronic shutdown
nOutput programmable from 1.24 to 29V
Block Diagram and Typical Applications
June 1997
LP2950/A-XX and LP2951/A-XX Series of Adjustable Micropower Voltage Regulators
© 1997 National Semiconductor Corporation DS008546 www.national.com
Connection Diagrams
TO-92 Plastic Package (Z)
Bottom View
Dual-In-Line Packages (N, J)
Surface-Mount Package (M, MM)
Top View
Metal Can Package (H)
Top View
Leadless Chip Carrier (E)
Top View
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Ordering Information
Package Output Voltage Temperature
3.0V 3.3V 5.0V (˚C)
TO-92 (Z) LP2950ACZ-3.0 LP2950ACZ-3.3 LP2950ACZ-5.0 −40 <T
LP2950CA-3.0 LP2950CZ-3.3 LP2950CZ-5.0
N (N-08E) LP2951ACN-3.0 LP2951ACN-3.3 LP2951ACN −40 <T
LP2951CN-3.0 LP2951CN-3.3 LP2950CN
M (M08A) LP2951ACM-3.0 LP2951ACM-3.3 LP2951ACM −40 <T
LP2951CM-3.0 LP2951CM-3.3 LP2951CM
MM (MUA08A) LP2951ACMM-3.0 LP2951ACMM-3.3 LP2951ACMM −40 <T
LP2951CMM-3.0 LP2951CMM-3.3 LP2951CMM
J (J08A) LP2951ACJ −40 <T
LP2951J −55 <T
H (H08C) LP2951H/883 −55 <T
E (E20A) LP2951E/883 −55 <T
For MM Package:
Order Number Package Marking
LP2951ACMM-3.3 L0CA
LP2951CMM-3.3 L0CB
LP2951ACMM-3.0 L0BA
LP2951CMM-3.0 L0BB
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Supply Voltage −0.3 to +30V
SHUTDOWN Input Voltage,
Error Comparator Output
Voltage, (Note 9)
FEEDBACK Input Voltage −1.5 to +30V
(Note 9) (Note 10)
Power Dissipation Internally Limited
Junction Temperature (T
) +150˚C
Ambient Storage Temperature −65˚ to +150˚C
Soldering Dwell Time, Temperature
Wave 4 seconds, 260˚C
Infrared 10 seconds, 240˚C
Vapor Phase 75 seconds, 219˚C
Operating Ratings (Note 1)
Maximum Input Supply Voltage 30V
Junction Temperature Range
) (Note 8)
LP2951 −55˚ to +150˚C
LP2950AC-XX, LP2950C-XX,
LP2951AC-XX, LP2951C-XX −40˚ to +125˚C
Electrical Characteristics (Note 2)
Parameter Conditions
(Note 2)
LP2951 LP2950AC-XX LP2950C-XX
LP2951AC-XX LP2951C-XX
Tested Tested Design Tested Design
Typ Limit Typ Limit Limit Typ Limit Limit
(Notes 3, 16) (Note 3) (Note 4) (Note 3) (Note 4)
3V VERSIONS (Note 17)
Output Voltage TJ=25˚C 3.0 3.015 3.0 3.015 3.0 3.030 V max
2.985 2.985 2.970 V min
−25˚C TJ85˚C 3.0 3.0 3.030 3.0 3.045 V max
2.970 2.955 V min
Full Operating 3.0 3.036 3.0 3.036 3.0 3.060 V max
Temperature Range 2.964 2.964 2.940 V min
Output Voltage 100 µA IL100 mA 3.0 3.045 3.0 3.042 3.0 3.072 V max
TJTJMAX 2.955 2.958 2.928 V min
3.3V VERSIONS (Note 17)
Output Voltage TJ=25˚C 3.3 3.317 3.3 3.317 3.3 3.333 V max
3.284 3.284 3.267 V min
−25˚C TJ85˚C 3.3 3.3 3.333 3.3 3.350 V max
3.267 3.251 V min
Full Operating 3.3 3.340 3.3 3.340 3.3 3.366 V max
Temperature Range 3.260 3.260 3.234 V min
Output Voltage 100 µA IL100 mA 3.3 3.350 3.3 3.346 3.3 3.379 V max
TJTJMAX 3.251 3.254 3.221 V min
5V VERSIONS (Note 17)
Output Voltage TJ=25˚C 5.0 5.025 5.0 5.025 5.0 5.05 V max
4.975 4.975 4.95 V min
−25˚C TJ85˚C 5.0 5.0 5.05 5.0 5.075 V max
4.95 4.925 V min
Full Operating 5.0 5.06 5.0 5.06 5.0 5.1 V max
Temperature Range 4.94 4.94 4.9 V min
Output Voltage 100 µA IL100 mA 5.0 5.075 5.0 5.075 5.0 5.12 V max
TJTJMAX 4.925 4.925 4.88 V min
Output Voltage
Temperature Coefficient (Note 12) 20 120 20 100 50 150 ppm/˚C
Line Regulation
(Note 14) (VONOM + 1)V Vin 30V
(Note 15) 0.03 0.1 0.03 0.1 0.04 0.2 %max
0.5 0.2 0.4 %max
Load Regulation
(Note 14) 100 µA IL100 mA 0.04 0.1 0.04 0.1 0.1 0.2 %max
0.3 0.2 0.3 %max
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Electrical Characteristics (Note 2) (Continued)
Parameter Conditions
(Note 2)
LP2951 LP2950AC-XX LP2950C-XX
LP2951AC-XX LP2951C-XX
Tested Tested Design Tested Design
Typ Limit Typ Limit Limit Typ Limit Limit
(Notes 3, 16) (Note 3) (Note 4) (Note 3) (Note 4)
Dropout Voltage
(Note 5) IL=100 µA 80 80 80 mV max
50 150 50 150 50 150 mV max
IL=100 mA 450 450 450 mV max
380 600 380 600 380 600 mV max
Ground IL=100 µA 75 120 75 120 75 120 µA max
Current 140 140 140 µA max
IL=100 mA 8 12 8 12 8 12 mA max
14 14 14 mA max
Dropout Vin =(VONOM 0.5)V 110 170 110 170 110 170 µA max
Ground Current IL=100 µA 200 200 200 µA max
Current Limit Vout =0 160 200 160 200 160 200 mA max
220 220 220 mA max
Thermal Regulation (Note 13) 0.05 0.2 0.05 0.2 0.05 0.2 %/W max
Output Noise, CL=1 µF (5V Only) 430 430 430 µV rms
10 Hz to 100 KHz CL=200 µF 160 160 160 µV rms
CL=3.3 µF
(Bypass =0.01 µF 100 100 100 µV rms
Pins 7 to 1 (LP2951))
Reference 1.235 1.25 1.235 1.25 1.235 1.26 V max
Voltage 1.26 1.26 1.27 V max
1.22 1.22 1.21 V min
1.2 1.2 1.2 V min
Reference (Note 7) 1.27 1.27 1.285 V max
Voltage 1.19 1.19 1.185 V min
Feedback Pin 20 40 20 40 20 40 nA max
Bias Current 60 60 60 nA max
Reference Voltage (Note 12) 20 20 50 ppm/˚C
Temperature Coefficient
Feedback Pin Bias 0.1 0.1 0.1 nA/˚C
Current Temperature
Error Comparator
Output Leakage VOH =30V 0.01 1 0.01 1 0.01 1 µA max
Current 222µA max
Output Low Vin =(VONOM 0.5)V 150 250 150 250 150 250 mV max
Voltage IOL =400 µA 400 400 400 mV max
Upper Threshold (Note 6) 60 40 60 40 60 40 mV min
Voltage 25 25 25 mV min
Lower Threshold (Note 6) 75 95 75 95 75 95 mV max
Voltage 140 140 140 mV max
Hysteresis (Note 6) 15 15 15 mV
Shutdown Input
Input 1.3 1.3 1.3 V
Logic Low (Regulator ON) 0.6 0.7 0.7 V max
Voltage High (Regulator OFF) 2.0 2.0 2.0 V min
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Electrical Characteristics (Note 2) (Continued)
Parameter Conditions
(Note 2)
LP2951 LP2950AC-XX LP2950C-XX
LP2951AC-XX LP2951C-XX
Tested Tested Design Tested Design
Typ Limit Typ Limit Limit Typ Limit Limit
(Notes 3, 16) (Note 3) (Note 4) (Note 3) (Note 4)
Shutdown Input
Shutdown Pin Input
Current Vshutdown =2.4V 30 50 30 50 30 50 µA max
100 100 100 µA max
Vshutdown =30V 450 600 450 600 450 600 µA max
750 750 750 µA max
Regulator Output
Current in Shutdown (Note 11) 3 10 3 10 3 10 µA max
20 20 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=100 µA and CL=1 µF for 5V versions and 2.2 µF 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=T
J= 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 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.
Note 7: Vref Vout (Vin 1V), 2.3V Vin 30V, 100 µA IL100 mA, TJTJMAX.
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), 160˚C/W for the metal can package (H), and 180˚C/W for the leadless chip carrier (E). The above thermal resistances for the N, J, M,
MM, and E packages apply when the package is soldered directly to the PCB. Junction-to-case thermal resistances for the E and H packages are 24˚C/W and 20˚C/W
Note 9: May exceed input supply voltage.
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
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 50 mA load pulse at VIN =30V (1.25W pulse) for T =10 ms.
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=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.
Note 16: A Military RETS spec is available on request. At time of printing, the LP2951 RETS spec complied with the boldface limits in this column. The LP2951H,
E, or J may also be procured as Standard Military Drawing Spec #5962-3870501MGA, M2A, 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).
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Typical Performance Characteristics
Quiescent Current
Dropout Characteristics
Input Current
Input Current
Output Voltage vs.
Temperature of 3
Representative Units
Quiescent Current
Quiescent Current
Quiescent Current
Quiescent Current
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Typical Performance Characteristics (Continued)
Short Circuit Current
Dropout Voltage
Dropout Voltage
Minimum Operating Voltage
Feedback Bias Current
Feedback Pin Current
Error Comparator Output
Comparator Sink Current
Line Transient Response
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Typical Performance Characteristics (Continued)
Load Transient Response
Load Transient Response
Enable Transient
Output Impedance
Ripple Rejection
Ripple Rejection
Ripple Rejection
LP2951 Output Noise
LP2951 Divider Resistance
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Typical Performance Characteristics (Continued)
Application Hints
A 1.0 µF (or greater) capacitor is required between the out-
put and ground for stability at output voltages of 5V or more.
At lower output voltages, more capacitance is required
(2.2 µF 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 op-
eration below −25˚C. The important parameters of the ca-
pacitor are an ESR of about 5 or less and a resonant fre-
quency above 500 kHz. The value of this capacitor may be
increased without limit.
At lower values of output current, less output capacitance is
required for stability. The capacitor can be reduced to
0.33 µF for currents below 10 mA or 0.1 µF for currents be-
low 1 mA. Using the adjustable versions at voltages below
5V runs the error amplifier at lower gains so that
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.
Unlike many other regulators, the LP2950 will remain stable
and in regulation with no load in addition to the internal volt-
age 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 1 µA is recommended.
A1 µF tantalum 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 theAC fil-
ter 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 us-
ing 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.
The comparator produces a logic low output whenever the
LP2951 output falls out of regulation by more than approxi-
mately 5%. This figure is the comparator’s built-in offset of
about 60 mV 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 pro-
grammed 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 ei-
ther to low input voltage, current limiting, or thermal limiting.
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 V
Since the LP2951’s dropout voltage is load-dependent (see
Shutdown Threshold Voltage
Line Regulation
LP2951 Maximum
Rated Output Current
LP2950 Maximum
Rated Output Current
Thermal Response
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Application Hints (Continued)
curve in typical performance characteristics), the input volt-
age trip point (about 5V) will vary with the load current. The
output voltage trip point (approx. 4.75V) does not vary with
The error comparator has an open-collector output which re-
quires an external pullup resistor. This resistor may be re-
turned to the output or some other supply voltage depending
on system requirements. In determining a value for this re-
sistor, 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 1 M. The resistor is
not required if this output is unused.
The LP2951 may be pin-strapped for the nominal fixed out-
put voltage using its internal voltage divider by tying the out-
put and sense pins together, and also tying the feedback and
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 re-
sistors is required.
The complete equation for the output voltage is
where V
is the nominal 1.235 reference voltage and I
the feedback pin bias current, nominally −20 nA. The mini-
mum recommended load current of 1 µA forces an upper
limit of 1.2 Mon the value of R
, if the regulator must work
with no load (a condition often found in CMOS in standby).
will produce a 2%typical error in V
which may be
eliminated at room temperature by trimming R
. For better
accuracy, choosing R
=100k reduces this error to 0.17%
while increasing the resistor program current to 12 µA. Since
the LP2951 typically draws 60 µA at no load with Pin 2
open-circuited, this is a small price to pay.
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 1 µF to 220 µF only decreases the noise from
430 µV to 160 µV rms for a 100 kHz bandwidth at 5V output.
Noise can be reduced fourfold by a bypass capacitor ac-
cross R
, since it reduces the high frequency gain from 4 to
unity. Pick
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 im-
provements are more dramatic at higher output voltages.
*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 (10 k
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
*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
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Typical Applications
1A Regulator with 1.2V Dropout
300 mA Regulator with 0.75V Dropout
Wide Input Voltage Range Current
*Minimum input-output voltage ranges from 40 mV to
400 mV, depending on load current. Current limit is
typically 160 mA.
Low Drift Current Source
5 Volt Current Limiter
*Minimum input-output voltage ranges from 40 mV to
400 mV, depending on load current. Current limit is
typically 160 mA.
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Typical Applications (Continued)
Regulator with Early Warning and Auxiliary Output
jEarly warning flag on low input voltage
jMain output latches off at lower input voltages
jBattery backup on auxiliary output
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.
Latch Off When Error Flag Occurs
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Typical Applications (Continued)
2 Ampere Low Dropout Regulator
For 5Vout, use internal resistors. Wire pin 6 to 7, & wire pin 2 to +Vout Buss.
5V Regulator with 2.5V Sleep Function
*High input lowers Vout to 2.5V
Open Circuit Detector for 4 20 mA Current Loop
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Typical Applications (Continued)
Regulator with State-of-Charge Indicator
*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
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.
*Sets disconnect Voltage
**Sets disconnect Hysteresis
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Typical Applications (Continued)
System Overtemperature Protection Circuit
LM34 for 125˚F Shutdown
LM35 for 125˚C Shutdown
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Schematic Diagram
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Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LP2951E/883 or 5962-3870501M2A
NS Package Number E20A
Metal Can Package (H)
Order Number LP2951H/883 or 5962-3870501MGA
NS Package Number H08C
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Ceramic Dual-In-Line Package (J)
Order Number LP2951CJ, LP2951ACJ, LP2951J, LP2951J/883 or 5962-3870501MPA
NS Package Number J08A
Surface Mount Package (M)
Order Number LP2951ACM, LP2951CM, LP2951ACM-3.0,
LP2951CM-3.0, LP2951ACM-3.3 or LP2951CM-3.3
NS Package Number M08A
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Molded Dual-In-Line Package (N)
Order Number LP2951ACN, LP2951CN, LP2951ACN-3.0,
LP2951CN-3.0, or LP2951ACN-3.3 or LP2951CN-3.3
NS Package Number N08E
Molded TO-92 Package (Z)
Order Number LP2950ACZ-3.0 or LP2950CZ-3.0, LP2950ACZ-3.3,
LP2950CZ-3.3, LP2950ACZ-5.0 or LP2950CZ-5.0
NS Package Number Z03A
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