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Advanced
LP2950/LP2951
Monolithic
100mA LOW DROPOUT VOLTAGE REGULATOR
Systems
FEATURES
APPLICATIONS
5V, 3.3V, and 3V Versions at 100mA Output Current
Battery Powered Systems
High Accuracy Output Voltage
Portable Consumer Equipment
Extremely Low Quiescent Current
Cordless Telephones
Low Dropout Voltage
Portable (Notebook) Computers
Extremely Tight Load and Line Regulation
Portable Instrumentation
Very Low Temperature Coefficient
Radio Control Systems
Current and Thermal Limiting
Automotive Electronics
Needs Minimum Capacitance (1
F) for Stability
Avionics
Unregulated DC Positive Transients 60V
Low-Power Voltage Reference
ADDITIONAL FEATURES (LP2951 ONLY)
1.24V to 29V Programmable Output
Error Flag Warning of Voltage Output Dropout
Logic Controlled Electronic Shutdown
GENERAL DESCRIPTION
The LP2950 and LP2951 are micropower voltage regulators ideally suited for use in battery-powered systems. These devices
feature very low quiescent current (typ.75A), and very low dropout voltage (typ.45mV at light loads and 380mV at 100mA)
thus prolonging battery life. The quiescent current increases only slightly in dropout. The LP2950/LP2951 has positive
transient protection up to 60V and can survive unregulated input transient up to 20V below ground.
The LP2950 and LP2951 were designed to include a tight initial tolerance (typ. 0.5%), excellent load and line regulation (typ.
0.05%), and a very low output voltage temperature coefficient, making these devices useful as a low-power voltage reference.
The LP2950 is offered in the 3-pin TO-92 package. LP2951 is available in 8-pin plastic SOIC and DIP packages and offers
three major additional system features. An error flag output warns of a low output voltage, often due to failing batteries on
input. The LP2951 also features the logic-compatible shutdown input which enables the regulator to be switched on and off.
The LP2951 device may be pin-strapped for a 5V, 3.3V, or 3V output, or programmed from 1.24V to 29V with an external
pair of resistors.
ORDERING INFORMATION PIN CONNECTION
PACKAGE TYPE
OPERATING
TO-92
8 LEAD PDIP 8 LEAD SOIC
TEMP. RANGE
LP2950ACN-X LP2951ACP-X LP2951ACS-X
IND.
LP2950CN-X
LP2951CP-X
LP2951CS-X
IND
X = 3.3V, or 3V
8L SOIC/ 8L PDIP
1
2
8
4
3
7
5
6 V
TAP
ERROR
FEEDBACK
OUTPUT
SENSE
SHUTDOWN
INPUT
GROUND
Top View
TO-92
OUTPUT
INPUT
GND
Bottom View
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LP2950/LP2951
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage
-0.3 to +30V
Wave
4 seconds, 260
C
SHUTDOWN Input Voltage,
Infrared
4 seconds, 240
C
Error Comparator Output
Vapor Phase
4 seconds, 219
C
Voltage,(Note 9)
ESD
TBD
FEEDBACK Input Voltage
-1.5 to +30V
(Note 9) (Note 10)
OPERATING RATINGS
(Note 1)
Power Dissipation
Internally Limited
Junction Temperature
+150
C
Max. Input Supply Voltage 30V
Storage Temperature
-65
C to +150
C
Junction Temperature Range
Soldering Dwell Time, Temperature
(T
J
) (Note 8)
LP2950AC-XX, LP2950C-XX
LP2951AC-XX, LP2951C-XX
-40
C to +125
C
ELECTRICAL CHARACTERISTICS
at Vs=Vout+1V, Ta=25C, unless otherwise noted
.
Parameter
Conditions
(Note 2)
LP2950AC
LP2951AC
Min. Typ. Max.
LP2950C
LP2951C
Min. Typ. Max.
Units
3 V Versions (Note 16)
Output Voltage
TJ = 25C (Note 3)
-25C
TJ
85C
Full Operating Temperature Range
2.985
2.970
2.964
3.0
3.0
3.0
3.015
3.030
3.036
2.970
2.955
2.940
3.0
3.0
3.0
3.030
3.045
3.060
V
V
V
Output Voltage
100
A
IL
100 mA
TJ
TJMAX
2.958
3.0
3.042
2.928
3.0
3.072
V
3.3 V Versions (Note 16)
Output Voltage
TJ = 25C (Note 3)
-25C
TJ
85C
Full Operating Temperature Range
3.284
3.267
3.260
3.3
3.3
3.3
3.317
3.333
3.340
3.267
3.251
3.234
3.3
3.3
3.3
3.333
3.350
3.366
V
V
V
Output Voltage
100
A
IL
100 mA
TJ
TJMAX
3.254
3.3
3.346
3.221
3.3
3.379
V
5 V Versions (Note 16)
Output Voltage
TJ = 25C (Note 3)
-25C
TJ
85C
Full Operating Temperature Range
4.975
4.95
4.94
5.0
5.0
5.0
5.025
5.050
5.06
4.95
4.925
4.90
5.0
5.0
5.0
5.05
5.075
5.10
V
V
V
Output Voltage
100
A
IL
100 mA
TJ
TJMAX
4.925
5.0
5.075
4.88
5.0
5.12
V
All Voltage Options
Output Voltage
Temperature Coefficient
(Note 12) (Note 4)
20
50
ppm/C
Line Regulation (Note 14)
6V
Vin
30V (Note 15)
0.03
0.1
0.04
0.2
%
Load Regulation (Note 14)
100
A
IL
100 mA
0.04
0.1
0.1
0.2
%
Dropout Voltage
(Note 5)
IL = 100
A
IL = 100 mA
50
380
80
450
50
380
80
450
mV
mV
Ground Current
IL = 100
A
IL = 100 mA
75
8
120
12
75
8
120
12
A
mA
Current Limit
Vout = 0
160
200
160
200
mA
Thermal Regulation
(Note 13)
0.05
0.2
0.05
0.2
%/W
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LP2950/LP2951
ELECTRICAL CHARACTERISTICS
(Note 2) (Continued)
PARAMETER
CONDITIONS
(Note 2)
LP2950AC
LP2951AC
Min. Typ. Max.
LP2950C
LP2951C
Min. Typ. Max.
Units
Output Noise,
10Hz to 100KHz
CL = 1
F
CL = 200
F
CL = 13.3
F
(Bypass = 0.01
F pins 7 to
1(LP2951))
430
160
100
430
160
100
V rms
V rms
V rms
8-Pin Versions only
LP2951AC
LP2951C
Reference Voltage
1.22
1.235
1.25
1.21
1.235
1.26
V
Reference Voltage
Over Temperature (Note 7)
1.19
1.27
1.185
1.285
V
Feedback Pin Bias Current
40
60
40
60
nA
Reference Voltage Temperature
Coefficient
( Note 12 )
20
50
ppm/C
Feedback Pin Bias Current
Temperature Coefficient
0.1
0.1
nA/C
Error Comparator
Output Leakage Current
V
OH
= 30V
0.01
1
0.01
1
A
Output Low Voltage
Vin = 4.5V
IOL = 400
A
150
250
150
250
mV
Upper Threshold Voltage
(Note 6)
40
60
40
60
mV
Lower Threshold Voltage
(Note 6)
75
95
75
95
mV
Hysteresis
(Note 6)
15
15
mV
Shutdown Input
Input logic Voltage
Low (Regulator ON)
High (Regulator OFF)
2
1.3
0.7
2
1.3
0.7
V
V
Shutdown Pin Input Current
(Note 3)
Vs = 2.4V
Vs = 30V
30
450
50
600
30
450
50
600
A
A
Regulator Output Current in
Shutdown (Note 3)
(Note 11)
3
10
3
10
A
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 V
IN
= (
V
ONOM
+1)V, I
L
= 100
A and C
L
= 1
F for 5V versions and 2.2
F 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 T
A
= T
J
= 25
C
Additional conditions for the 8-pin versions are FEEDBACK tied to V
TAP
, OUTPUT tied to SENSE and V
SHUTDOWN
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
V
IN
= (
V
ONOM
+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/1.235 = 384 mV. Thresholds remain constant
as a percent of V
out
as V
out
is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.
Note 7: V
ref
V
out
(V
in
- 1V), 2.3
V
in
30V, 100
A
I
L
100 mA, T
J
T
JMAX
.
Note 8: The junction-to-ambient thermal resistance are as follows:180
C/W and 160
C/W for the TO-92 (N) 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 (P) and 160
C/W for the molded plastic SO-8 (S). The above thermal resistances for
the N, S and P packages apply when the package is soldered directly to the PCB.
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
ground.
Note 11: V
shutdown
2V, V
in
30V, V
out
=0, Feedback pin tied to 5V
TAP
.
Note 12: Output or reference voltage temperature coefficients defined as the worst case voltage change divided by the total temperature range.
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LP2950/LP2951
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 V
IN
=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 I
L
= 1 mA. For I
L
= 100
A and T
J
= 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: 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 of the part number.
BLOCK DIAGRAM AND TYPICAL APPLICATIONS
LP2950-XX
LP2951-XX
INPUT
OUTPUT
GROUND
ERROR
AMPLIFIER
1.23V
REFERENCE
UNREGULATED DC
V
OUT
I
L
100mA
SEE APPLICATION
HINTS
+
+
+
+
-
INPUT
OUTPUT
GROUND
ERROR
AMPLIFIER
1.23V
REFERENCE
UNREGULATED DC
V
OUT
I
L
100mA
SEE APPLICATION
HINTS
+
+
+
+
-
FEED-
BACK
SHUT-
DOWN
SENSE
V
TAP
ERROR
TO CMOS
OR TTL
+
-
+
330k
4
5
6
2
1
8
7
3
FROM
CMOS
OR TTL
50mV
ERROR DETECTION COMPARATOR
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LP2950/LP2951
TYPICAL PERFORMANCE CHARACTERISTICS
0
40
100
60
160
0
1
2
3
4
5
6
7
8
INPUT VOLTAGE (V)
Quiescent Current
QUIESCENT CURRENT (
A)
125
250
Input Current
25
50
75
100
150
175
200
225
INPUT VOLTAGE (V)
INPUT CURRENT (
A)
5V OUTPUT
-75
0
25 50 75 100 125
5.06
5.0
150
OUTPUT VOLTAGE (V)
Temperature Drift of 3
Representative Units
TEMPERATURE ( C)
5.04
4.98
4.94
-50 -25
0.1
1
10
100
LOAD CURRENT (mA)
GROUND CURRENT (mA)
0.01
0.1
1
10
Quiescent Current
Dropout Characteristics
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
R
L
= 50 k
0
60
120
Input Current
10
20
30
50
70
80
90
100
INPUT VOLTAGE (V)
INPUT CURRENT (mA)
-75
0
25 50 75 100 125
120
90
150
QUIESCENT CURRENT (
A)
Quiescent Current
TEMPERATURE ( C)
100
70
60
-50 -25
I
L
= 100
A
-75
0
25 50 75 100 125
10
150
QUIESCENT CURRENT (mA)
Quiescent Current
TEMPERATURE ( C)
9
8
7
-50 -25
I
L
= 100mA
50
80
110
20
80
140
120
0
2
5
3
8
0
1
2
3
4
5
6
7
8
INPUT VOLTAGE (V)
Quiescent Current
QUIESCENT CURRENT (
A)
1
4
7
6
0
1
2
3
4
5
6
1
2
3
4
5
6
7
8
9 10
0
0
1
2
3
4
5
6
0
1
2
3
4
5
6
7
8
9 10
0
40
110
5.02
4.96
5V OUTPUT
5V OUTPUT
5V OUTPUT
5V OUTPUT
5V OUTPUT
5V OUTPUT
5V OUTPUT
I
L
= 1 mA
I
L
= 100mA
R
L
= 50
R
L
= 50 k
I
L
= 0
V
IN
= 6V
V
IN
= 6V
R
L
= 50
0.2%
R
L
=
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LP2950/LP2951
TYPICAL PERFORMANCE CHARACTERISTICS
(Continued)
-75
0
25 50 75 100 125
170
140
150
SHORT CIRCUIT CURRENT (
m
A)
Short Circuit Current
TEMPERATURE ( C)
150
120
110
-50 -25
-75
0
25 50 75 100 125
600
150
DROPOUT VOLTAGE (mV)
Dropout Voltage
TEMPERATURE ( C)
400
100
0
-50 -25
I
L
= 100mA
100
130
160
-75
0
25 50 75 100 125
2.2
150
MINIMUM OPERATING VOLTAGE (V)
LP2951 Minimum Operating Voltage
TEMPERATURE ( C)
-50 -25
-75
0
25 50 75 100 125
20
150
BIAS CURRENT (nA)
LP2951 Feedback Bias Current
TEMPERATURE ( C)
0
-30
-50 -25
-2.0
-1.5 -1.0
-0.5
0
0.5
-250
50
-50
-150
LP2951 Feedback Pin Current
1.0
FEEDBACK VOLTAGE (V)
FEEDBACK CURRENT (
A)
-200
0
-100
200
400
600
100
mV
800
INPUT
VOLTAGE
Line Transient Response
TIME (
s)
0
8V
4V
0
I
L
= 1mA
V
OUT
= 5V
0.0
0.3 0.4 0.5 0.6 0.7 0.8
2.5
0.9
SINK CURRENT (mA)
LP2951 Comparator Sink Current
OUTPUT LOW VOLTAGE (V)
1.5
0.0
0.1 0.2
0
3
4
5
6
7
8
9
4
ERROR OUTPUT (V)
LP2951 Error Comparator Output
INPUT VOLTAGE (V)
5
2
1
1
2
0
3
6
V
OUT
= 5V
100
A
1mA
10mA
100mA
OUTPUT CURRENT
DROPOUT VOLTAGE (mV)
0
500
Dropout Voltage
500
300
50
400
300
200
100
2.1
2.0
1.9
1.8
1.7
1.6
10
-10
-20
50
mV
-50
mV
6V
OUTPUT VOLTAGE
CHANGE
~
~
~
~
8
7
2.0
1.0
0.5
I
L
= 100
A
T
J
= 25C
T
A
= 125C
T
A
= 25C
T
A
= -55C
PIN 7 DRVEN BY EXTERNAL
SOURCE (REGULATOR RUN
OPEN LOOP)
T
A
= 125C
T
A
= 25C
T
A
= -55C
C
L
= 1
F
HYSTERESIS
50k RESISTOR TO
EXTERNAL 5V SUPPLY
50k
RESISTOR
TO V
OUT
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LP2950/LP2951
TYPICAL PERFORMANCE CHARACTERISTICS
(Continued)
Load Transient Response
TIME (ms)
OUTPUT VOLTAGE
CHANGE (mV)
C
L
= 1
F
0
1
2
3
4
5
100
0
50
150
250
V
OUT
= 5V
2
7
LP2951 Enable Transient
0
2
0
1
3
4
5
6
TIME (
s)
SHUTDOWN PIN
VOLTAGE (V)
0
100 200 300 400 500 600 700
-100
-2
I
L
= 10 mA
200
100
-50
-100
100
mA
A
~
~
~
~
LOAD
CURRENT
Load Transient Response
TIME (ms)
OUTPUT VOLTAGE
CHANGE (mV)
0
4
8
12
16
20
100
-20
0
40
80
60
20
-40
-60
100
mA
A
~
~
LOAD
CURRENT
OUTPUT
VOLTAGE (V)
C
L
= 10
F
V
OUT
= 5V
V
OUT
= 5V
C
L
= 10
F
C
L
= 1
F
V
IN
= 8V
10
100
1K
100K
FREQUENCY (Hz)
OUPUT IMPEDANCE (
)
0.01
10
Output Impedance
2
1
0.05
0.02
10
1
10
4
10
5
90
60
10
6
RIPPLE REJECTION (dB)
Ripple Rejection
FREQUENCY (Hz)
70
40
30
10
2
I
L
= 100
A
20
50
80
V
IN
= 6V
10
3
10
1
10
4
10
5
90
60
10
6
RIPPLE REJECTION (dB)
Ripple Rejection
FREQUENCY (Hz)
70
40
30
10
2
I
L
= 1mA
20
50
80
V
IN
= 6V
10
3
10
1
10
4
10
5
80
50
10
6
RIPPLE REJECTION (dB)
Ripple Rejection
FREQUENCY (Hz)
60
30
20
10
2
I
L
= 50mA
10
40
70
V
IN
= 6V
10
3
FREQUENCY (Hz)
VOLTAGE NOISE SPECTRAL
DENSITY(mV/
Hz)
0.0
3.5
LP2951 Output Noise
2.0
1.5
0.5
10
4
10
5
10
2
10
3
1.0
3.0
2.5
-75
0 25 50 75 100 125
400
200
150
PIN 2 TO PIN 4 RESISTANCE (k
)
LP2951 Divider Resistance
TEMPERATURE ( C)
300
100
-50 -25
0
5
0.1
0.2
0.5
10K
1M
C
L
= 1
F
I
L
= 100mA
C
L
= 220
F
C
L
= 3.3
F
0.01
F
BYPASS
PIN 1 TO
PIN 7
5V OUTPUT
I
L
= 100mA
C
L
= 1
F
V
OUT
= 5V
C
L
= 1
F
V
OUT
= 5V
I
O
= 1 mA
I
O
= 100
A
I
O
= 100mA
V
OUT
= 5V
C
L
= 1
F
I
L
= 0
V
OUT
= 5V
C
L
= 1
F
I
L
= 10mA
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LP2950/LP2951
TYPICAL PERFORMANCE CHARACTERISTICS
(Continued)
-75
0
25 50 75 100 125
1.8
1.2
150
SHUTDOWN TRESHOLD VOLTAGE (V)
Shutdown Treshold Voltage
TEMPERATURE ( C)
1.6
1.0
0.6
-50 -25
1.4
0.8
REGULATOR OFF
0
5
10
15
20
25
0
120
80
40
LP2951 Maximum Rated
Output Current
30
INPUT VOLTAGE (V)
OUTPUT CURRENT (
m
A)
20
100
60
0
5
Thermal Response
0
1
-2
2
4
TIME (
s)
POWER
DISSIPATION (W)
10
20
30
40
50
0
-1
5
15
20
25
30
0
30
OUTPUT VOLTAGE CHANGE (V)
Line Regulation
INPUT VOLTAGE (V)
10
-10
10
I
L
= 100
A
10
-5
5
0
~
~
5
25
20
15
0
5
10
15
20
25
0
120
80
40
LP2950 Maximum Rated
Output Current
30
INPUT VOLTAGE (V)
OUTPUT CURRENT (
m
A)
20
100
60
~
~
OUTPUT VOLTAGE
CHANGE (mV)
1.25W
T
A
= 25 C
T
A
= 50 C
T
A
= 25 C
T
A
= 85 C
T
A
= 85 C
T
JMAX
= 125 C
V
OUT
= 5V
8 PIN MOLDED
DIP SOLDERED
TO PC BOARD
REGULATOR ON
TO-92 PACKAGE
.25"LEADS SOLDERED
TO PC BOARD
T
JMAX
= 125 C
I
L
= 1mA
I
L
= 100
A
T
J
= 150 C
T
J
= 125 C
Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723
LP2950/LP2951
APPLICATION HINTS
External Capacitors
A 1.0
F or greater capacitor is required between output and
ground for stability at output voltages of 5V or more. At lower
output voltages, more capacitance is required (2.2
or more is
recommended for 3V and 3.3V versions). Without this capacitor
the part will oscillate. Most types of tantalum or aluminum
electrolytic works fine here; even film types work but are not
recommended for reasons of cost. Many aluminum types 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 5
or less and
resonant frequency above 500 kHz parameters in the value of the
capacitor. 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
F for
currents below 10 mA or 0.1
F for currents below 1 mA. 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 3.3
F (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
version with external resistors, a minimum load of 1
A is
recommended.
A 1
F tantalum or aluminum electrolytic capacitor should be
placed from the LP2950/LP2951 input to the 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 a
higher value of 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
F 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 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 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.
Figure 1 gives a timing diagram depicting the ERROR signal and
the regulator 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 = 4.75 ).
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.
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
the output is rated to sink 400
A, this sink current adds to
battery drain in a low battery condition. Suggested values range
from 100K to 1M
. The resistor is not required if this output is
unused.
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 V
TAP
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:
V
out
= V
REF
(1 + R
1
/ R
2
)+ I
FB
R
1
where V
REF
is the nominal 1.235 reference voltage and I
FB
is the
feedback pin bias current, nominally -20 nA. The minimum
recommended load current of 1
A forces an upper limit of 1.2
M
on value of R
2
, if the regulator must work with no load (a
condition often found in CMOS in standby) I
FB
will produce a 2%
typical error in V
OUT
which may be eliminated at room
temperature by trimming R
1
. For better accuracy, choosing R2 =
100k reduces this error to 0.17% while increasing the resistor
program current by 12
A. Since the LP2951 typically draws 60
A at no load with Pin 2 open-circuited, this is a small price to
pay.
Reducing Output Noise
In reference applications it may be an 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 that noise can be reduced on the 3
lead LP2950 but is relatively inefficient, as increasing the
capacitor from 1
F to 220
F only decreases the noise from 430
V to 160
V rms for a 100 kHz bandwidth at 5V output.
Noise could also be reduced fourfold by a bypass capacitor across
R
1
, since it reduces the high frequency gain from 4 to unity. Pick
C
BYPASS
1 / 2
R
1
200 Hz
or about 0.01
F. When doing this, the output capacitor must be
increased to 3.3
F to maintain stability. These changes reduce
the output noise from 430
V to 100
V 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.
Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723
LP2950/LP2951
APPLICATION HINTS (Continued)
OUTPUT
VOLTAGE
ERROR*
INPUT
VOLTAGE
4.75V
5V
1.3V
R
1
ERROR*
ERROR
OUPUT
**SHUTDOWN
INPUT
GND
FB
V
OUT
V
REF
R
2
SD
1.23V
7
4
3
8
1
5
+V
IN
+V
IN
V
OUT
1.2
30V
3.3
F
.01
F
+
*
100k
LP2951
FIGURE 1. ERROR Output Timing
FIGURE 2. Adjustable Regulator
*When
V
IN
1.3V the error flag pin becomes a high impedance,
and the error flag voltage rises to its pull-up voltage. Using V
out
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 drive 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.
*See Application Hints.
V
out
= V
REF
(1 + R
1
/ R
2
)
**Drive with TTL- high to shut down. Ground or leave if shutdown
feature is not used.
Note: Pins 2 and 6 are left open.
TYPICAL APPLICATIONS
300 mA Regulator with 0.75 Dropout
Wide Input Voltage Range Current Limiter
UNREGULATED
INPUT
LOAD
50mA TO
300mA
GND
FB
OUT
IN
4
7
6
2
1
8
V
TAP
LP2951
2N5432 (2)
SENSE
5V OUTPUT
4.7
F
27
k
330
ERROR
ERROR
OUPUT
SHUTDOWN
INPUT
GND
FB
V
OUT
SD
7
4
3
8
1
5
+V
IN
+V
IN
LP2951
*V
OUT
V
*Minimum Input-Output voltage ranges from 40mV to 400mV, depending on load
current. Current limit is typically 160 mA
Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723
LP2950/LP2951
TYPICAL APPLICATIONS
(Continued)
Low Drift Current Source
5Volt Current Limiter
SHUTDOWN
INPUT
GND
FB
V
OUT
SD
7
4
3
8
1
V
IN
+V = 2
LP2951
LOAD
30V
I
L
R
1%
1
F
0.1
F
+
GND
V
OUT
+V
IN
5V BUS
LP2950 -5.0
*V
OUT
5V
1
F
*Minimum Input-Output voltage ranges from 40mV to 400mV, depending on load
current. Current limit is typically 160 mA
5V Regulator with 2.5V Sleep Function
Open Circuit Detector for 4 to 20mA Current Loop
ERROR
ERROR
OUPUT
SHUTDOWN
INPUT
GND
FB
V
OUT
SD
7
4
3
8
1
5
+V
IN
+V
IN
LP2951
C - MOS
GATE
200
k
100
k
100
k
3.3
F
470
k
47
k
*SLEEP
INPUT
1%
1%
100
pF
2N3906
+V
OUT
+
GND
V
OUT
+V
IN
+5V
LP2951
*OUTPUT
0.1
F
FB
4.7k
360
1N4001
1N457
4
8
1
4
MIN. VOLTAGE
4V
20mA
7
2
1
5
4
Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723
LP2950/LP2951
TYPICAL APPLICATIONS
(Continued)
2 Ampere Low Dropout Regulator
Regulator with Early Warning and Auxiliary Output
ERROR
ERROR
FLAG
CURRENT
LIMIT SECTION
GND
FB
V
OUT
SD
1
4
3
8
5
7
+V
IN
+V
IN
= V
OUT
+.5V
LP2951
+V
OUT
@ 2A
R
1
R
2
10k
100
F
4.7
TANT.
+
+
1%
220
.033
20k
4.7M
2N3906
0.05
680
470
MJE2955
ERROR
GND
FB
V
OUT
5
4
8
1
6
+V
IN
LP2951
#1
V
TAP
7
ERROR
GND
FB
V
OUT
4
8
6
+V
IN
LP2951
#2
V
TAP
3
SD
7
SENSE
2
5
RESET
1
F
20
+V
IN
D
1
D
2
3.6V
NICAD
27 k
2.7M
330 k
1
F
D
4
Q
1
MAIN 5V OUTPUT
P
V
DD
2
D
3
5V MEMORY
SUPPLY
EARLY WARNING
SENSE
+
+
VOUT = 1.23V(1+R1/R2)
For 5V V
OUT
, use internal resistors. Wire pin 6 to 7 and pin 2 to +V
OUT
Buss.
Early warning flag on low input voltage
Main output latches off at lower input voltages
Battery backup on auxiliary output
Operation: Reg.#1's V
OUT
is programmed one diode drop above 5V. It's error flag
becomes active when V
IN
5.7V. When V
IN
drops below 5.3V, the error flag of
Reg.#2 becomes active and via Q1 latches the main output off. When V
IN
again
exceeds 5.7V Reg.#1 is back in regulation and the early warning signal rises,
unlatching Reg.#2 via D3.
1A Regulator with 1.2V Dropout
Latch Off When Error Flag Occurs
OUTPUT
5V 1% @
0 TO 1A
GND
FB
OUT
IN
4
7
6
1
2
8
V
TAP
LP2951
SUPERTEX
VP12C
SENSE
0.002
F
2
k
10
k
1
0.01
F
220
F
1
F
+
I
Q
400
A
UNREGULATED
INPUT
R
1
ERROR
GND
FB
V
OUT
R
2
SD
7
4
3
8
1
5
+V
IN
+V
IN
V
OUT
1
F
+
470k
LP2951
470k
RESET
Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723
LP2950/LP2951
PACKAGE DIMENSIONS
inches (millimeters) unless otherwise noted.
3 LEAD TO-92 PLASTIC PACKAGE (N)
8 LEAD SOIC PLASTIC PACKAGE (S)
0.1400.010
(3.5560.127)
0.0600.010
(1.5240.254)
0.0150.002
(0.3810.051)
0.0160.003
(0.4060.076)
0.0500.005
(1.2700.127)
0.0600.005
(1.5240.127)
DIA
0.1800.005
(4.5720.127)
0.1800.005
(4.5720.127)
0.050
(1.270)
MAX
0.500
(12.70)
MIN
UNCONTROLLED
LEAD DIMENSIONS
10
NOM
5 NOM
N (TO-92 ) AMS DRW# 042391
0.90
(2.286)
NOM
0-8 TYP
0.010-0.020
(0.254-0.508)
S (SO-8 ) AMS DRW# 042293
x 45
0.016-0.050
(0.406-1.270)
0.008-0.010
(0.203-0.254)
0.004-0.010
(0.101-0.254)
0.014-0.019
(0.355-0.483)
0.053-0.069
(1.346-1.752)
0.050
(1.270)
TYP
0.150-0.157**
(3.810-3.988)
0.228-0.244
(5.791-6.197)
0.189-0.197*
(4.801-5.004)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
1
2
3
4
8
7
6
5
Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723
LP2950/LP2951
PACKAGE DIMENSIONS
inches (millimeters) unless otherwise noted (Continued).
8 LEAD PLASTIC DIP PACKAGE (P)
0.045-0.065
(1.143-1.651)
0.2550.015*
(6.4770.381)
0.400*
(10.160)
MAX
1
2
3
4
8
7
6
5
0.1300.005
(3.3020.127)
0.0180.003
(0.4570.076)
0.1000.010
(2.5400.254)
(
8.255
)
+0.635
-0.381
0.325 +0.025
-0.015
0.009-0.015
(0.229-0.381)
0.300-0.325
(7.620-8.255)
0.065
(1.651)
TYP
0.005
(0.127)
MIN
0.125
(3.175)
MIN
0.015
(0.380)
MIN
*DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTUSIONS.
MOLD FLASH OR PROTUSIONS SHALL NOT EXCEED 0.010" (0.254mm)
P (8L PDIP ) AMS DRW# 042294
PDF 
ZIP