Advanced Monolithic Systems LP2950CS-3.3, LP2950CS-3.0, LP2950CP-3.3, LP2950CN-3.3, LP2950CN-3.0 Datasheet

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

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 (1µµF) 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.75µA), 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

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

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 (TJ) (Note 8)

LP2950AC-XX, LP2950C-XX
LP2951AC-XX, LP2951C-XX

-40°C to +125°C

ELECTRICAL CHARACTERISTICS at V

s

=Vout+1V, Ta=25°C, 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 = 25°C (Note 3)

-25°C ≤TJ ≤85°C
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 µA ≤IL ≤100 mA
TJ ≤T

JMAX

2.958

3.0

3.042 2.928

3.0

3.072

V

3.3 V Versions (Note 16)
Output Voltage

TJ = 25°C (Note 3)

-25°C ≤TJ ≤85°C
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 µA ≤IL ≤100 mA
TJ ≤T

JMAX

3.254

3.3

3.346 3.221

3.3

3.379

V

5 V Versions (Note 16)
Output Voltage

TJ = 25°C (Note 3)

-25°C ≤TJ ≤85°C
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 µA ≤IL ≤100 mA
TJ ≤T

JMAX

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 µA ≤IL ≤ 100 mA

0.04 0.1 0.1 0.2 %

Dropout Voltage
(Note 5)

IL = 100µ A
IL = 100 mA

50

380

80

450

50

380

80

450

mV
mV

Ground Current

IL = 100 µA
IL = 100 mA

75

8

120

12

75

8

120

12

µA

mA

Current Limit

V

out

= 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 = 1µF
CL = 200 µF
CL = 13.3 µF
(Bypass = 0.01 µF pins 7 to

1(LP2951))

430
160
100

430
160
100

µV rms
µV rms
µV 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

µA

Output Low Voltage

Vin = 4.5V
IOL = 400µA

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

µA
µA

Regulator Output Current in
Shutdown (Note 3)

(Note 11) 3 10 3 10

µA

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, IL = 100 µA and CL = 1 µF 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 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 ≤Vout

≤ (Vin - 1V), 2.3 ≤Vin≤30V, 100µA≤IL≤ 100 mA, TJ ≤ 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, Vin ≤ 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.

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

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 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: 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

IL≤ 100mA

SEE APPLICATION

HINTS

+

+

+

+

-

INPUT OUTPUT

GROUND

ERROR
AMPLIFIER

1.23V
REFERENCE

UNREGULATED DC

V

OUT

I

L

≤

100mA

SEE APPLICATION

HINTS

+

+

+

+

-

FEED­BACK

SHUT-

DOWN

SENSE

V

TAP

ERROR

TO CMOS
OR TTL

+

-

+

330k

Ω

4

5

6

2

187

3

FROM
CMOS

OR TTL

50mV

ERROR DETECTION COMPARATOR

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

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 (µA)

125

250

Input Current

25

50

75

100

150

175

200

225

INPUT VOLTAGE (V)

INPUT CURRENT (µA)

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)

RL= 50 kΩ

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 (

µ

A)

Quiescent Current

TEMPERATURE (° C)

100

70

60

-50 -25

IL= 100µA

-75

0 25 50 75 100 12510150

QUIESCENT CURRENT (mA)

Quiescent Current

TEMPERATURE (° C)

9

8

7

-50 -25

IL= 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 (µA)

1

4

7
6

0

1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 100

0

1

2

3

4

5

6

0

1 2 3 4 5 6 7 8 9 100

40

110

5.02

4.96

5V OUTPUT

5V OUTPUT5V OUTPUT 5V OUTPUT

5V OUTPUT

5V OUTPUT

5V OUTPUT

IL= 1 mA

IL= 100mA

RL= 50Ω

RL= 50 kΩ

IL= 0

VIN= 6V

VIN= 6V

RL= 50Ω

0.2%

RL= ∞

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LP2950/LP2951

TYPICAL PERFORMANCE CHARACTERISTICS (Continued)

-75 0 25 50 75 100 125

170

140

150

SHORT CIRCUIT CURRENT (mA)

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

IL= 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 (µA)

-200

0

-100

200 400 600

100
mV

800

INPUT

VOLTAGE

Line Transient Response

TIME (µs)

0

8V

4V

0

IL= 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 0.20 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

100µA 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

IL= 100µA

TJ = 25°C

TA = 125°C

TA = 25°C

TA = -55°C

PIN 7 DRVEN BY EXTERNAL
SOURCE (REGULATOR RUN

OPEN LOOP)

TA = 125°C

TA = 25°C

TA = -55°C

CL= 1µF

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)

CL= 1 µF

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 (µs)

SHUTDOWN PIN

VOLTAGE (V)

0 100 200 300 400 500 600 700-100

-2

IL= 10 mA

200

100

-50

-100

100

mA

µ

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

µ

A

~

~

LOAD

CURRENT

OUTPUT

VOLTAGE (V)

CL= 10 µF

V

OUT

= 5V

V

OUT

= 5V

CL= 10 µF

CL= 1 µF

V

IN

= 8V

10 100 1K 100K

FREQUENCY (Hz)

OUPUT IMPEDANCE (

Ω

)

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

IL= 100µA

20

50

80

VIN= 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

IL= 1mA

20

50

80

VIN= 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

IL= 50mA

10

40

70

VIN= 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

Ω

)

LP2951 Divider Resistance

TEMPERATURE (° C)

300

100

-50 -25

0

5

0.1

0.2

0.5

10K 1M

CL= 1 µF

IL= 100mA

CL= 220 µF

CL= 3.3 µF

0.01 µF
BYPASS
PIN 1 TO
PIN 7

5V OUTPUT

IL= 100mA

CL= 1µF

V

OUT

= 5V

CL= 1 µF

V

OUT

= 5V

IO= 1 mA

IO= 100µA

IO= 100mA

V

OUT

= 5V

CL= 1 µF

IL= 0

V

OUT

= 5V

CL= 1 µF

IL= 10mA

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

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 (mA)

20

100

60

0

5

Thermal Response

0

1

-2

2

4

TIME (µs)

POWER

DISSIPATION (W)

10 20 30 40 500

-1

5 15 20 25

30

0

30

OUTPUT VOLTAGE CHANGE (V)

Line Regulation

INPUT VOLTAGE (V)

10

-10
10

IL= 100µA

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 (mA)

20

100

60

~

~

OUTPUT VOLTAGE

CHANGE (mV)

1.25W

TA= 25° C

TA= 50° C

TA= 25° C

TA= 85° C

TA= 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

IL= 1mA

IL= 100µA

TJ = 150° C

TJ = 125° C

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LP2950/LP2951

APPLICATION HINTS

External Capacitors

A 1.0 µF 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 (2.2µ 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 Ω 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 µF for
currents below 10 mA or 0.1 µF 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 3.3µF (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
version with external resistors, a minimum load of 1µA is
recommended.
A 1µF 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 µF 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 400µA, this sink current adds to
battery drain in a low battery condition. Suggested values range
from 100K to 1MΩ. The resistor is not required if this output is
unused.

Programming the Output Voltage (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 + R1/ R2)+ IFBR

1

where V

REF

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 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 V

OUT

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 by 12 µA. Since the LP2951 typically draws 60
µA 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 µF to 220 µF only decreases the noise from 430
µV to 160 µV rms for a 100 kHz bandwidth at 5V output.
Noise could also be reduced fourfold by a bypass capacitor across
R1, since it reduces the high frequency gain from 4 to unity. Pick

C

BYPASS

≅ 1 / 2πR1 × 200 Hz

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.

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

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

74

3

8

15

+V

IN

+V

IN

V

OUT

1.2 30V

3.3µF

.01

µF

+*

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 + R1/ R2)

**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

GNDFB

OUTIN

47

6

2

18

V

TAP

LP2951

2N5432 (2)

SENSE

5V OUTPUT

4.7µF

27kΩ

330Ω

ERROR

ERROR
OUPUT

SHUTDOWN
INPUT

GND FB

V

OUT

SD

74

3

8

15

+V

IN

+V

IN

LP2951

*V

OUT

≈ V

ΙΝ

*Minimum Input-Output voltage ranges from 40mV to 400mV, depending on load
current. Current limit is typically 160 mA

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

LP2950/LP2951

TYPICAL APPLICATIONS (Continued)

Low Drift Current Source 5Volt Current Limiter

SHUTDOWN
INPUT

GND FB

V

OUT

SD

74

3

8

1

V

IN

+V = 2

LP2951

LOAD

30V

I

L

R

1%

1µF

0.1µF

+

GND

V

OUT

+V

IN

5V BUS

LP2950 -5.0

*V

OUT

≈ 5V

1µF

*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

74

3

8

15

+V

IN

+V

IN

LP2951

C - MOS
GATE

200kΩ

100kΩ

100kΩ

3.3µF

470kΩ

47kΩ

*SLEEP

INPUT

1%

1%

100pF

2N3906

+V

OUT

+

GND

V

OUT

+V

IN

+5V

LP2951

*OUTPUT

0.1µF

FB

4.7kΩ

360

1N4001

1N457

4

8

1

4

MIN. VOLTAGE ≈ 4V

20mA

7

2

1

5

4

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

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

14

3

8

5

7

+V

IN

+V

IN

= V

OUT

+.5V

LP2951

+V

OUT

@ 2A

R

1

R

2

10kΩ

100µF

4.7

TANT.

++

1%

220

.033

20kΩ

4.7MΩ

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

1µF

20

+V

IN

D

1

D

2

3.6V
NICAD

27 kΩ

2.7MΩ

330 kΩ

1µF

D

4

Q

1

MAIN 5V OUTPUT

µP

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 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.

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

0.002µ

F

2kΩ

10kΩ

1ΜΩ

0.01µ

F

220µ

F

1µ

F

+

IQ ≅

400µA

UNREGULATED

INPUT

R

1

ERROR

GND

FB

V

OUT

R

2

SD

7

4

3

8

15

+V

IN

+V

IN

V

OUT

1µF

+

470kΩ

LP2951

470kΩ

RESET

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

LP2950/LP2951

PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted.

3 LEAD TO-92 PLASTIC PACKAGE (N)

8 LEAD SOIC PLASTIC PACKAGE (S)

0.140±0.010

(3.556±0.127)

0.060±0.010

(1.524±0.254)

0.015±0.002

(0.381±0.051)

0.016±0.003

(0.406±0.076)

0.050±0.005

(1.270±0.127)

0.060±0.005

(1.524±0.127)

DIA

0.180±0.005

(4.572±0.127)

0.180±0.005

(4.572±0.127)

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. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]

LP2950/LP2951

PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted (Continued).

8 LEAD PLASTIC DIP PACKAGE (P)

0.045-0.065

(1.143-1.651)

0.255±0.015*

(6.477±0.381)

0.400*

(10.160)

MAX

1 2 3 4

8 7 6 5

0.130±0.005

(3.302±0.127)

0.018±0.003

(0.457±0.076)

0.100±0.010

(2.540±0.254)

(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