Datasheet LP2951-02BN, LP2951-02BM, LP2951-4.8BM, LP2951-03BN, LP2951-03BM Datasheet (MICREL)

LP2950/2951 Micrel

LP2950/2951

100mA Low-Dropout Voltage Regulator

General Description

The LP2950 and LP2951 are micropower voltage regulators
with very low dropout voltage (typically 40mV at light loads
and 380mV at 100mA), and very low quiescent current (75µA
typical). The quiescent current of the LP2950/LP2951
increases only slightly in dropout, thus prolonging battery life.
This feature, among others, makes the LP2950 and LP2951
ideally suited for use in battery-powered systems.

Available in a 3-Pin TO-92 package, the LP2950 is pin­compatible with the older 5V regulators. Additional system
functions, such as programmable output voltage and logic­controlled shutdown, are available in the 8-pin DIP and 8-pin
SOIC versions of the LP2951.

Applications

• Automotive Electronics

• Voltage Reference

• Avionics

Block Diagram and Pin Configurations

UNREGULATED DC

+

INPUTFEEDBACK

Features

• High accuracy 5V, guaranteed 100 mA output

• Extremely low quiescent current

• Low-dropout voltage

• Extremely tight load and line regulation

• Very low temperature coefficient

• Use as regulator or reference

• Needs only 1µF for stability

• Current and thermal limiting

LP2951 Ver sions Only

• Error flag warns of output dropout

• Logic-controlled electronic shutdown

• Output programmable from 1.24 to 29V

5V

150 mA

187

OUTPUT

MAX.

3

FROM
CMOS

OR TTL

321

OUTPUT INPUT

GROUND

TO-92 Plastic Package Bottom View

SHUT­DOWN

(BZ)

3

60 mV

1.23 V
REF.

LP2950 and LP2951 Block Diagram

+
–

ERROR

AMPLIFIER

+

+

ERROR

–

+

(Pin Numbers Refer to LP2951)

DETECTION

COMPARATOR

182

kΩ

60
kΩ

OUTPUT

SENSE

SHUTDOWN

GROUND

2

SENSE

6

5V TAP

ERROR

GROUND

1
2

3
4

DIP and SO Packages

(BN and BM)

+

5

4

1.5 µF

8
7

6
5

330

kΩ

TO CMOS

OR TTL

INPUT

FEEDBACK

5V TAP
ERROR

See MIC2950 for a part with 1) higher output (150 mA), 2) transient protection (60V), and 3) reverse input protection to –20V)

February 1999 3-35

LP2950/2951 Micrel

Additional features available with the LP2951 also include an
error flag output that warns of a low output voltage, which is
often due to failing batteries on the input. This may also be
used as a power-on reset. A logic-compatible shutdown input
is also available which enables the regulator to be switched on
and off. This part may also be pin-strapped for a 5V output,
or programmed from 1.24V to 29V with the use of two external
resistors.

The LP2950 is available as either an -02 or -03 version. The

-02 and -03 versions are guaranteed for junction temperatures

Ordering Information

Part Number Voltage Temperature Range* Package Accuracy

LP2950-02BZ 5.0V –40°C to +125°C 3-Pin TO-92 plastic 0.5%
LP2950-03BZ 5.0V –40°C to +125°C 3-Pin TO-92 plastic 1.0%
LP2951-02BM 5.0V –40°C to +125°C 8-Pin SOIC 0.5%
LP2951-03BM 5.0V –40°C to +125°C 8-Pin SOIC 1.0%
LP2951-02BN 5.0V –40°C to +125°C 8-Pin Plastic DIP 0.5%

from –40°C to +125°C; the -02 version has a tighter output and
reference voltage specification range over temperature. The
LP2951 is available as an -02 or -03 version.

The LP2950 and LP2951 have a tight initial tolerance (0.5%
typical), a very low output voltage temperature coefficient
which allows use as a low-power voltage reference, and
extremely good load and line regulation (0.05% typical). This
greatly reduces the error in the overall circuit, and is the result
of careful design techniques and process control.

LP2951-03BN 5.0V –40°C to +125°C 8-Pin Plastic DIP 1.0%
LP2951-4.8BM 4.85V –40°C to +125°C 8-Pin SOIC 1.0%
* Junction temperatures

Absolute Maximum Ratings

If Military/Aerospace specified devices are required, contact your local
Micrel representative/distributor for availability and specifications.

Power dissipation Internally Limited
Lead Temperature (Soldering, 5 seconds) 260°C
Storage Temperature Range –65°C to +150°C
Operating Junction Temperature Range (Note 8)

LP2950, LP2951 –40°C to +125°C

Input Supply Voltage –0.3V to +30V
Feedback Input Voltage (Notes 9 and 10) –1.5V to +30V
Shutdown Input Voltage (Note 9) –0.3V to +30V
Error Comparator Output Voltage (Note 9) –0.3V to +30V
ESD Rating is to be determined.

3-36 February 1999

LP2950/2951 Micrel

Electrical Characteristics Note 1 T

= 25°C except as noted.

A

Parameter Condition Min Typ Max Units

Output Voltage LP295x-02 (±0.5%) 4.975 5.000 5.025 V
TJ = 25°C

LP295x-03 (±1%) 4.950 5.000 5.050 V
LP2951-4.8 (±1%) 4.802 4.850 4.899 V

Output Voltage LP295x-02 (±0.5%) 4.950 5.050 V
–25°C ≤ TJ ≤ +85°C

LP295x-03 (±1%) 4.925 5.075 V
LP2951-4.8 (±1%) 4.777 4.872 V

Output Voltage LP295x-02 (±0.5%), –40°C to +125°C 4.940 5.060 V
Over Full Temperature Range

LP295x-03 (±1%), –40°C to +125°C 4.900 5.100 V
LP2951-4.8 (±1%), –40°C to +125°C 4.753 4.947 V

Output Voltage LP295x-02 (±0.5%), 100µA ≤ IL ≤ 100mA, TJ ≤ T
Over Load Variation

LP295x-03 (±1%), 100µA ≤ IL ≤ 100mA, TJ ≤ T
LP2951-4.8 (±1%), 100µA ≤ IL ≤ 100mA, TJ ≤ T

J(max)

J(max)

J(max)

4.930 5.070 V

4.880 5.120 V

4.733 4.967 V

Output Voltage LP295x-02 (±0.5%), Note 12 20 100 ppm/°C
Temperature Coefficient

LP295x-03 (±1%), Note 12 50 150 ppm/°C
LP2951-4.8 (±1%), Note 12 50 150 ppm/°C

Line Regulation LP295x-02 (±0.5%), Notes 14, 15 0.03 0.10 %

0.20 %

LP295x-03 (±1%), Notes 14, 15 0.04 0.20 %

0.40 %

LP2951-4.8 (±1%), Notes 14, 15 0.04 0.20 %

0.40 %

Load Regulation LP295x-02 (±0.5%), Note 14, 100µA ≤ I

≤ 100mA 0.04 0.10 %

L

0.20 %

LP295x-03 (±1%), Note 14, 100µA ≤ I

LP2951-4.8 (±1%), Note 14, 100µA ≤ I

≤ 100mA 0.10 0.20 %

L

≤ 100mA 0.10 0.20 %

L

0.30 %

0.30 %

Dropout Voltage Note 5, I

= 100µA5080mV

L

150 mV

Note 5, I

= 100mA 380 450 mV

L

600 mV

Ground Current I

= 100µA 100 150 µA

L

200 µA

= 100mA 8 12 mA

I

Dropout Current V

L

= 4.5V, IL = 100µA 180 250 µA

IN

14 mA

310 µA

3

February 1999 3-37

LP2950/2951 Micrel

Parameter Condition Min Typ Max Units

Current Limit V

Thermal Regulation Note 13 0.05 0.20 %/W
Output Noise 10Hz to 100kHz, CL = 1µF 430 µV

Reference Voltage LP295x-02 (±0.5%) 1.220 1.235 1.250 V

Reference Voltage LP295x-02 (±0.5%), Note 7 1.190 1.270 V

Feedback Bias Current 20 40 nA

Reference Voltage LP295x-02 (±0.5%), Note 12 20 ppm/°C

Feedback Bias Current 0.1 nA/°C
Temperature Coefficient

Output Leakage Current V

Output Low Voltage (Flag) V

Upper Threshold Voltage Note 6 40 60 mV

Lower Threshold Voltage Note 6 75 95 mV

Hysteresis Note 6 15 mV
Input Logic Voltage LP295x-02 (±0.5%) 1.3 V

= 0V 160 200 mA

OUT

220 mA

RMS

10Hz to 100kHz, CL = 200µF 160 µV
10Hz to 100kHz, CL = 3.3µF, 100 µV

RMS
RMS

0.01µF bypass Feedback to Output

1.200 1.260 V

LP295x-03 (±1%) 1.210 1.235 1.260 V

1.200 1.270 V

LP2951-4.8 (±1%) 1.210 1.235 1.260 V

1.200 1.270 V

LP295x-03 (±1%), Note 7 1.185 1.285 V
LP2951-4.8 (±1%), Note 7 1.185 1.285 V

60 nA

LP295x-03 (±1%), Note 12 50 ppm/°C
LP2951-4.8 (±1%), Note 12 50 ppm/°C

= 30V 0.01 1.00 µA

OH

2.00 µA

= 4.5V, IOL = 200µA 150 250 mV

IN

400 mV

25 mV

140 mV

Low 0.7 V
High 2.0 V

LP295x-03 (±1%) 1.3 V

Low 0.7 V
High 2.0 V

LP2951-4.8 (±1%) 1.3 V

Low 0.7 V
High 2.0 V

3-38 February 1999

LP2950/2951 Micrel

Parameter Condition Min Typ Max Units

Shutdown Input Current V

SHUTDOWN

V

SHUTDOWN

Regulator Output Current Note 11 3 10 µA
in Shutdown 20 µA

Note 1: Boldface limits apply at temperature extremes.
Note 2: Unless otherwise specified all limits guaranteed for TJ = 25°C, VIN = 6V, IL = 100µA and CL = 1µF. Additional conditions for the 8-pin versions

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 100mV below its nominal value measured at 1V

Note 6: Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage

Note 7: V
Note 8: The junction-to-ambient thermal resistance of the TO-92 package is 180°C/W with 0.4” leads and 160°C/W with 0.25” leads to a PC board.

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-

Note 11:V
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

Note 14: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating

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

are Feedback tied to 5V Tap and Output tied to Output Sense (V

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.

measured at 6V input. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = V
(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 = 384mV. Thresholds remain constant as a percent of V
typically 5% below nominal, 7.5% guaranteed.

≤ V

REF

The thermal resistance of the 8-pin DIP package is 105°C/W junction-to-ambient when soldered directly to a PC board. Junction-to-ambient
thermal resistance for the SOIC (M) package is 160°C/W.

clamped to ground.

SHUTDOWN

regulation effects. Specifications are for a 50mA load pulse at VIN = 30V (1.25W pulse) for t = 10ms.

effects are covered in the specification for thermal regulation.

0.2%. See Typical Performance Characteristics for line regulation versus temperature and load current.

≤ (VIN – 1 V), 2.3V ≤ VIN ≤ 30V, 100µA < IL ≤ 100mA, TJ ≤ T

OUT

≥ 2V, VIN ≤ 30 V, V

OUT

= 2.4V 30 50 µA

= 30V 450 600 µA

= 5V) and V

OUT

= 0, with Feedback pin tied to 5V Tap.

JMAX

OUT

as V

.

SHUTDOWN

≤ 0.8V.

is varied, with the dropout warning occurring at

OUT

100 µA

750 µA

/V

REF

=

OUT

3

February 1999 3-39

LP2950/2951 Micrel

Typical Performance Characteristics

Quiescent Current Dropout Characteristics

10

6

5

1

4

R = 50k

L

3

0.1

2

1

GROUND PIN CURRENT (mA)

0.01

0.1 1 10 150

OUTPUT VOLTAGE (VOLTS)

0

012345 6

LOAD CURRENT (mA) INPUT VOLTAGE (VOLTS)

Output Voltage vs.
Temperature of 3

160
150
140
130
120
110
100

90
80
70
60
50
40
30

INPUT CURRENT (mA)

20
10

0

012345678910

R = 50

L

Ω

Representative UnitsInput Current

5.06

5.04

5.02

5.0

4.98

4.96

OUTPUT VOLTAGE (V)

4.94

-75 -50 -25 0 25 50 75100125 150

Ω

R = 50

L

0.2%

Input Current

250
225
200
175

R = 50k

L

Ω

150
125

R =

Ω

100

∞

L

75
50

INPUT CURRENT (µA)

25

0

012345678910

INPUT VOLTAGE (VOLTS)

Ground Current

320
280
240
200

160
120

I = 1 mA

L

I = 0

L

80
40

GROUND CURRENT (µA)

0

012345678

INPUT VOLTAGE (VOLTS)TEMPERATURE (°C)INPUT VOLTAGE (VOLTS)

240

220

V = 6V

IN

I = 100 µA

L

200

180

QUIESCENT CURRENT (µA)

-75-50 -25 0 25 50 75 100 125 150
TEMPERATURE (°C) TEMPERATURE (°C) INPUT VOLTAGE (V)

170
160

150
140
130
120
110
100

SHORT CIRCUIT CURRENT (mA)

-75-50 -25 0 25 50 75 100 125 150
TEMPERATURE (°C) TEMPERATURE (°C) OUTPUT CURRENT

16

Ground CurrentGround CurrentQuiescent Current

16
14

12

12

V = 6V

IN

I = 100 mA

L

8

GROUND CURRENT (mA)

4

-75 -50 -25 0 25 50 75 100125150

Drop-out VoltageShort Circuit Current Drop-out Voltage

600
500

400

I = 100 mA

L

10

8
6
4
2

GROUND CURRENT (mA)

0

012345678

500

400

300

300

100

50

DROP-OUT VOLTAGE (mV)

0

-75 -50 -25 0 25 50 75 100125150

I = 100 µA

L

200

T = 25 °C

J

100

DROP-OUT VOLTAGE (mV)

0

100 µA 1 mA 10 mA 100 mA

I = 100 mA

L

3-40 February 1999

LP2950/2951 Micrel

LP2951
Minimum Operating Voltage

2.2

2.1

2.0

1.9

1.8

1.7

1.6

-75 -50 -25 0 25 50 75 100125 150

MINIMUM OPERATING VOLTAGE (V)

TEMPERATURE (°C) FEEDBACK VOLTAGE (V)

LP2951
Error Comparator Output

8

V = 5V

6

4

2

0

COMPARATOR OUTPUT (V)

-2

012345

OUT

HYSTERESIS

PULLUP RESISTOR TO
SEPARATE 5V SUPPLY

LP2951
Feedback Bias Current

20

10

0

-10

-20

BIAS CURRENT (nA)

-30

-75 -50 -25 0 25 50 75 100125 150
TEMPERATURE (°C)

LP2951
Comparator Sink Current

2.5
T = 125°C

2.0

1.5

1.0

0.5

SINK CURRENT (mA)

0.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

A

T = 25°C

A

T = -55°C

A

LP2951
Feedback Pin Current

50

PIN 7 DRIVEN BY EXTERNAL
SOURCE (REGULATOR RUN

0

OPEN LOOP)

-50
T = 125°C

A

-100

-150

-200

FEEDBACK CURRENT (µA)

-250

-2.0 -1.5 -1.0 -0.5 0 0.5 1.0

Line Transient Response

100
mV

50

mV

0

CHANGE

-50

mV

OUTPUT VOLTAGE

8V

6V

INPUT

4V

VOLTAGE

0 200 400 600 800

T = 25°C

A

T = –55°C

A

TIME (µs)OUTPUT LOW VOLTAGE (V)INPUT VOLTAGE (V)

C = 1 µF

L

I = 1 mA

L

V = 5V

OUT

3

250
200

150
100

50

0

CHANGE (mV)

-50

OUTPUT VOLTAGE

-100
100

mA

100

LOAD

µA

CURRENT

012345

C = 1 µF

L

V = 5V

OUT

TIME (ms) TIME (ms)

10

I = 100 µA

0

5

I = 1 mA

2

0

1

0.5

0.2

0.1

0.05

0.02

OUTPUT IMPEDANCE (OHMS)

0.01

10 100 1K 10K 100K 1M

FREQUENCY (Hz) FREQUENCY (Hz)

I = 100 mA

0

V = 5V

OUT

C = 1 µF

L

Load Transient ResponseLoad Transient Response

80
60
40
20

0

-20

CHANGE (mV)

-40

OUTPUT VOLTAGE

-60

100

mA

100

LOAD

µA

CURRENT

0 4 8 12 16 20

C = 10 µF

L

V = 5V

OUT

Ripple RejectionOutput Impedance

90
80
70
60
50

40

C = 1 µF

L

V = 6V

IN

30

V = 5V

RIPPLE REJECTION (dB)

OUT

20

1346

2

10 10

I = 0

L

I = 100 µA

L

LP2951
Enable Transient

7
6

5
4

OUTPUT

3

VOLTAGE (V)

2
1
0
2
0

-2

SHUTDOWN

-100 0 100 200 300 400 500 600 700

PIN VOLTAGE (V)

L = 1 µF

L

C = 10 µF

L

TIME (µs)

I = 10 mA

L

V = 8V

IN

V = 5V

OUT

Ripple Rejection

90
80
70

I = 1 mA

L

60
50
40
30

RIPPLE REJECTION (dB)

20

10101010

123456

10 10

FREQUENCY (Hz)

C = 1 µF
V = 6V
V = 5V

I = 10 mA

L

L
IN
OUT

10101010

February 1999 3-41

LP2950/2951 Micrel

Typical Performance Characteristics (Continued)

Ripple Rejection

80

I = 50 µA

L

70
60

I = 100 mA

L

50
40

C = 1 µF

L

V = 6V

30

IN

V = 5V

OUT

20

RIPPLE REJECTION (dB)

10

123456

10 10 10101010

FREQUENCY (Hz)

Shutdown Threshold Voltage

1.8

1.6

1.4

1.2

1.0

0.8

0.6

-75 -50-25 0 25 50 75100125 150

SHUTDOWN THRESHOLD VOLTAGE (V)

TEMPERATURE (°C)

Output Noise LP2951 Divider Resistance

3.5

√

3.0

2.5
C = 220 µF

L

2.0

C =

1.5

1.0

VOLTAGE NOISE

0.5

SPECTRAL DENSITY (µV/ Hz)

0.0

L

3.3 µF

0.01 µF
BYPASS
PIN 1 TO
PIN 7

234 5

10 101010

I = 100 mA

L

C = 1 µF

L

Ω

400

300

200

100

0

PIN 2 TO PIN 4 RESISTANCE (k )

-75 -50-25 0 25 50 75100125 150

FREQUENCY (Hz) TEMPERATURE (°C)

LP2950 Maximum

Line Regulation

30
25

20
15
10

5

T = 150°C

J

I = 100 µA

L

I = 1 mA

L

0

10

5

T = 125°C

J

I = 100 µA

L

0

-5

-10

OUTPUT VOLTAGE CHANGE (mV)

5 1015202530

INPUT VOLTAGE (V) INPUT VOLTAGE (V)

Rated Output Current

120

100

80
60

T = 50°C

A

40
20

OUTPUT CURRENT (mA)

T = 85°C

A

0

0 5 10 15 20 25 30

8-PIN MOLDED
DIP SOLDERED
TO PC BOARD

T = 125°C

J

MAX

V = 5V

OUT

T = 25°C

A

LP2950 Maximum
Rated Output

120

TO-92 PACKAGE

T = 85°C

A

0.25" LEADS SOLDERED

100

80
60
40

20

OUTPUT CURRENT (mA)

0

0 5 10 15 20 3025

TO PC BOARD

T = 125°C

J

MAX

T = 25°C

A

Thermal Response

5
4
2

CHANGE (mV)

0

OUTPUT VOLTAGE

-2
1
0

POWER

-1

DISSIPATION (W)

01020 5030 40

1.25W

TIME (µs)INPUT VOLTAGE (V)

3-42 February 1999

LP2950/2951 Micrel

Applications Information

External Capacitors

A 1.0µF (or greater) capacitor is required between the LP2950/
LP2951 output and ground to prevent oscillations due to
instability. Most types of tantalum or aluminum electrolytics
will be adequate; film types will work, but are costly and
therefore not recommended. Many aluminum electrolytics
have electrolytes that freeze at about –30°C, so solid tantalum
capacitors are recommended for operation below –25°C. The
important parameters of the capacitor are an effective series
resistance of about 5Ω or less and a resonant frequency
above 500kHz. The value of this capacitor may be increased
without limit.

At lower values of output current, less output capacitance is
required for output stability. The capacitor can be reduced to

0.33µF for current below 10mA or 0.1µF for currents below
1mA. Using the 8-Pin 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.

The LP2950 will remain stable and in regulation with no load
in addition to the internal voltage divider, unlike many other
voltage regulators. 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 0.1µF 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 (pin 7)
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 remedy
this.

Error Detection Comparator Output

A logic low output will be produced by the comparator 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 1.235V reference voltage.
(Refer to the block diagram on Page 1). This trip level remains
“5% below normal” regardless of the programmed output
voltage of the LP2951. 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 is a timing diagram depicting the ERROR signal and
the regulated output voltage as the LP2951 input is ramped up
and down. The ERROR signal becomes valid (low) at about

1.3V input. It goes high at about 5V input (the input voltage at

which V

= 4.75V). Since the LP2951’s dropout voltage is

OUT

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
(approximately 4.75V) does not vary with load.

The error comparator has an open-collector output which
requires an external pull-up resistor. Depending on system
requirements, this resistor may be returned to the 5V output
or some other supply voltage. 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 1MΩ. The resistor is not
required if this output is unused.

Programming the Output Voltage (LP2951)

The LP2951 may be pin-strapped for 5V using its internal
voltage divider by tying Pin 1 (output) to Pin 2 (SENSE) and
Pin 7 (FEEDBACK) to Pin 6 (5V TAP). Alternatively, it may be
programmed for any output voltage between its 1.235V
reference and its 30V maximum rating. An external pair of
resistors is required, as shown in Figure 2.

The complete equation for the output voltage is
V
where V

OUT

= V

REF

x { 1 + R1/R2 } + IFB R

REF

2

is the nominal 1.235 reference voltage and IFB is
the feedback pin bias current, nominally 20 nA. The minimum
recommended load current of 1 µA forces an upper limit of 1.2
MΩ on the value of R2, if the regulator must work with no load
(a condition often found in CMOS in standby), IFB will produce
a 2% typical error in V

which may be eliminated at room

OUT

temperature by trimming R1. For better accuracy, choosing
R2 = 100kΩ reduces this error to 0.17% while increasing the
resistor program current to 12µA. 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 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 method by which noise can be
reduced on the 3 lead LP2950 and 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

C

BYPASS

≅

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 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.

1

π

2R

1

• 200 Hz

3

February 1999 3-43

LP2950/2951 Micrel

*SEE APPLICATIONS

V

7

OUT

1.23V

INFORMATION

V

OUT
x (1 + )

V

OUT

1.2

1

R

100

1

pF

R

2

30V

= V

R
R

3.3µF

REF

1
2

4.75V

OUTPUT

VOLTAGE

*

ERROR

INPUT

VOLTAGE

* SEE APPLICATIONS INFORMATION

NOT

VALID

1.3V

5V

*

NOT

VALID

+V

100kΩ

8
V

5

ERROR

ERROR

OUTPUT

LP2951

LP2951

OFF

3

SD

SHUTDOWN
INPUT

GND FB

ON

NOTE: PINS 2 AND 6 ARE LEFT OPEN

4

IN

IN

V

REF

Figure 1. ERROR Output Timing

Figure 2. Adjustable Regulator

Typical Applications

+V

IN

8

+V

IN

ERROR
OUTPUT

5

ERROR

V

OUT

*V ≈V

1

OUT

IN

LP2951

SHUTDOWN
INPUT

*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV,
DEPENDING ON LOAD CURRENT. CURRENT LIMIT IS TYPICALLY 160mA.

3

SO

GND

FB

4

7

Wide Input Voltage Range Current Limiter

*SLEEP
INPUT

47kΩ

OFF

5

3

ERROR

SD

ERROR
OUTPUT

SHUTDOWN
INPUT

ON

*HIGH INPUT LOWERS V

5 V Regulator with 2.5 V Sleep Function

+V

+V

LP2951

MIC2951

GND

4

TO 2.5V

OUT

IN

C-MOS
GATE

870 23

2N3906

100pF

470 kΩ

200kΩ
1%
100kΩ

1%
100kΩ

+V

+

OUT

3.3µF

8

IN

1

V

OUT

FB

7

3-44 February 1999

LP2950/2951 Micrel

V

+V

IN

+V

IN

V

OUT

LP2950Z

GND

5 Volt Current Limiter

*V = 5

OUT

+

1µF

SHUTDOWN
INPUT

+V = 2→30V

OUT

7

IL=

1.23
R

1

1µF

I

↓

L

LOAD

8

V

IN

V

LP2951

3

SD

GND

FB

4

R

1%

Low Drift Current Source

0.1µF

* MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV,
DEPENDING ON LOAD CURRENT.

Q1

2.7MΩ

3

SD

+V

+V

+V

IN

8

IN

LP2951

#1

GND

4

8

IN

LP2951

#2

GND

4

2

SENSE

V

OUT

ERROR

D

4

2

SENSE

V

OUT

ERROR

27kΩ

D

1

MEMORY

D

2

1µf

V+

20

3.6V
NICAD

RESET

µP

V

DO

D

1

5

EARLY WARNING

3

330kΩ

MAIN

OUTPUT

1

5

1µF

+

3

Regulator with Early Warning and Auxiliary Output

• 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

ITS ERROR FLAG BECOMES ACTIVE WHEN VIN ≤ 5.7 V. WHEN VIN DROPS
BELOW 5.3 V, THE ERROR FLAG OF REG. #2 BECOMES ACTIVE AND VIA Q1
LATCHES THE MAIN OUTPUT OFF. WHEN VIN AGAIN EXCEEDS 5.7 V REG. #1
IS BACK IN REGULATION AND THE EARLY WARNING SIGNAL RISES,
UNLATCHING REG. #2 VIA D3.

IS PROGRAMMED ONE DIODE DROP ABOVE 5 V.

OUT

February 1999 3-45

LP2950/2951 Micrel

+V

IN

20mA

4

8

470k

470k

RESET

5

3

ERROR

SD

+V

IN

LP2951

GND

4

V

OUT

FB

V

1

7

OUT

R

1

1N
4001

+

1µF

R

2

0.1µF

8

V

IN

MIC2951

GND

4

V

1

OUT

7

FB

1N457

MIN. VOLTAGE 4V

Latch Off When Error Flag Occurs Open Circuit Detector for 4mA to 20mA Current Loop

4.7mA

1

2

360

+5V

OUTPUT*

5

4

* HIGH FOR
I < 3.5mA

L

+

39kΩ

–

C4

+

6V
LEAD­ACID
BATTERY

C1-C4
LP339

RESET

1%

1%

1%

R

3

1%

39kΩ

100
kΩ

1
kΩ

1
kΩ

10kΩ

20kΩ

5

3

+V

IN

ERROR

SD

GND

–

C1

+

–

C2

+

–

C3

+

8

SENSE

LP2951

4

100kΩ

100kΩ

100kΩ

V

TAP

2

OUT

FB

6

<5.8V**

<6.0V**

<6.2V**

+V

1

OUT

+

= 5V

1µF

7

*OPTIONAL LATCH OFF WHEN DROP OUT OCCURS. ADJUST R3 FOR C2
SWITCHING WHEN V

**OUTPUTS GO LOW WHEN V

Regulator with State-of-Charge Indicator

3-46 February 1999

IS 6.0V

IN

DROPS BELOW DESIGNATED THRESHOLDS.

IN

LP2950/2951 Micrel

+

6V
SEALED
LEAD­ACID
BATTERY
SOURCE

≈ 400kΩ*

FOR 5.5V

* Sets disconnect voltage
** Sets disconnect hysteresis

For values shown, Regulator shuts down when VIN < 5.5 V and turns on again at 6.0 V. Current drain in disconnected mode is 150µA.

120kΩ

FB

1.5kΩ**

LM385

–

100kΩ

1N457

+V

LP2951

3

SD

GND

Low Battery Disconnect

+V

IN

8

IN

SENSE

4

V

OUT

1

2

+

1µF

MAIN V+

MEMORY V+

20Ω

+

NI-CAD
BACKUP
BATTERY

AUX. SHUTDOWN

INPUT

ON

TEMP.

SENSOR

LM34 for 125°F Shutdown
LM35 for 125°C Shutdown

OFF

+

LM34 OR

LM35

–

8

+V

IN

3

SD

GND

ERROR

MIC2951

4

V

FB

OUT

7

8.2kΩ

10kΩ

5° PRE-SHUTDOWN FLAG

5

1

EXTERNAL CIRCUIT

PROTECTED FROM

OVER TEMPERATURE

(V+ GOES OFF WHEN

TEMP.> 125°)

System Over Temperature Protection Circuit

3

OR

RELAY

February 1999 3-47

LP2950/2951 Micrel

50 kΩ

10 kΩ

Q42

Q40

R30

IN

Q15A

Q9

R11
18
kΩ

Q6

Q1

10

R1

20 kΩ

R2

50 kΩ

Q41

30
kΩ

R3

50 kΩ

R5

180

kΩ

ERROR

C1
pF

20

Q13

R4

13 kΩ

140

Q4Q3

R6
kΩ

Q12

Q38

Q39

Q5

Q2

31.4 kΩ

27.8 kΩ

Q37

R11

20.6
kΩ

R8

R9

R26
60 kΩ

Q7

Q11

Q36

R10

150

Q8

Q20

kΩ

R12

110

kΩ

Q34

R25

2.8 kΩ

Q18

Q16

R13
100

kΩ

GND

Q15B

R22
150 kΩ

Q17

C2
40 pF

R14
350
kΩ

FEEDBACK

R18
20kΩ

Q26

Q25

R17

Q14

12 kΩ

Q22

Q21

R15
100 kΩ

R16

R24
50 kΩ

30 kΩ

Q28

R23 60 kΩ

Q30

Q19

Q29

Q31

DENOTES CONNECTION ON LP2950 ONLY

R21 8 Ω

R17

10 Ω

Q23

SHDN

Q24

R27
182 kΩ

R28
60 kΩ

OUT

SENSE

5V TAP

3-48 February 1999