LP2950/2951
Micrel
LP2950/2951
100mA Low-Dropout Voltage Regulator
General Description
Features
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
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 Versions Only
•
•
•
Error flag warns of output dropout
Logic-controlled electronic shutdown
Output programmable from 1.24 to 29V
Block Diagram and Pin Configurations
UNREGULATED DC
7
+
8
FEEDBACK
INPUT
5V
150 mA
MAX.
1
OUTPUT
2
SENSE
+
3
FROM
CMOS
OR TTL
SHUTDOWN
–
182
kΩ
ERROR
AMPLIFIER
60 mV
+
1.23 V
REF.
+
5V TAP
60
kΩ
+
–
6
5
+
1.5 µF
TO CMOS
OR TTL
ERROR
ERROR
DETECTION
COMPARATOR
330
kΩ
4
GROUND
LP2950 and LP2951 Block Diagram
(Pin Numbers Refer to LP2951)
3 2
OUTPUT
1
8
SENSE
2
7
SHUTDOWN
3
6
4
5
OUTPUT
1
INPUT
GROUND
GROUND
INPUT
FEEDBACK
5V TAP
ERROR
DIP and SO Packages
(BN and BM)
TO-92 Plastic Package Bottom View
(BZ)
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
3
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
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.
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%
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
Input Supply Voltage
–40°C to +125°C
–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
Parameter
Condition
Output Voltage
TJ = 25°C
Output Voltage
–25°C ≤ TJ ≤ +85°C
Output Voltage
Over Full Temperature Range
Output Voltage
Over Load Variation
Output Voltage
Temperature Coefficient
Line Regulation
Load Regulation
Dropout Voltage
Ground Current
Dropout Current
February 1999
TA = 25°C except as noted.
Min
Typ
Max
Units
LP295x-02 (±0.5%)
4.975
5.000
5.025
V
LP295x-03 (±1%)
4.950
5.000
5.050
V
LP2951-4.8 (±1%)
4.802
4.850
4.899
V
LP295x-02 (±0.5%)
4.950
5.050
V
LP295x-03 (±1%)
4.925
5.075
V
LP2951-4.8 (±1%)
4.777
4.872
V
LP295x-02 (±0.5%), –40°C to +125°C
4.940
5.060
V
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
LP295x-02 (±0.5%), 100µA ≤ IL ≤ 100mA, TJ ≤ TJ(max)
4.930
5.070
V
LP295x-03 (±1%), 100µA ≤ IL ≤ 100mA, TJ ≤ TJ(max)
4.880
5.120
V
LP2951-4.8 (±1%), 100µA ≤ IL ≤ 100mA, TJ ≤ TJ(max)
4.733
4.967
V
LP295x-02 (±0.5%), Note 12
20
100
ppm/°C
LP295x-03 (±1%), Note 12
50
150
ppm/°C
LP2951-4.8 (±1%), Note 12
50
150
ppm/°C
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
%
%
LP295x-02 (±0.5%), Note 14, 100µA ≤ IL ≤ 100mA
0.04
0.10
0.20
%
%
LP295x-03 (±1%), Note 14, 100µA ≤ IL ≤ 100mA
0.10
0.20
0.30
%
%
LP2951-4.8 (±1%), Note 14, 100µA ≤ IL ≤ 100mA
0.10
0.20
0.30
%
%
Note 5, IL = 100µA
50
80
150
mV
mV
Note 5, IL = 100mA
380
450
600
mV
mV
IL = 100µA
100
150
200
µA
µA
IL = 100mA
8
12
14
mA
mA
180
250
310
µA
µA
VIN = 4.5V, IL = 100µA
3-37
3
LP2950/2951
Micrel
Parameter
Condition
Current Limit
Typ
Max
Units
VOUT = 0V
160
200
220
mA
mA
Thermal Regulation
Note 13
0.05
0.20
%/W
Output Noise
10Hz to 100kHz, CL = 1µF
430
µVRMS
10Hz to 100kHz, CL = 200µF
160
µVRMS
10Hz to 100kHz, CL = 3.3µF,
0.01µF bypass Feedback to Output
100
µVRMS
Reference Voltage
Reference Voltage
Min
LP295x-02 (±0.5%)
1.220
1.200
1.235
1.250
1.260
V
V
LP295x-03 (±1%)
1.210
1.200
1.235
1.260
1.270
V
V
LP2951-4.8 (±1%)
1.210
1.200
1.235
1.260
1.270
V
V
LP295x-02 (±0.5%), Note 7
1.190
1.270
V
LP295x-03 (±1%), Note 7
1.185
1.285
V
LP2951-4.8 (±1%), Note 7
1.185
1.285
V
40
60
nA
nA
Feedback Bias Current
Reference Voltage
20
LP295x-02 (±0.5%), Note 12
20
ppm/°C
LP295x-03 (±1%), Note 12
50
ppm/°C
LP2951-4.8 (±1%), Note 12
50
ppm/°C
0.1
nA/°C
Feedback Bias Current
Temperature Coefficient
Output Leakage Current
VOH = 30V
0.01
1.00
2.00
µA
µA
Output Low Voltage (Flag)
VIN = 4.5V, IOL = 200µA
150
250
400
mV
mV
Upper Threshold Voltage
Note 6
Lower Threshold Voltage
Note 6
75
Hysteresis
Note 6
15
Input Logic Voltage
LP295x-02 (±0.5%)
Low
High
1.3
40
25
60
mV
mV
95
140
mV
0.7
V
V
V
0.7
V
V
V
0.7
V
V
V
2.0
LP295x-03 (±1%)
Low
High
1.3
2.0
LP2951-4.8 (±1%)
Low
High
1.3
2.0
3-38
mV
mV
February 1999
LP2950/2951
Micrel
Parameter
Condition
Shutdown Input Current
Regulator Output Current
in Shutdown
Min
Typ
Max
Units
VSHUTDOWN = 2.4V
30
50
100
µA
µA
VSHUTDOWN = 30V
450
600
750
µA
µA
3
10
20
µA
µA
Note 11
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
are Feedback tied to 5V Tap and Output tied to Output Sense (VOUT = 5V) 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 100mV 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 6V input. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = VOUT /VREF =
(R1 + R2)/R2. For example, at a programmed output voltage of 5V, the Error output is guaranteed to go low when the output drops by
95mV x 5V/1.235V = 384mV. 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 – 1 V), 2.3V ≤ VIN ≤ 30V, 100µA < IL ≤ 100mA, TJ ≤ TJMAX.
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.
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.
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 diodeclamped to ground.
Note 11: VSHUTDOWN ≥ 2V, VIN ≤ 30 V, VOUT = 0, with Feedback pin tied to 5V Tap.
Note 12: Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
Note 13: Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load or line
regulation effects. Specifications are for a 50mA load pulse at VIN = 30V (1.25W pulse) for t = 10ms.
Note 14: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating
effects are covered in the specification for thermal regulation.
Note 15: Line regulation for the LP2951 is tested at 150°C for IL = 1mA. For IL = 100µA and TJ = 125°C, line regulation is guaranteed by design to
0.2%. See Typical Performance Characteristics for line regulation versus temperature and load current.
February 1999
3-39
3
LP2950/2951
Micrel
Quiescent Current
Dropout Characteristics
0.1
0.01
0.1
5
4
1
1
10
150
0
2 3 4
2
3
4
5
6
5
6 7
280
5.0
4.98
0.2%
4.96
GROUND CURRENT (µA)
5.04
5.02
VIN = 6V
IL = 100 mA
8
TEMPERATURE (°C)
Short Circuit Current
110
100
-75 -50 -25 0 25 50 75 100 125 150
TEMPERATURE (°C)
1
2
3
4
5
6
7
8
Ground Current
14
12
IL = 100 mA
10
8
6
4
2
0
0
1
2
3
4
5
6
7
8
INPUT VOLTAGE (V)
Drop-out Voltage
DROP-OUT VOLTAGE (mV)
120
40
INPUT VOLTAGE (VOLTS)
Drop-out Voltage
500
600
170
130
80
0
GROUND CURRENT (mA)
GROUND CURRENT (mA)
12
TEMPERATURE (°C)
140
IL = 0
120
16
-75 -50 -25 0 25 50 75 100 125 150
150
160
Ground Current
4
-75 -50 -25 0 25 50 75 100 125 150
160
IL = 1 mA
200
0
16
180
240
TEMPERATURE (°C)
Quiescent Current
5 6 7 8 9 10
Ground Current
320
4.94
-75 -50 -25 0 25 50 75 100 125 150
240
200
0 1 2 3 4
INPUT VOLTAGE (VOLTS)
5.06
INPUT VOLTAGE (VOLTS)
VIN = 6V
IL = 100 µA
RL = ∞
INPUT VOLTAGE (VOLTS)
8 9 10
220
R L = 50k Ω
150
125
100
75
50
Output Voltage vs.
Temperature of 3
Representative Units
R L = 50 Ω
0 1
1
250
225
200
175
25
0
0
OUTPUT VOLTAGE (V)
INPUT CURRENT (mA)
R L = 50 Ω
2
Input Current
QUIESCENT CURRENT (µA)
R L = 50kΩ
3
LOAD CURRENT (mA)
SHORT CIRCUIT CURRENT (mA)
INPUT CURRENT (µA)
1
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Input Current
6
IL = 100 mA
500
400
300
100
50
IL = 100 µA
0
-75 -50 -25 0 25 50 75 100 125 150
TEMPERATURE (°C)
3-40
DROP-OUT VOLTAGE (mV)
10
OUTPUT VOLTAGE (VOLTS)
GROUND PIN CURRENT (mA)
Typical Performance Characteristics
400
300
200
TJ = 25 °C
100
0
100 µA
1 mA
10 mA
100 mA
OUTPUT CURRENT
February 1999
Micrel
LP2951
Minimum Operating Voltage
2.0
1.9
1.8
1.7
1.6
-75 -50 -25 0 25 50 75 100 125 150
10
0
-10
-20
-30
-75 -50 -25 0 25 50 75 100 125 150
TEMPERATURE (°C)
4
HYSTERESIS
2
0
PULLUP RESISTOR TO
SEPARATE 5V SUPPLY
1
2
3
4
1.5
1.0
TA = -55°C
0.5
1
2
3
4
5
OUTPUT VOLTAGE
CHANGE (mV)
0
80
60
40
20
0
-20
-40
-60
LOAD
CURRENT
100
mA
100
µA
TA = 25°C
0.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
5
C L = 1 µF
VOUT = 5V
TA = 125°C
2.0
Load Transient Response
250
200
150
100
50
0
-50
-100
100
mA
100
µA
I0 = 100 mA
0.5
VOUT = 5V
C L = 1 µF
0.05
0.02
0.01
10
100
1K
10K 100K 1M
FREQUENCY (Hz)
February 1999
TA = 25°C
-200
TA = –55°C
-250
-2.0 -1.5 -1.0 -0.5 0
C L = 10 µF
VOUT = 5V
12
16
20
8V
6V
4V
7
6
5
4
3
2
1
0
200
2
0
-2
800
IL = 10 mA
VIN = 8V
CL = 10 µF VOUT = 5V
-100 0 100 200 300 400 500 600 700
Ripple Rejection
90
70
IL = 0
60
50
20
600
TIME (µs)
80
30
400
L L = 1 µF
Ripple Rejection
40
3
C L = 1 µF
IL = 1 mA
VOUT = 5V
LP2951
Enable Transient
8
1.0
0
-50
mV
Load Transient Response
4
0.5
Line Transient Response
100
mV
50
mV
TIME (ms)
RIPPLE REJECTION (dB)
OUTPUT IMPEDANCE (OHMS)
I0 = 1 mA
0.2
0.1
-150
0
90
I0 = 100 µA
2
1
TA = 125°C
-100
TIME (µs)
0
Output Impedance
5
-50
OUTPUT LOW VOLTAGE (V)
TIME (ms)
10
OUTPUT VOLTAGE
CHANGE
VOUT = 5V
INPUT VOLTAGE (V)
OUTPUT VOLTAGE
LOAD
CHANGE (mV)
CURRENT
LP2951
Comparator Sink Current
INPUT
VOLTAGE
2.5
6
0
PIN 7 DRIVEN BY EXTERNAL
SOURCE (REGULATOR RUN
OPEN LOOP)
0
FEEDBACK VOLTAGE (V)
SHUTDOWN
OUTPUT
PIN VOLTAGE (V) VOLTAGE (V)
LP2951
Error Comparator Output
-2
LP2951
Feedback Pin Current
TEMPERATURE (°C)
SINK CURRENT (mA)
COMPARATOR OUTPUT (V)
8
50
FEEDBACK CURRENT (µA)
2.1
LP2951
Feedback Bias Current
20
RIPPLE REJECTION (dB)
2.2
BIAS CURRENT (nA)
MINIMUM OPERATING VOLTAGE (V)
LP2950/2951
CL = 1 µF
VIN = 6V
VOUT = 5V
101
10 2
IL = 100 µA
10 3
10 4
10
FREQUENCY (Hz)
3-41
106
80
CL = 1 µF
VIN = 6V
VOUT = 5V
70 I = 1 mA
L
60
50
40
30
20
101
IL = 10 mA
102
10 3
10 4
10 5
FREQUENCY (Hz)
106
LP2950/2951
Micrel
Typical Performance Characteristics (Continued)
40
CL = 1 µF
30 VIN = 6V
VOUT = 5V
20
101
102
10 3
10 4
10 5
Output Noise
IL = 100 mA
3.0
2.5
CL = 1 µF
CL = 220 µF
2.0
CL =
3.3 µF
1.5
1.0
0.01 µF
BYPASS
PIN 1 TO
PIN 7
0.5
0.0
102
106
10 3
10 4
10 5
LP2951 Divider Resistance
400
300
200
100
0
-75 -50 -25 0 25 50 75 100 125 150
FREQUENCY (Hz)
1.6
1.4
1.2
1.0
0.8
0.6
-75 -50 -25 0 25 50 75 100 125 150
30
25
20
15
T = 150°C
10 J
5
0
120
IL = 1 mA
IL = 100 µA
8-PIN MOLDED
DIP SOLDERED
TO PC BOARD
100
TJ
TO-92 PACKAGE
0.25" LEADS SOLDERED
TO PC BOARD
100
80
TJ
60
MAX
= 125°C
TA = 25°C
40
TA = 85°C
0
5
10
15
20
25
30
MAX
= 125°C
VOUT = 5V
80
TA = 25°C
60
TA = 50°C
40
TA = 85°C
20
0
20
25
30
0
5
10 15 20 25
INPUT VOLTAGE (V)
40
50
INPUT VOLTAGE (V)
LP2950 Maximum
Rated Output
0
LP2950 Maximum
Rated Output Current
IL = 100 µA
10
5 TJ = 125°C
0
-5
-10
5
10
15
TEMPERATURE (°C)
20
TEMPERATURE (°C)
Line Regulation
OUTPUT VOLTAGE CHANGE (mV)
Shutdown Threshold Voltage
1.8
OUTPUT CURRENT (mA)
SHUTDOWN THRESHOLD VOLTAGE (V)
FREQUENCY (Hz)
120
PIN 2 TO PIN 4 RESISTANCE (kΩ )
IL = 100 mA
50
10
3.5
OUTPUT CURRENT (mA)
60
IL = 50 µA
POWER
OUTPUT VOLTAGE
DISSIPATION (W) CHANGE (mV)
70
Ripple Rejection
VOLTAGE NOISE
SPECTRAL DENSITY (µV/√Hz)
RIPPLE REJECTION (dB)
80
INPUT VOLTAGE (V)
30
Thermal Response
5
4
2
0
-2
1
1.25W
0
-1
0
10
20
30
TIME (µs)
3-42
February 1999
LP2950/2951
Micrel
Applications Information
External Capacitors
which VOUT = 4.75V). Since the LP2951’s dropout voltage is
load-dependent (see curve in Typical Performance
Characteristics), the input voltage trip point (about 5V) will
vary with the load current. The output voltage trip point
(approximately 4.75V) does not vary with load.
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.
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.
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 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 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
February 1999
Programming the Output Voltage (LP2951)
The complete equation for the output voltage is
VOUT = VREF x { 1 + R1/R2 } + IFB R2
where VREF 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 VOUT which may be eliminated at room
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
1
CBYPASS ≅
2 π R1 • 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 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.
3-43
3
LP2950/2951
Micrel
4.75V
OUTPUT
VOLTAGE
100kΩ
NOT
VALID
NOT
VALID
VOUT = V REF
R1
x (1 +
)
R2
VOUT
1.2 30V
8
VIN
5 ERROR
ERROR
OUTPUT
*
*
ERROR
*SEE APPLICATIONS
INFORMATION
+VIN
VOUT 1
LP2951
LP2951
SHUTDOWN 3
SD
INPUT
3.3µF
R1 100
pF
OFF
INPUT
VOLTAGE
5V
1.3V
GND
4
ON
FB
7
1.23V
NOTE: PINS 2 AND 6 ARE LEFT OPEN
* SEE APPLICATIONS INFORMATION
R2
V REF
Figure 1. ERROR Output Timing
Figure 2. Adjustable Regulator
Typical Applications
+V IN
+VIN
8
+VIN
ERROR
OUTPUT
5 ERROR
4
870 23
47kΩ
*VOUT ≈VIN
VOUT 1
470 kΩ
8
+V IN
LP2951
SHUTDOWN 3
SO
INPUT
GND
C-MOS
GATE
*SLEEP
INPUT
ERROR
OUTPUT
5
ERROR
V OUT 1
LP2951
MIC2951
SHUTDOWN 3
SD
INPUT
OFF
GND
ON
4
FB
7
FB
+V OUT
200kΩ
+
2N3906 1%
100kΩ
100pF
3.3µF
7
1%
100kΩ
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV,
DEPENDING ON LOAD CURRENT. CURRENT LIMIT IS TYPICALLY 160mA.
*HIGH INPUT LOWERS VOUT TO 2.5V
5 V Regulator with 2.5 V Sleep Function
Wide Input Voltage Range Current Limiter
3-44
February 1999
LP2950/2951
Micrel
+V IN
+V = 2 → 30V
IL↓
I L=
LOAD
1.23
+V IN
R
*V
VOUT
8
VIN
OUT
= 5V
LP2950Z
VOUT
1
+
1µF
LP2951
SHUTDOWN 3
SD
INPUT
GND
GND
0.1µF
FB
7
4
R
1%
5 Volt Current Limiter
* MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV,
DEPENDING ON LOAD CURRENT.
1µF
Low Drift Current Source
+V IN
3
D1
8
+V IN
2
SENSE
VOUT
D2
1
MEMORY
V+
20
LP2951
#1
5
ERROR
1µF
3.6V
NICAD
GND
4
27kΩ
D3
D4
2.7MΩ
RESET
Q1
8
+V IN
2
SENSE
VOUT
3
EARLY WARNING
SD
1
LP2951
#2
5
ERROR
330kΩ
MAIN
OUTPUT
+
µP
VDO
1µf
GND
4
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 VOUT IS PROGRAMMED ONE DIODE DROP ABOVE 5 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.
February 1999
3-45
LP2950/2951
Micrel
+V IN
4
+5V
4.7mA
20mA
8
470k
8
+V IN
5
470k
VOUT
ERROR
RESET
7
1µF
1
4
7
0.1µF
2
FB
R2
GND
GND
4
4
360
8
+VIN
5
2
SENSE
VOUT 1
ERROR
RESET
LP2951
–
3
C4
+
39kΩ
6V
1%
LEADACID
BATTERY
1%
100
kΩ
FB
SD
GND
4
1%
1
kΩ
C1
<5.8V**
100kΩ
–
C2
<6.0V**
100kΩ
–
C3
+
R3
1%
7
100kΩ
–
+
1
kΩ
+VOUT = 5V
+
1µF
TAP
6
+
C1-C4
LP339
4V
Open Circuit Detector for 4mA to 20mA Current Loop
39kΩ
+
* HIGH FOR
IL < 3.5mA
1N457
MIN. VOLTAGE
Latch Off When Error Flag Occurs
OUTPUT*
5
MIC2951
+
FB
SD
V OUT
1N
4001
R1
LP2951
3
VOUT
1
1
V IN
<6.2V**
10kΩ
20kΩ
*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.
Regulator with State-of-Charge Indicator
3-46
February 1999
LP2950/2951
Micrel
+
6V
120kΩ
1.5kΩ** 1N457
SEALED
LEADACID
BATTERY FB
LM385
SOURCE
–
≈ 400kΩ*
FOR 5.5V
3
100kΩ
8
+V IN
VOUT 1
MAIN V+
LP2951
SENSE
SD
2
MEMORY V+
1µF
GND
4
+
20Ω
+
* Sets disconnect voltage
** Sets disconnect hysteresis
NI-CAD
BACKUP
BATTERY
Low Battery Disconnect
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.
+VIN
8
+VIN
3
AUX. SHUTDOWN
INPUT
ERROR
SD
5
5° PRE-SHUTDOWN FLAG
3
MIC2951
OFF
VOUT 1
ON
+
TEMP. LM34 OR
SENSOR
LM35
–
LM34 for 125°F Shutdown
LM35 for 125°C Shutdown
February 1999
10kΩ
GND
4
EXTERNAL CIRCUIT
PROTECTED FROM
OVER TEMPERATURE
(V+ GOES OFF WHEN
TEMP.> 125°)
FB
7
8.2kΩ
System Over Temperature Protection Circuit
3-47
OR
RELAY
LP2950/2951
Micrel
FEEDBACK
IN
R18
20kΩ
Q15A
Q15B
Q24
Q26
Q25
OUT
Q9
Q3
R11
18
kΩ
Q4
Q7
C1
20
pF
Q6
R11
20.6
kΩ
Q1
10
R2
50 kΩ
Q17
Q16
R27
182 kΩ
R17
12 kΩ
Q14
5V TAP
R28
60 kΩ
Q2
Q20
R1
20 kΩ
Q42
SENSE
Q8
Q5
R5
180
kΩ
Q40
R6
140
kΩ
Q13
Q22
R10
150
kΩ
R8
31.4 kΩ
Q21
R9
27.8 kΩ
R12
110
kΩ
Q12
Q41
Q23
C2
40 pF
R13
100
kΩ
R15
100 kΩ
R14
350
kΩ
R16
30 kΩ
Q11
R17
10 Ω
Q29
R30
30
kΩ
Q18
Q19
Q28
R3
50 kΩ
R4
13 kΩ
R21 8 Ω
50 kΩ
Q30 Q31
Q37
10 kΩ
R22
150 kΩ
Q36
SHDN
R24
50 kΩ
R23 60 kΩ
ERROR
Q38
Q34
R26
60 kΩ
DENOTES CONNECTION ON LP2950 ONLY
R25
2.8 kΩ
GND
Q39
3-48
February 1999