LP2951
100 mA Low-Dropout Voltage Regulator
Features
General Description
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The LP2951 is micropower voltage regulators with very
low dropout voltage (typically 40 mV at light loads and
380 mV at 100 mA), and very low quiescent current
(75 μA typical). The quiescent current of the LP2951
increases only slightly in dropout, thus prolonging
battery life. This feature, among others, makes the
LP2951 ideally suited for use in battery-powered
systems.
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 1 μF for Stability
Current and Thermal Limiting
Error Flag Warns of Output Dropout
Logic-Controlled Electronic Shutdown
Output Programmable from 1.24V to 29V
Applications
• Automotive Electronics
• Voltage Reference
• Avionics
Available system functions, such as programmable
output voltage and logic-controlled shutdown, are
available as well.
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 LP2951 is available as either a -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 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.
Package Types
LP2951
DIP & SOIC
Top View
1
8
SENSE
2
7
SHUTDOWN
3
6
4
5
OUTPUT
GROUND
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.
2017 - 2022 Microchip Technology Inc. and its subsidiaries
DS20005736B-page 1
LP2951
Functional Block Diagram
5V
150 mA
MAX.
UNREGULATED DC
7
+
8
FEEDBACK
INPUT
1
OUTPUT
2
SENSE
+
3
FROM
CMOS
OR TTL
–
SHUTDOWN
182
kΩ
60 mV
1.23 V
REF.
–
+
5V TAP
60
kΩ
+
+
6
ERROR
AMPLIFIER
+
5
330
kΩ
1.5 μF
TO CMOS
OR TTL
ERROR
ERROR
DETECTION
COMPARATOR
4
GROUND
Typical Application Diagrams
+V IN
+VIN
8
+VIN
ERROR
OUTPUT
5
VOUT
ERROR
1 *VOUT ≈ VIN
LP2951
FB
4
7
5
470 kΩ
8
+V IN
ERROR
WIDE INPUT VOLTAGE RANGE
CURRENT LIMITER
+V OUT
V OUT 1
LP2951
MIC2951
SHUTDOWN 3
SD
INPUT
OFF
FB
GND
ON
7
4
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40 mV TO 400 mV,
DEPENDING ON LOAD CURRENT. CURRENT LIMIT IS TYPICALLY 160 mA.
IL
47kΩ
ERROR
OUTPUT
SHUTDOWN 3
SO
INPUT
GND
+V = 2
C-MOS
GATE
*SLEEP
INPUT
200kΩ
+
2N3906 1%
100kΩ
100pF
3.3μF
1%
100kΩ
*HIGH INPUT LOWERS VOUT TO 2.5V
5V REGULATOR WITH 2.5V
SLEEP FUNCTION
30V
I L=
LOAD
1.23
R
8
VIN
VOUT 1
LP2951
SHUTDOWN 3
SD
INPUT
GND
FB
4
0.1μF
7
R
1%
1μF
LOW DRIFT CURRENT SOURCE
DS20005736B-page 2
2017 - 2022 Microchip Technology Inc. and its subsidiaries
LP2951
Typical Application Diagrams
+V IN
D1
+V IN
2
SENSE
8
+V IN
VOUT
D2
1
MEMORY
V+
8
470k
20
LP2951
#1
5
ERROR
1μF
3.6V
NICAD
+V IN
5
470k
GND
4
Q1
RESET
2
SENSE
SD
VOUT
LP2951
#2
5
ERROR
330kΩ
MAIN
OUTPUT
+
7
+
FB
SD
1μF
R2
GND
RESET
8
+V IN
1
3
3
EARLY WARNING
D3
D4
2.7MΩ
R1
LP2951
27kΩ
VOUT
VOUT 1
ERROR
4
μP
VDO
LATCH-OFF WHEN ERROR FLAG OCCURS
1μf
GND
4
• 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 5V.
ITS ERROR FLAG BECOMES ACTIVE WHEN VIN ≤ 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 VIN AGAIN EXCEEDS 5.7V REG. #1
IS BACK IN REGULATION AND THE EARLY WARNING SIGNAL RISES,
UNLATCHING REG. #2 VIA D3.
REGULATOR WITH EARLY WARNING
AND AUXILIARY OUTPUT
4
+5V
4.7mA
20mA
8
+VIN
39kΩ
8
1
V IN
1N
4001
V OUT
VOUT 1
ERROR
RESET
LP2951
–
3
C4
+
4
7
2
FB
GND
4
5
1
LP2951
0.1μF
OUTPUT*
5
2
SENSE
360
39kΩ
* HIGH FOR
IL < 3.5mA
FB
SD
GND
4
+VOUT = 5V
+
1μF
7
TAP
6
1N457
+
MIN. VOLTAGE
4V
OPEN CIRCUIT DETECTOR FOR 4 mA
TO 20 mA CURRENT LOOP
6V
1%
LEADACID
BATTERY
1%
100
kΩ
–
100kΩ
C1
+
1
kΩ
–
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