LP2951CMMX-3.3 [NSC]
Series of Adjustable Micropower Voltage Regulators; 系列微功率可调稳压器
| 型号： | LP2951CMMX-3.3 |
| 厂家： | 
National Semiconductor |
| 描述： | Series of Adjustable Micropower Voltage Regulators |
| 文件： | 总26页 (文件大小：1200K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
May 2005
LP2950/LP2951
Series of Adjustable Micropower Voltage Regulators
(.05% typ.) and a very low output voltage temperature coef-
ficient, making the part useful as a low-power voltage refer-
ence.
General Description
The LP2950 and LP2951 are micropower voltage regulators
with very low quiescent current (75µA typ.) and very low
dropout voltage (typ. 40mV at light loads and 380mV at
100mA). They are ideally suited for use in battery-powered
systems. Furthermore, the quiescent current of the LP2950/
LP2951 increases only slightly in dropout, prolonging battery
life.
Features
n 5V, 3V, and 3.3V versions available
n High accuracy output voltage
n Guaranteed 100mA output current
n Extremely low quiescent current
n Low dropout voltage
n Extremely tight load and line regulation
n Very low temperature coefficient
n Use as Regulator or Reference
n Needs minimum capacitance for stability
n Current and Thermal Limiting
n Stable with low-ESR output capacitors (10mΩ to 6Ω)
The LP2950-5.0 is available in the surface-mount D-Pak
package, and in the popular 3-pin TO-92 package for pin-
compatibility with older 5V regulators. The 8-lead LP2951 is
available in plastic, ceramic dual-in-line, LLP, or metal can
packages and offers additional system functions.
One such feature is an error flag output which warns of a low
output voltage, often due to falling batteries on the input. It
may be used for a power-on reset. A second feature is the
logic-compatible shutdown input which enables the regulator
to be switched on and off. Also, the part may be pin-strapped
for a 5V, 3V, or 3.3V output (depending on the version), or
programmed from 1.24V to 29V with an external pair of
resistors.
LP2951 versions only
n Error flag warns of output dropout
n Logic-controlled electronic shutdown
n Output programmable from 1.24 to 29V
Careful design of the LP2950/LP2951 has minimized all
contributions to the error budget. This includes a tight initial
tolerance (.5% typ.), extremely good load and line regulation
Block Diagram and Typical Applications
LP2950
LP2951
00854625
00854601
© 2005 National Semiconductor Corporation
DS008546
www.national.com
Connection Diagrams
TO-252 (D-Pak)
TO-92 Plastic Package (Z)
00854602
Bottom View
00854670
Front View
8-Lead LLP
Dual-In-Line Packages (N, J)
Surface-Mount Package (M, MM)
00854626
Top View
Metal Can Package (H)
00854671
Pin 4 is fused to center DAP
Top View
00854619
Top View
10-Lead Ceramic Surface-Mount Package (WG)
00854664
Top View
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2
Ordering Information
Package
Temperature
Range
Part Number
Package Marking
Transport Media
NSC Drawing
<
<
TO-92 (Z) −40 TJ 125
LP2950ACZ-3.0
LP2950CZ-3.0
LP2950ACZ-3.3
LP2950CZ-3.3
LP2950ACZ-5.0
LP2950CZ-5.0
LP2950CDT-3.0
LP2950CDTX-3.0
LP2950CDT-3.3
LP2950CDTX-3.3
LP2950CDT-5.0
LP2950CDTX-5.0
LP2951ACN-3.0
LP2951CN-3.0
LP2951ACN-3.3
LP2951CN-3.3
LP2951ACN
2950A CZ3.0
2950 CZ3.0
Bag
Z03A
Bag
2950A CZ3.3
2950 CZ3.3
Bag
Bag
2950A CZ5.0
2950 CZ5.0
Bag
Bag
<
<
TO-252
(D-Pak)
−40 TJ 125
LP2950CDT-3.0
75 Units/Rail
TD03B
N08E
M08A
2.5k Units Tape and Reel
75 Units/Rail
LP2950CDT-3.3
LP2950CDT-5.0
2.5k Units Tape and Reel
75 Units/Rail
2.5k Units Tape and Reel
40 Units/Rail
<
<
N (N-08E) −40 TJ 125
LP2951ACN-3.0
LP2951CN-3.0
LP2951ACN-3.3
LP2951CN-3.3
LP2951ACN
40 Units/Rail
40 Units/Rail
40 Units/Rail
40 Units/Rail
LP2951CN
LP2951CN
40 Units/Rail
<
<
M (M08A) −40 TJ 125
LP2951ACM-3.0
LP2951ACMX-3.0
LP2951CM-3.0
LP2951CMX-3.0
LP2951ACM-3.3
LP2951ACMX-3.3
LP2951CM-3.3
LP2951CMX-3.3
LP2951ACM
2951ACM30*
95 Units/Rail
(where * is die rev letter)
2.5k Units Tape and Reel
95 Units/Rail
2951CM30*
(where * is die rev letter)
2.5k Units Tape and Reel
95 Units/Rail
2951ACM33*
(where * is die rev letter)
2.5k Units Tape and Reel
95 Units/Rail
2951CM33*
(where * is die rev letter)
2.5k Units Tape and Reel
95 Units/Rail
2951ACM*
(where * is die rev letter)
LP2951ACMX
2.5k Units Tape and Reel
95 Units/Rail
LP2951CM
2951CM*
(where * is die rev letter)
LP2951CMX
2.5k Units Tape and Reel
1k Units Tape and Reel
3.5k Units Tape and Reel
1k Units Tape and Reel
3.5k Units Tape and Reel
1k Units Tape and Reel
3.5k Units Tape and Reel
1k Units Tape and Reel
3.5k Units Tape and Reel
1k Units Tape and Reel
3.5k Units Tape and Reel
1k Units Tape and Reel
3.5k Units Tape and Reel
40 Units/Rail
<
<
MM
−40 TJ 125
LP2951ACMM-3.0
LP2951ACMMX-3.0
LP2951CMM-3.0
LP2951CMMX-3.0
LP2951ACMM-3.3
LP2951ACMMX-3.3
LP2951CMM-3.3
LP2951CMMX-3.3
LP2951ACMM
LP2951ACMMX
LP2951CMM
L0BA
L0BB
L0CA
L0CB
L0DA
L0DB
MUA08A
(MUA08A)
LP2951CMMX
LP2951J/883
<
<
<
<
J (J08A)
H (H08C)
WG
−55 TJ 150
See MIL/AERO Datasheet
See MIL/AERO Datasheet
See MIL/AERO Datasheet
J08A
H08C
<
−55 TJ 150
LP2951H/883
Tray
<
−55 TJ 150
LP2951WG/883
Tray
WG10A
(WG10A)
3
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Ordering Information (Continued)
Package
Temperature
Range
Part Number
Package Marking
51AC30
Transport Media
NSC Drawing
<
<
8-lead
LLP
−40 TJ 125
LP2951ACSD-3.0
LP2951ACSDX-3.0
LP2951CSD-3.0
LP2951CSDX-3.0
LP2951ACSD-3.3
LP2951ACSDX-3.3
LP2951CSD-3.3
LP2951CSDX-3.3
LP2951ACSD
1k Units Tape and Reel
4.5k Units Tape and Reel
1k Units Tape and Reel
4.5k Units Tape and Reel
1k Units Tape and Reel
4.5k Units Tape and Reel
1k Units Tape and Reel
4.5k Units Tape and Reel
1k Units Tape and Reel
4.5k Units Tape and Reel
1k Units Tape and Reel
4.5k Units Tape and Reel
SDC08A
51AC30B
51AC33
51AC33B
2951AC
LP2951ACSDX
LP2951CSD
2951ACB
LP2951CSDX
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4
Absolute Maximum Ratings (Note 1)
ESD Rating
Human Body Model(Note 18)
2500V
30V
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Operating Ratings (Note 1)
Maximum Input Supply Voltage
Junction Temperature Range
(TJ) (Note 8)
Input Supply Voltage
SHUTDOWN Input Voltage,
Error Comparator Output
Voltage, (Note 9)
−0.3 to +30V
LP2951
−55˚ to +150˚C
−40˚ to +125˚C
FEEDBACK Input Voltage
(Note 9) (Note 10)
−1.5 to +30V
LP2950AC-XX, LP2950C-XX,
LP2951AC-XX, LP2951C-XX
Power Dissipation
Internally Limited
+150˚C
Junction Temperature (TJ)
Ambient Storage Temperature
Soldering Dwell Time, Temperature
Wave
−65˚ to +150˚C
4 seconds, 260˚C
10 seconds, 240˚C
75 seconds, 219˚C
Infrared
Vapor Phase
Electrical Characteristics (Note 2)
LP2951
LP2950AC-XX
LP2951AC-XX
Tested Design
LP2950C-XX
LP2951C-XX
Tested Design
Limit Limit
Conditions
(Note 2)
Parameter
Tested
Limit
Units
Typ
Typ
Limit
Limit
Typ
(Notes 3, 16)
(Note 3) (Note 4)
(Note 3) (Note 4)
3V Versions (Note 17)
Output Voltage
TJ = 25˚C
3.0
3.0
3.0
3.015
2.985
3.0
3.0
3.0
3.015
2.985
3.030
2.970
3.036
2.964
3.0
3.0
3.0
3.030
2.970
3.045
2.955
3.060
2.940
V max
V min
V max
V min
V max
V min
−25˚C ≤ TJ ≤ 85˚C
Full Operating
Temperature
Range
3.036
2.964
Output Voltage
100µA ≤ IL
100mA
≤
3.045
2.955
3.042
2.958
3.072
2.928
V max
V min
3.0
3.0
3.0
TJ ≤ TJMAX
3.3V Versions (Note 17)
Output Voltage TJ = 25˚C
3.3
3.3
3.3
3.317
3.284
3.3
3.3
3.3
3.317
3.284
3.333
3.267
3.340
3.260
3.3
3.3
3.3
3.333
3.267
3.350
3.251
3.366
3.234
V max
V min
V max
V min
V max
V min
−25˚C ≤ TJ ≤ 85˚C
Full Operating
Temperature
Range
3.340
3.260
Output Voltage
100µA ≤ IL
100mA
≤
3.350
3.251
3.346
3.254
3.379
3.221
V max
V min
3.3
3.3
3.3
TJ ≤ TJMAX
5V Versions (Note 17)
Output Voltage
TJ = 25˚C
5.0
5.0
5.0
5.025
4.975
5.0
5.0
5.0
5.025
4.975
5.05
5.0
5.0
5.0
5.05
4.95
5.075
4.925
5.1
V max
V min
V max
V min
V max
−25˚C ≤ TJ ≤ 85˚C
4.95
Full Operating
5.06
5.06
5
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Electrical Characteristics (Note 2) (Continued)
LP2951
LP2950AC-XX
LP2951AC-XX
Tested Design
LP2950C-XX
LP2951C-XX
Conditions
(Note 2)
Parameter
Tested
Limit
Tested Design
Units
Typ
Typ
Limit
Limit
Typ
Limit
Limit
(Notes 3, 16)
4.94
(Note 3) (Note 4)
(Note 3) (Note 4)
Temperature
Range
4.94
4.9
V min
V max
V min
Output Voltage
100µA ≤ IL
100mA
≤
5.075
4.925
120
5.075
4.925
100
5.12
4.88
150
5.0
5.0
5.0
TJ ≤ TJMAX
All Voltage Options
Output Voltage
Temperature
Coefficient
(Note 12)
20
20
50
0.04
0.1
ppm/˚C
Line Regulation
(Note 14)
(VONOM + 1)V ≤
Vin ≤ 30V (Note
15)
0.03
0.04
0.1
0.03
0.04
0.1
0.2
% max
% max
0.5
0.2
0.4
Load Regulation
(Note 14)
100µA ≤ IL
≤
0.1
0.3
80
0.1
0.2
80
0.2
0.3
80
% max
% max
100mA
Dropout Voltage
(Note 5)
IL = 100µA
IL = 100mA
IL = 100µA
IL = 100mA
mV max
mV max
mV max
mV max
µA max
µA max
mA max
mA max
µA max
50
150
450
600
120
140
12
50
150
450
600
120
140
12
50
150
450
600
120
140
12
380
75
380
75
380
75
Ground
Current
8
8
8
14
14
14
Dropout
Vin = (VONOM −
0.5)V
110
170
110
170
110
170
Ground Current
Current Limit
IL = 100µA
Vout = 0
200
200
220
0.2
200
200
µA max
mA max
mA max
%/W
160
0.05
430
160
100
160
0.05
430
160
100
200
220
0.2
160
0.05
430
160
100
200
220
0.2
Thermal Regulation
Output Noise,
(Note 13)
max
CL = 1µF (5V
Only)
µV rms
10 Hz to 100 kHz
CL = 200µF
CL = 3.3µF
(Bypass = 0.01µF
Pins 7 to 1
(LP2951)
µV rms
µV rms
8-pin Versions Only
Reference
LP2951
1.25
1.26
1.22
1.2
LP2951AC-XX
LP2951C-XX
1.26
1.235
1.235
1.25
1.26
1.22
1.2
1.235
V max
V max
V min
Voltage
1.27
1.21
1.2
V min
Reference
(Note 7)
1.27
1.19
40
1.27
1.19
40
1.285
1.185
40
V max
V min
Voltage
Feedback Pin
Bias Current
Reference Voltage
20
20
20
20
20
50
nA max
nA max
ppm/˚C
60
60
60
(Note 12)
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6
Electrical Characteristics (Note 2) (Continued)
LP2951
LP2950AC-XX
LP2951AC-XX
Tested Design
LP2950C-XX
LP2951C-XX
Conditions
(Note 2)
Parameter
Tested
Limit
Tested Design
Units
Typ
Typ
Limit
Limit
Typ
Limit
Limit
(Notes 3, 16)
(Note 3) (Note 4)
(Note 3) (Note 4)
All Voltage Options
Temperature
Coefficient
Feedback Pin Bias
Current Temperature
Coefficient
0.1
0.1
0.1
nA/˚C
Error Comparator
Output Leakage
Current
VOH = 30V
0.01
150
1
2
0.01
150
1
0.01
150
1
µA max
µA max
mV max
2
2
Output Low
Vin = (VONOM −
0.5)V
250
250
250
Voltage
IOL = 400µA
(Note 6)
400
40
400
400
mV max
mV min
mV min
mV max
mV max
mV
Upper Threshold
Voltage
60
75
15
1.3
60
75
15
1.3
40
60
75
15
1.3
40
25
25
25
Lower Threshold
Voltage
(Note 6)
(Note 6)
95
95
95
140
140
140
Hysteresis
Shutdown Input
Input
V
Logic
Low (Regulator
ON)
0.6
2.0
0.7
2.0
0.7
2.0
V max
Voltage
High (Regulator
OFF)
V min
Shutdown Pin Input
Current
Vshutdown = 2.4V
30
450
3
50
100
600
750
10
30
450
3
50
100
600
750
10
30
450
3
50
100
600
750
10
µA max
µA max
µA max
µA max
µA max
µA max
Vshutdown = 30V
(Note 11)
Regulator Output
Current in Shutdown
20
20
20
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 = (V
+ 1)V, I = 100µA and C = 1µF for 5V versions and 2.2µF for 3V and 3.3V versions. Limits
L L
IN
ONOM
appearing in boldface type apply over the entire junction temperature range for operation. Limits appearing in normal type apply for T = T = 25˚C. Additional
A
J
conditions for the 8-pin versions are FEEDBACK tied to V
, OUTPUT tied to SENSE, and V
≤ 0.8V.
TAP
SHUTDOWN
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 NOM + 1)V. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = V /V = (R1 + R2)/R2.For example, at a
O
out ref
programmed output voltage of 5V, the Error output is guaranteed to go low when the output drops by 95mV x 5V/1.235V = 384 mV. Thresholds remain constant as
a percent of V as V is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.
out
out
Note 7: V ≤ V ≤ (V − 1V), 2.3V ≤ V ≤ 30V, 100µA ≤ I ≤ 100mA, T ≤ T .
JMAX
ref
out
in
in
L
J
Note 8: The junction-to-ambient thermal resistances are as follows: 180˚C/W and 160˚C/W for the TO-92 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 (N), 130˚C/W for the ceramic DIP (J), 160˚C/W for the molded plastic SOP (M), 200˚C/W for
the molded plastic MSOP (MM), and 160˚C/W for the metal can package (H). The above thermal resistances for the N, J, M, and MM packages apply when the
package is soldered directly to the PCB. Junction-to-case thermal resistance for the H package is 20˚C/W. Junction-to-case thermal resistance for the TO-252
package is 5.4˚C/W. The value of θ for the LLP package is typically 51˚C/W but is dependent on the PCB trace area, trace material, and the number of layers and
JA
thermal vias. For details of thermal resistance and power dissipation for the LLP package, refer to Application Note AN-1187.
Note 9: May exceed input supply voltage.
7
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Electrical Characteristics (Note 2) (Continued)
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
≥ 2V, V ≤ 30V, V = 0, Feedback pin tied to V
.
TAP
shutdown
in
out
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 V = 30V (1.25W pulse) for T = 10ms.
IN
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 = 1mA. For I = 100µA and T = 125˚C, line regulation is guaranteed by design to 0.2%. See Typical
L
L
J
Performance Characteristics for line regulation versus temperature and load current.
Note 16: A Military RETS specification is available on request. At time of printing, the LP2951 RETS specification complied with the boldface limits in this column.
The LP2951H, WG, or J may also be procured as Standard Military Drawing Spec #5962-3870501MGA, MXA, or MPA.
Note 17: 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 at this location of the part number (refer to ordering information table).
Note 18: Human Body Model 1.5kΩ in series with 100pF.
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8
Typical Performance Characteristics
Quiescent Current
Dropout Characteristics
00854627
00854628
Input Current
Input Current
00854629
00854630
Output Voltage vs. Temperature of 3
Representative Units
Quiescent Current
00854632
00854631
9
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Typical Performance Characteristics (Continued)
Quiescent Current
Quiescent Current
Short Circuit Current
Dropout Voltage
00854633
00854634
Quiescent Current
00854635
00854636
Dropout Voltage
00854638
00854637
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10
Typical Performance Characteristics (Continued)
LP2951 Minimum Operating Voltage
LP2951 Feedback Bias Current
00854639
00854640
LP2951 Feedback Pin Current
LP2951 Error Comparator Output
00854642
00854641
LP2951 Comparator Sink Current
Line Transient Response
00854643
00854644
11
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Typical Performance Characteristics (Continued)
Load Transient Response
Load Transient Response
Output Impedance
Ripple Rejection
00854645
00854646
00854648
00854650
LP2951 Enable Transient
00854647
Ripple Rejection
00854649
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12
Typical Performance Characteristics (Continued)
Ripple Rejection
LP2951 Output Noise
00854651
00854652
LP2951 Divider Resistance
Shutdown Threshold Voltage
00854653
00854654
Line Regulation
LP2951 Maximum Rated Output Current
00854655
00854656
13
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Typical Performance Characteristics (Continued)
LP2950 Maximum Rated Output Current
Thermal Response
00854657
00854658
Output Capacitor ESR Range
00854663
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14
Figure 1 below gives a timing diagram depicting the ERROR
signal and the regulated 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 = 4.75V).
Since the LP2951’s dropout voltage is load-dependent (see
curve in typical performance characteristics), the input volt-
age trip point (about 5V) will vary with the load current. The
output voltage trip point (approx. 4.75V) does not vary with
load.
Application Hints
EXTERNAL CAPACITORS
A 1.0µF (or greater) capacitor is required between the output
and ground for stability at output voltages of 5V or more. At
lower output voltages, more capacitance is required (2.2µF
or more is recommended for 3V and 3.3V versions). Without
this capacitor the part will oscillate. Most types of tantalum or
aluminum electrolytics work fine here; even film types work
but are not recommended for reasons of cost. Many alumi-
num electrolytics 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 5Ω or less and a resonant frequency above
500kHz. The value of this capacitor may be increased with-
out limit.
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 depend-
ing on system requirements. 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 1 MΩ. The resistor is
not required if this output is unused.
Ceramic capacitors whose value is greater than 1000pF
should not be connected directly from the LP2951 output to
ground. Ceramic capacitors typically have ESR values in the
range of 5 to 10mΩ, a value below the lower limit for stable
operation (see curve Output Capacitor ESR Range).
The reason for the lower ESR limit is that the loop compen-
sation of the part relies on the ESR of the output capacitor to
provide the zero that gives added phase lead. The ESR of
ceramic capacitors is so low that this phase lead does not
occur, significantly reducing phase margin. A ceramic output
capacitor can be used if a series resistance is added (rec-
ommended value of resistance about 0.1Ω to 2Ω).
At lower values of output current, less output capacitance is
required for stability. The capacitor can be reduced to 0.33µF
for currents below 10mA or 0.1µF for currents below 1mA.
Using the adjustable versions at voltages below 5V runs the
error amplifier at lower gains so that more output capaci-
tance 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.
00854620
*When V ≤ 1.3V, the error flag pin becomes a high impedance, and the
IN
error flag voltage rises to its pull-up voltage. Using V
as the pull-up
OUT
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
divide down the error flag voltage using equal-value resistors (10kΩ
suggested), to ensure a low-level logic signal during any fault condition,
while still allowing a valid high logic level during normal operation.
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 versions with external resistors, a minimum load
of 1µA is recommended.
FIGURE 1. ERROR Output Timing
PROGRAMMING THE OUTPUT VOLTAGE (LP2951)
The LP2951 may be pin-strapped for the nominal fixed out-
put voltage using its internal voltage divider by tying the
output and sense pins together, and also tying the feedback
and VTAP 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.
A 1µF tantalum, ceramic or aluminum electrolytic 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 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 fix
this problem.
The complete equation for the output voltage is
ERROR DETECTION COMPARATOR OUTPUT
The comparator produces a logic low output whenever the
LP2951 output falls out of regulation by more than approxi-
mately 5%. This figure is the comparator’s built-in offset of
about 60mV 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 pro-
grammed 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 limit-
ing.
where VREF is the nominal 1.235 reference voltage and IFB is
the feedback pin bias current, nominally −20nA. The mini-
mum recommended load current of 1µA 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 = 100k reduces this error to 0.17% while in-
creasing the resistor program current to 12µA. Since the
LP2951 typically draws 60µA at no load with Pin 2 open-
circuited, this is a small price to pay.
15
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Application Hints (Continued)
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 way noise can be reduced on the
3 lead LP2950 but 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
or about 0.01µF. When doing this, the output capacitor must
be increased to 3.3µF 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.
00854607
*See Application Hints
**Drive with TTL-high to shut down. Ground or leave open if shutdown
feature is not to be used.
Note: Pins 2 and 6 are left open.
FIGURE 2. Adjustable Regulator
Typical Applications
1A Regulator with 1.2V Dropout
00854622
300mA Regulator with 0.75V Dropout
Wide Input Voltage Range Current Limiter
00854621
00854609
*Minimum input-output voltage ranges from 40mV to 400mV, depending on
load current. Current limit is typically 160mA.
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16
Typical Applications (Continued)
Low Drift Current Source
5 Volt Current Limiter
00854610
*Minimum input-output voltage ranges from 40mV to 400mV, depending on
load current. Current limit is typically 160mA.
00854608
Regulator with Early Warning and Auxiliary Output
Latch Off When Error Flag Occurs
00854612
00854611
j
j
j
j
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 is programmed one diode drop above 5V. Its
out
error flag becomes active when V ≤ 5.7V. When V drops below 5.3V, the
in
in
error flag of Reg. #2 becomes active and via Q1 latches the main output off.
When V again exceeds 5.7V Reg. #1 is back in regulation and the early
in
warning signal rises, unlatching Reg. #2 via D3.
17
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Typical Applications (Continued)
2 Ampere Low Dropout Regulator
00854613
For 5V , use internal resistors. Wire pin 6 to 7, & wire pin 2 to +V Bus.
out
out
→
Open Circuit Detector for 4
20mA Current Loop
5V Regulator with 2.5V Sleep Function
00854615
00854614
*High input lowers V to 2.5V
out
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18
Typical Applications (Continued)
Regulator with State-of-Charge Indicator
00854616
*Optional Latch off when drop out occurs. Adjust R3 for C2 Switching when V is 6.0V.
in
**Outputs go low when V drops below designated thresholds.
in
Low Battery Disconnect
00854617
<
For values shown, Regulator shuts down when V
*Sets disconnect Voltage
5.5V and turns on again at 6.0V. Current drain in disconnected mode is ≈ 150µA.
in
**Sets disconnect Hysteresis
19
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Typical Applications (Continued)
System Overtemperature Protection Circuit
00854618
LM34 for 125˚F Shutdown
LM35 for 125˚C Shutdown
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20
21
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Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LP2951WG/883
NS Package Number WG10A
Metal Can Package (H)
NS Package Number H08C
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22
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Ceramic Dual-In-Line Package (J)
NS Package Number J08A
Surface Mount Package (M)
NS Package Number M08A
23
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Molded Dual-In-Line Package (N)
NS Package Number N08E
Molded TO-92 Package (Z)
NS Package Number Z03A
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24
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Surface Mount Package (MM)
NS Package Number MUA08A
D-Pak Package
NS Package Number TD03B
25
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
LLP Package
NS Package Number SDC08A
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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