LM2931
Series Low Dropout Regulators
General Description
The LM2931 positive voltage regulator features a very low
quiescent current of 1mA or less when supplying 10mA
loads. This unique characteristic and the extremely low
input-output differential required for proper regulation (0.2V
for output currents of 10mA) make the LM2931 the ideal
regulator for standby power systems. Applications include
memory standby circuits, CMOS and other low power pro-
cessor power supplies as well as systems demanding as
much as 100mA of output current.
Designed originally for automotive applications, the LM2931
and all regulated circuitry are protected from reverse battery
installations or 2 battery jumps. During line transients, such
as a load dump (60V) when the input voltage to the regulator
can momentarily exceed the specified maximum operating
voltage, the regulator will automatically shut down to protect
both internal circuits and the load. The LM2931 cannot be
harmed by temporary mirror-image insertion. Familiar regu-
lator features such as short circuit and thermal overload
protection are also provided.
The LM2931 family includes a fixed 5V output (±3.8% toler-
ance for A grade) or an adjustable output with ON/OFF pin.
Both versions are available in a TO-220 power package,
TO-263 surface mount package, and an 8-lead surface
mount package. The fixed output version is also available in
the TO-92 plastic and 6-Bump micro SMD packages.
Features
nVery low quiescent current
nOutput current in excess of 100 mA
nInput-output differential less than 0.6V
nReverse battery protection
n60V load dump protection
n−50V reverse transient protection
nShort circuit protection
nInternal thermal overload protection
nMirror-image insertion protection
nAvailable in TO-220, TO-92, TO-263, SO-8 or 6-Bump
micro SMD packages
nAvailable as adjustable with TTL compatible switch
nSee AN-1112 for micro SMD considerations
Connection Diagrams
FIXED VOLTAGE OUTPUT
TO-220 3-Lead Power Package
00525406
Front View
TO-263 Surface-Mount Package
00525411
Top View
00525412
Side View
8-Pin Surface Mount TO-92 Plastic Package
00525407
Top View
*NC = Not internally connected. Must be electrically isolated from the rest
of the circuit for the micro SMD package.
00525408
Bottom View
March 2002
LM2931 Series Low Dropout Regulators
© 2002 National Semiconductor Corporation DS005254 www.national.com
Connection Diagrams (Continued)
6-Bump micro SMD micro SMD Laser Mark
00525438
Top View
(Bump Side Down)
00525439
ADJUSTABLE OUTPUT VOLTAGE
TO-220 5-Lead Power Package
00525409
Front View
TO-263
5-Lead Surface-Mount Package
00525413
Top View
00525414
Side View
8-Pin Surface Mount
00525410
Top View
LM2931
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Ordering Information
Output
Number Package Part Number Package Marking Transport Media NSC Drawing
5V 3-Pin TO-220 LM2931T-5.0 LM2931T-5.0 Rails T03B
LM2931AT-5.0 LM2931AT-5.0 Rails
3-Pin TO-263 LM2931S-5.0 LM2931S-5.0 Rails TS3B
LM2931AS-5.0 LM2931AS-5.0 Rails
TO-92 LM2931Z-5.0 LM2931Z-5 1.8k Units per Box Z03A
LM2931AZ-5.0 LM2931AZ 1.8k Units per Box
8-Pin
SOIC LM2931M-5.0 2931M-5.0 Rails M08A
LM2931AM-5.0 2931AM-5.0 Rails
*6-Bump
micro SMD LM2931IBPX-5.0 - Tape and Reel BPA06HTA
Adjustable,
3V to 24V 5-Pin TO-220 LM2931CT LM2931CT Rails T05A
5-Pin TO-263 LM2931CS LM2931CS Rails TS5B
8-Pin
SOIC LM2931CM LM2931CM Rails M08A
3.3V *6-Bump
micro SMD LM2931IBPX-3.3 - Tape and Reel BPA06HTB
Note: The micro SMD package marking is a single digit manufacturing Date
Code Only.
LM2931
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Typical Applications
LM2931 Fixed Output
00525404
*Required if regulator is located far from power supply filter.
**C2 must be at least 100 µF to maintain stability. May be increased without bound to maintain regulation during transients. Locate as close as possible to the
regulator. This capacitor must be rated over the same operating temperature range as the regulator. The equivalent series resistance (ESR) of this capacitor is
critical; see curve.
LM2931 Adjustable Output
00525405
Note: Using 27k for R1 will automatically compensate for errors in VOUT due to the input bias current of the ADJ pin (approximately 1 µA).
LM2931
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Voltage
Operating Range 26V
Overvoltage Protection
LM2931A, LM2931C
(Adjustable) 60V
LM2931 50V
Internal Power Dissipation
(Note 2) (Note 4) Internally Limited
Operating Ambient Temperature
Range −40˚C to +85˚C
Maximum Junction Temperature 125˚C
Storage Temperature Range −65˚C to +150˚C
Lead Temp. (Soldering, 10 seconds) 230˚C
ESD Tolerance (Note 5) 2000V
Electrical Characteristics for Fixed 3.3V Version
V
IN
= 14V, I
O
= 10mA, T
J
= 25˚C, C
2
= 100µF (unless otherwise specified) (Note 2)
Parameter Conditions LM2931-3.3 Units
Typ Limit
(Note 3)
Output Voltage 3.3 3.465
3.135 V
MAX
V
MIN
4V ≤V
IN
≤26V, I
O
= 100 mA
−40˚C ≤T
J
≤125˚C 3.630
2.970 V
MAX
V
MIN
Line Regulation 4V ≤V
IN
≤26V 4 33 mV
MAX
Load Regulation 5mA ≤I
O
≤100mA 10 50 mV
MAX
Output Impedance 100mA
DC
and 10mA
rms
,
100Hz - 10kHz 200 mΩ
Quiescent Current I
O
≤10mA, 4V ≤V
IN
≤26V 0.4 1.0 mA
MAX
−40˚C ≤T
J
≤125˚C
I
O
= 100mA, V
IN
= 14V, T
J
= 25˚C 15 mA
Output Noise Voltage 10Hz -100kHz, C
OUT
= 100µF 330 µV
rms
Long Term Stability 13 mV/1000 hr
Ripple Rejection f
O
= 120Hz 80 dB
Dropout Voltage I
O
= 10mA
I
O
= 100mA 0.05
0.30 0.2
0.6 V
MAX
Maximum Operational Input
Voltage 33 26 V
MIN
Maximum Line Transient R
L
= 500Ω,V
O
≤5.5V,
T = 1ms, τ≤100ms 70 50 V
MIN
Reverse Polarity Input
Voltage, DC V
O
≥−0.3V, R
L
= 500Ω−30 −15 V
MIN
Reverse Polarity Input
Voltage, Transient T = 1ms, τ≤100ms, R
L
= 500Ω−80 −50 V
MIN
Electrical Characteristics for Fixed 5V Version
V
IN
= 14V, I
O
= 10mA, T
J
= 25˚C, C2 = 100 µF (unless otherwise specified) (Note 2)
Parameter Conditions LM2931A-5.0 LM2931-5.0 Units
Typ Limit
(Note 3) Typ Limit
(Note 3)
Output Voltage 5 5.19
4.81 5 5.25
4.75 V
MAX
V
MIN
6.0V ≤V
IN
≤26V, I
O
= 100mA
−40˚C ≤T
J
≤125˚C 5.25
4.75 5.5
4.5 V
MAX
V
MIN
Line Regulation 9V ≤V
IN
≤16V
6V ≤V
IN
≤26V 2
410
30 2
410
30 mV
MAX
LM2931
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Electrical Characteristics for Fixed 5V Version (Continued)
V
IN
= 14V, I
O
= 10mA, T
J
= 25˚C, C2 = 100 µF (unless otherwise specified) (Note 2)
Parameter Conditions LM2931A-5.0 LM2931-5.0 Units
Typ Limit
(Note 3) Typ Limit
(Note 3)
Load Regulation 5 mA ≤I
O
≤100mA 14 50 14 50 mV
MAX
Output Impedance 100mA
DC
and 10mA
rms
,
100Hz -10kHz 200 200 mΩ
Quiescent Current I
O
≤10mA, 6V ≤V
IN
≤26V 0.4 1.0 0.4 1.0 mA
MAX
−40˚C ≤T
J
≤125˚C
I
O
= 100mA, V
IN
= 14V, T
J
= 25˚C 15 30
515 mA
MAX
mA
MIN
Output Noise Voltage 10Hz -100kHz, C
OUT
= 100µF 500 500 µV
rms
Long Term Stability 20 20 mV/1000
hr
Ripple Rejection f
O
= 120 Hz 80 55 80 dB
MIN
Dropout Voltage I
O
= 10mA
I
O
= 100mA 0.05
0.3 0.2
0.6 0.05
0.3 0.2
0.6 V
MAX
Maximum Operational Input
Voltage 33 26 33 26 V
MIN
Maximum Line Transient R
L
= 500Ω,V
O
≤5.5V,
T = 1ms, τ≤100ms 70 60 70 50 V
MIN
Reverse Polarity Input
Voltage, DC V
O
≥−0.3V, R
L
= 500Ω−30 −15 −30 −15 V
MIN
Reverse Polarity Input
Voltage, Transient T = 1ms, τ≤100ms, R
L
= 500Ω−80 −50 −80 −50 V
MIN
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions.
Note 2: See circuit in Typical Applications. To ensure constant junction temperature, low duty cycle pulse testing is used.
Note 3: All limits are guaranteed for TJ= 25˚C (standard type face) or over the full operating junction temperature range of −40˚C to +125˚C (bold type face).
Note 4: The maximum power dissipation is a function of maximum junction temperature TJmax, total thermal resistance θJA, and ambient temperature TA. The
maximum allowable power dissipation at any ambient temperature is PD=(T
Jmax −T
A
)/θJA. If this dissipation is exceeded, the die temperature will rise above 150˚C
and the LM2931 will go into thermal shutdown. For the LM2931 in the TO-92 package, θJA is 195˚C/W; in the SO-8 package, θJA is 160˚C/W, and in the TO-220
package, θJA is 50˚C/W; in the TO-263 package, θJA is 73˚C/W; and in the 6-Bump micro SMD package θJA is 290˚C/W. If the TO-220 package is used with a heat
sink, θJA is the sum of the package thermal resistance junction-to-case of 3˚C/W and the thermal resistance added by the heat sink and thermal interface.
If the TO-263 package is used, the thermal resistance can be reduced by increasing the P.C. board copper area thermally connected to the package: Using 0.5
square inches of copper area, θJA is 50˚C/W; with 1 square inch of copper area, θJA is 37˚C/W; and with 1.6 or more square inches of copper area, θJA is 32˚C/W.
Note 5: Human body model, 100 pF discharged through 1.5 kΩ.
Electrical Characteristics for Adjustable Version
V
IN
= 14V, V
OUT
= 3V, I
O
= 10 mA, T
J
= 25˚C, R1 = 27k, C2 = 100 µF (unless otherwise specified) (Note 2)
Parameter Conditions Typ Limit Units
Limit
Reference Voltage 1.20 1.26 V
MAX
1.14 V
MIN
I
O
≤100 mA, −40˚C ≤T
j
≤125˚C, R1 = 27k 1.32 V
MAX
Measured from V
OUT
to Adjust Pin 1.08 V
MIN
Output Voltage Range 24 V
MAX
3V
MIN
Line Regulation V
OUT
+ 0.6V ≤V
IN
≤26V 0.2 1.5 mV/V
MAX
Load Regulation 5 mA ≤I
O
≤100 mA 0.3 1 %
MAX
Output Impedance 100 mA
DC
and 10 mA
rms
, 100 Hz–10 kHz 40 mΩ/V
Quiescent Current I
O
= 10 mA 0.4 1 mA
MAX
I
O
= 100 mA 15 mA
During Shutdown R
L
= 500Ω0.8 1 mA
MAX
LM2931
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Electrical Characteristics for Adjustable Version (Continued)
V
IN
= 14V, V
OUT
= 3V, I
O
= 10 mA, T
J
= 25˚C, R1 = 27k, C2 = 100 µF (unless otherwise specified) (Note 2)
Parameter Conditions Typ Limit Units
Limit
Output Noise Voltage 10 Hz–100 kHz 100 µV
rms
/V
Long Term Stability 0.4 %/1000 hr
Ripple Rejection f
O
= 120 Hz 0.02 %/V
Dropout Voltage I
O
≤10 mA 0.05 0.2 V
MAX
I
O
= 100 mA 0.3 0.6 V
MAX
Maximum Operational Input
Voltage 33 26 V
MIN
Maximum Line Transient I
O
= 10 mA, Reference Voltage ≤1.5V 70 60 V
MIN
T=1ms,τ≤100 ms
Reverse Polarity Input V
O
≥−0.3V, R
L
= 500Ω
Voltage, DC −30 −15 V
MIN
Reverse Polarity Input T = 1 ms, τ≤100 ms, R
L
= 500Ω
Voltage, Transient −80 −50 V
MIN
On/Off Threshold Voltage V
O
=3V
On 2.0 1.2 V
MAX
Off 2.2 3.25 V
MIN
On/Off Threshold Current 20 50 µA
MAX
LM2931
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Typical Performance Characteristics
Dropout Voltage Dropout Voltage
00525416 00525417
Low Voltage Behavior Output at Voltage Extremes
00525418 00525419
Line Transient Response Load Transient Response
00525420 00525421
LM2931
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Typical Performance Characteristics (Continued)
Peak Output Current Quiescent Current
00525422 00525423
Quiescent Current Quiescent Current
00525424 00525425
Ripple Rejection Ripple Rejection
00525426 00525427
LM2931
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Typical Performance Characteristics (Continued)
Output Impedance Operation During Load
Dump
00525428 00525429
Reference Voltage Maximum Power Dissipation
(SO-8)
00525430 00525431
Maximum Power Dissipation
(TO-220) Maximum Power Dissipation
(TO-92)
00525432 00525433
LM2931
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Schematic Diagram
00525401
LM2931
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Application Hints
One of the distinguishing factors of the LM2931 series regu-
lators is the requirement of an output capacitor for device
stability. The value required varies greatly depending upon
the application circuit and other factors. Thus some com-
ments on the characteristics of both capacitors and the
regulator are in order.
High frequency characteristics of electrolytic capacitors de-
pend greatly on the type and even the manufacturer. As a
result, a value of capacitance that works well with the
LM2931 for one brand or type may not necessary be suffi-
cient with an electrolytic of different origin. Sometimes actual
bench testing, as described later, will be the only means to
determine the proper capacitor type and value. Experience
has shown that, as a rule of thumb, the more expensive and
higher quality electrolytics generally allow a smaller value for
regulator stability. As an example, while a high-quality 100
µF aluminum electrolytic covers all general application cir-
cuits, similar stability can be obtained with a tantalum elec-
trolytic of only 47µF. This factor of two can generally be
applied to any special application circuit also.
Another critical characteristic of electrolytics is their perfor-
mance over temperature. While the LM2931 is designed to
operate to −40˚C, the same is not always true with all elec-
trolytics (hot is generally not a problem). The electrolyte in
many aluminum types will freeze around −30˚C, reducing
their effective value to zero. Since the capacitance is needed
for regulator stability, the natural result is oscillation (and lots
of it) at the regulator output. For all application circuits where
cold operation is necessary, the output capacitor must be
rated to operate at the minimum temperature. By coinci-
dence, worst-case stability for the LM2931 also occurs at
minimum temperatures. As a result, in applications where
the regulator junction temperature will never be less than
25˚C, the output capacitor can be reduced approximately by
a factor of two over the value needed for the entire tempera-
ture range. To continue our example with the tantalum elec-
trolytic, a value of only 22µF would probably thus suffice. For
high-quality aluminum, 47µF would be adequate in such an
application.
Another regulator characteristic that is noteworthy is that
stability decreases with higher output currents. This sensible
fact has important connotations. In many applications, the
LM2931 is operated at only a few milliamps of output current
or less. In such a circuit, the output capacitor can be further
reduced in value. As a rough estimation, a circuit that is
required to deliver a maximum of 10mA of output current
from the regulator would need an output capacitor of only
half the value compared to the same regulator required to
deliver the full output current of 100mA. If the example of the
tantalum capacitor in the circuit rated at 25˚C junction tem-
perature and above were continued to include a maximum of
10mAof output current, then the 22µF output capacitor could
be reduced to only 10µF.
In the case of the LM2931CT adjustable regulator, the mini-
mum value of output capacitance is a function of the output
voltage. As a general rule, the value decreases with higher
output voltages, since internal loop gain is reduced.
At this point, the procedure for bench testing the minimum
value of an output capacitor in a special application circuit
should be clear. Since worst-case occurs at minimum oper-
ating temperatures and maximum operating currents, the
entire circuit, including the electrolytic, should be cooled to
the minimum temperature. The input voltage to the regulator
should be maintained at 0.6V above the output to keep
internal power dissipation and die heating to a minimum.
Worst-case occurs just after input power is applied and
before the die has had a chance to heat up. Once the
minimum value of capacitance has been found for the brand
and type of electrolytic in question, the value should be
doubled for actual use to account for production variations
both in the capacitor and the regulator. (All the values in this
section and the remainder of the data sheet were deter-
mined in this fashion.)
LM2931 micro SMD Light Sensitivity
When the LM2931 micro SMD package is exposed to bright
sunlight, normal office fluorescent light, and other LED’s, it
operates within the guaranteed limits specified in the electri-
cal characteristic table.
Definition of Terms
Dropout Voltage: The input-output voltage differential at
which the circuit ceases to regulate against further reduction
in input voltage. Measured when the output voltage has
dropped 100 mV from the nominal value obtained at 14V
input, dropout voltage is dependent upon load current and
junction temperature.
Input Voltage: The DC voltage applied to the input terminals
with respect to ground.
Input-Output Differential: The voltage difference between
the unregulated input voltage and the regulated output volt-
age for which the regulator will operate.
Line Regulation: The change in output voltage for a change
in the input voltage. The measurement is made under con-
ditions of low dissipation or by using pulse techniques such
that the average chip temperature is not significantly af-
fected.
Load Regulation: The change in output voltage for a
change in load current at constant chip temperature.
Long Term Stability: Output voltage stability under accel-
erated life-test conditions after 1000 hours with maximum
rated voltage and junction temperature.
Output Noise Voltage: The rms AC voltage at the output,
with constant load and no input ripple, measured over a
specified frequency range.
Quiescent Current: That part of the positive input current
that does not contribute to the positive load current. The
regulator ground lead current.
Ripple Rejection: The ratio of the peak-to-peak input ripple
voltage to the peak-to-peak output ripple voltage at a speci-
fied frequency.
Temperature Stability of V
O
:The percentage change in
output voltage for a thermal variation from room temperature
to either temperature extreme.
LM2931
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Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead Surface Mount Package (M)
NS Package Number M08A
3-Lead TO-220 Plastic Package (T)
NS Package Number T03B
LM2931
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
5-Lead TO-220 Power Package (T)
NS Package Number T05A
3-Lead TO-263 Surface Mount Package
NS Package Number TS3B
LM2931
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
5-Lead TO-263 Surface Mount Package
NS Package Number TS5B
LM2931
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
3-Lead TO-92 Plastic Package (Z)
NS Package Number Z03A
LM2931
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
6-Bump micro SMD
NS Package Number BPA06HTB
X
1
= 0.955 X
2
= 1.717 X
3
= 0.850
NOTE: UNLESS OTHERWISE SPECIFIED.
1. EPOXY COATING.
2. 63Sn/37Pb EUTECTIC BUMP.
3. RECOMMEND NON-SOLDER MASK DEFINED LANDING PAD.
4. PIN A1 IS ESTABLISHED BY LOWER LEFT CORNER WITH RESPECT TO TEST ORIENTATION PINS ARE NUMBERED COUNTERCLOCKWISE.
5. XXX IN DRAWING NUMBER REPRESENTS PACKAGE SIZE VARIATION WHERE X1IS PACKAGE WIDTH, X2IS PACKAGE LENGTH AND X3IS
PACKAGE HEIGHT.
6. REFERENCE JEDEC REGISTRATION MO-211, VARIATION BC.
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
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Email: support@nsc.com
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Fax: 81-3-5639-7507
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LM2931 Series Low Dropout Regulators
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.
