LM4431
Micropower Shunt Voltage Reference
General Description
Ideal for space critical applications, the LM4431 voltage ref-
erence is available in the sub-miniature (3 mm x 1.3 mm)
SOT-23 surface-mount package. The LM4431's advanced
design eliminates the need for an external stabilizing capaci-
tor while ensuring stability with any capacitive load, thus
making the LM4431 easy to use. The operating current
range is 100 A to 15 mA.
The LM4431 utilizes fuse and zener-zap reverse breakdown
voltage trim during wafer sort to ensure that the parts have
an accuracy of better than
2.0% at 25C. Bandgap refer-
ence temperature drift curvature correction and low dynamic
impedance ensure stable reverse breakdown voltage accu-
racy over a wide range of operating temperatures and cur-
rents.
Features
n
Small package: SOT-23
n
No output capacitor required
n
Tolerates capacitive loads
n
Fixed reverse breakdown voltage of 2.50V
Key Specifications
n
Output voltage tolerance 25C:
2.0% (max)
n
Low output noise (10 Hz to 10 kHz): 35 V
rms
(typ)
n
Wide operating current range: 100 A to 15 mA
n
Commercial temperature range: 0C to +70C
n
Low temperature coefficient: 30 ppm/C (typ)
Applications
n
Portable, Battery-Powered Equipment
n
Data Acquisition Systems
n
Instrumentation
n
Process Control
n
Energy Management
n
Product Testing
n
Power Supplies
Connection Diagram
SOT-23 Package Marking Information
Only three fields of marking are possible on the SOT-23's small surface. The following table gives the meaning of the three
fields.
Part Marking
Field Definition
S2E
First Field:
S = Reference
Second Field:
2 = 2.500V Voltage Option
Third Field:
E = Initial Reverse Breakdown Voltage Tolerance of
2.0%
SOT-23
DS011374-1
* This pin must be left floating or connected to pin 2.
Top View
Order Number LM4431M3-2.5
See NS Package Number M03B
(JEDEC Registration TO-236AB)
July 1998
LM4431
Micropower
Shunt
V
oltage
Reference
1998 National Semiconductor Corporation
DS011374
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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.
Reverse Current
20 mA
Forward Current
10 mA
Power Dissipation (T
A
= 25C) (Note 2)
M3 Package
306 mW
Storage Temperature
-65C to +150C
Lead Temperature
M3 Package
Vapor phase (60 seconds)
+215C
Infrared (15 seconds)
+220C
ESD Susceptibility
Human Body Model (Note 3)
2 kV
Machine Model (Note 3)
200V
See AN-450 "Surface Mounting Methods and Their Effect
on Product Reliability" for other methods of soldering
surface mount devices.
Operating Ratings
(Notes 1, 2)
Temperature Range
(T
min
T
A
T
max
)
0C
T
A
+70C
Reverse Current
LM4431-2.5
100 A to 15 mA
LM4431-2.5
Electrical Characteristics
Boldface limits apply for T
A
= T
J
= T
MIN
to T
MAX
; all other limits T
A
= T
J
= 25C.
Symbol
Parameter
Conditions
Typical
LM4431M3
Units
(Note 4)
Limits
(Limit)
(Note 5)
V
R
Reverse Breakdown Voltage
I
R
= 100 A
2.500
V
Reverse Breakdown
VoltageTolerance
I
R
= 100 A
50
mV (max)
I
RMIN
Minimum Operating Current
45
A
100
A (max)
V
R
/
T
Average Reverse Breakdown
I
R
= 10 mA
30
ppm/C
Voltage Temperature
I
R
= 1 mA
30
ppm/C
Coefficient
I
R
= 100 A
30
ppm/C
V
R
/
I
R
Reverse Breakdown Voltage
I
RMIN
I
R
1 mA
0.4
mV
Change with Operating
1.0
mV (max)
Current Change
1.2
mV (max)
1 mA
I
R
15 mA
2.5
mV
8.0
mV (max)
25
mV (max)
Z
R
Reverse Dynamic Impedance
I
R
= 1 mA, f = 120 Hz
1.0
I
AC
= 0.1 I
R
e
N
Wideband Noise
I
R
= 100 A
35
V
rms
10 Hz
f
10 kHz
V
R
Reverse Breakdown Voltage
t = 1000 hrs
Long Term Stability
T = 25C
0.1C
120
ppm
I
R
= 100 A
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is func-
tional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed speci-
fications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions.
Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
Jmax
(maximum junction temperature),
JA
(junction to am-
bient thermal resistance), and T
A
(ambient temperature). The maximum allowable power dissipation at any temperature is PD
max
= (T
Jmax
- T
A
)/
JA
or the number
given in the Absolute Maximum Ratings, whichever is lower. For the LM4431, T
Jmax
= 125C, and the typical thermal resistance (
JA
), when board mounted, is
326C/W for the SOT-23 package.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 k
resistor into each pin. The machine model is a 200 pF capacitor discharged di-
rectly into each pin.
Note 4: Typicals are at T
J
= 25C and represent most likely parametric norm.
Note 5: Limits are 100% production tested at 25C. Limits over temperature are guaranteed through correlation using Statistical Quality Control (SQC) methods. The
limits are used to calculate National's AOQL.
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2
Typical Performance Characteristics
Start-Up Characteristics
Temperature Drift for Different
Average Temperature Coefficient
DS011374-2
Output Impedance vs Frequency
DS011374-3
Reverse Characteristics and
Minimum Operating Current
DS011374-4
Noise Voltage
DS011374-5
DS011374-6
LM4431-2.5
R
S
= 30k
DS011374-7
3
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Functional Block Diagram
Applications Information
The LM4431 is a micro-power curvature-corrected 2.5V
bandgap shunt voltage reference. For space critical applica-
tions, the LM4431 is available in the sub-miniature SOT-23
surface-mount package. The LM4431 has been designed for
stable operation without the need of an external capacitor
connected between the "+" pin and the "-" pin. If, however, a
bypass capacitor is used, the LM4431 remains stable. The
operating current range is 100 A to 15 mA.
The LM4431's SOT-23 package has a parasitic Schottky di-
ode between pin 2 (-) and pin 3 (Die attach interface con-
tact). Therefore, pin 3 of the SOT-23 package must be left
floating or connected to pin 2.
In a conventional shunt regulator application (
Figure 1) , an
external series resistor (R
S
) is connected between the sup-
ply voltage and the LM4431. R
S
determines the current that
flows through the load (I
L
) and the LM4431 (I
Q
). Since load
current and supply voltage may vary, R
S
should be small
enough to supply at least the minimum acceptable I
Q
to the
LM4431 even when the supply voltage is at its minimum and
the load current is at its maximum value. When the supply
voltage is at its maximum and I
L
is at its minimum, R
S
should
be large enough so that the current flowing through the
LM4431 is less than 15 mA.
R
S
is determined by the supply voltage, (V
S
), the load and
operating current, (I
L
and I
Q
), and the LM4431's reverse
breakdown voltage, V
R
.
Typical Applications
DS011374-8
DS011374-9
FIGURE 1. Shunt Regulator
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4
Typical Applications
(Continued)
DS011374-10
FIGURE 2. Bounded amplifier reduces saturation-induced delays and can prevent succeeding stage damage.
Nominal clamping voltage is
3.9V (LM4431's reverse breakdown voltage +2 diode V
F
).
DS011374-11
FIGURE 3. Protecting Op Amp input. The bounding voltage is
4V with the LM4431
(LM4431's reverse breakdown voltage + 3 diode V
F
).
5
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