LM397
LM397 Single General Purpose Voltage Comparator
Literature Number: SNOS977C
LM397
Single General Purpose Voltage Comparator
General Description
The LM397 is a single voltage comparator with an input
common mode that includes ground. The LM397 is designed
to operate from a single 5V to 30V power supply or a split
power supply. Its low supply current is virtually independent
of the magnitude of the supply voltage.
The LM397 features an open collector output stage. This
allows the connection of an external resistor at the output.
The output can directly interface with TTL, CMOS and other
logic levels, by tying the resistor to different voltage levels
(level translator).
The LM397 is available in space saving 5-Pin SOT23 pack-
age and pin compatible to TI’s TL331, single differential
comparator.
Features
(T
A
= 25˚C. Typical values unless otherwise specified).
n5-Pin SOT23 package
nIndustrial operating range −40˚C to +85˚C
nSingle or dual power supplies
nWide supply voltage range 5V to 30V
nLow supply current 300µA
nLow input bias current 7nA
nLow input offset current ±1nA
nLow input offset voltage ±2mV
nResponse time 440ns (50mV overdrive)
nInput common mode voltage 0 to V
S
- 1.5V
Applications
nA/D converters
nPulse, square wave generators
nPeak detector
nIndustrial applications
Connection Diagram
5-Pin SOT23
20022108
Top View
Typical Circuit
Ordering Information
Package Part Number Package Marking Transport Media NSC Drawing
5-Pin SOT-23 LM397MF C397 1k Units Tape and Reel MF05A
LM397MFX 3k Units Tape and Reel
20022109
FIGURE 1. Inverting Comparator with Hysteresis
August 2006
LM397 Single General Purpose Voltage Comparator
© 2006 National Semiconductor Corporation DS200221 www.national.com
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ESD Tolerance (Note 2)
Human Body Model 2KV
Machine Model 200V
V
IN
Differential 30V
Supply Voltages 30V or ±15V
Voltage at Input Pins −0.3V to 30V
Storage Temperature Range −65˚C to +150˚C
Junction Temperature (Note 3) +150˚C
Soldering Information
Infrared or Convection (20 sec.) 235˚C
Wave Soldering (10 sec.) 260˚C
Operating Ratings (Note 1)
Supply Voltage, V
S
5V to 30V
Temperature Range (Note 3) −40˚C to +85˚C
Package Thermal Resistance (Note 3)
5-Pin SOT23 168˚C/W
Electrical Characteristics Unless otherwise specified, all limits are guaranteed for T
A
= 25˚C, V
S
= 5V, V
−
=
0V, V
CM
=V
+
/2=V
O
.Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 5)
Typ
(Note 4)
Max
(Note 5)
Units
V
OS
Input Offset Voltage V
S
= 5V to 30V,
V
O
= 1.4V, V
CM
=0V
27
10
mV
I
OS
Input Offset Current V
O
= 1.4V, V
CM
= 0V 1.6 50
250
nA
I
B
Input Bias Current V
O
= 1.4V, V
CM
= 0V 10 250
400
nA
I
S
Supply Current R
L
= Open, V
S
= 5V 0.25 0.7 mA
R
L
= Open, V
S
= 30V 0.30 2
I
O
Output Sink Current V
IN
+= 1V,V
IN
−= 0V, V
O
= 1.5V 6 13 mA
I
LEAKAGE
Output Leakage Current V
IN
+= 1V,V
IN
−= 0V, V
O
= 5V 0.1 nA
V
IN
+= 1V,V
IN
−= 0V, V
O
= 30V 1 µA
V
OL
Output Voltage Low I
O
= −4mA, V
IN
+= 0V,V
IN
−= 1V 180 400
700
mV
V
CM
Common-Mode Input Voltage
Range
V
S
= 5V to 30V (Note 6) 0
0
V
S
- 1.5V
V
S
-2V V
A
V
Voltage Gain V
S
= 15V, V
O
= 1.4V to 11.4V,
R
L
>= 15kΩconnected to V
S
120 V/mV
t
PHL
Propagation Delay
(High to Low)
Input Overdrive = 5mV
R
L
= 5.1kΩconnected to 5V, C
L
= 15pF
900
ns
Input Overdrive = 50mV
R
L
= 5.1kΩconnected to 5V, C
L
= 15pF
250
t
PLH
Propagation Delay
(Low to High)
Input Overdrive = 5mV
R
L
= 5.1kΩconnected to 5V, C
L
= 15pF
940 µs
Input Overdrive = 50mV
R
L
= 5.1kΩconnected to 5V, C
L
= 15pF
440 ns
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.
Note 2: Human Body Model, applicable std. MIL-STD-883, Method 3015.7. Machine Model, applicable std. JESD22-A115-A (ESD MM std. of JEDEC)
Field-Induced Charge-Device Model, applicable std. JESD22-C101-C (ESD FICDM std. of JEDEC).
Note 3: The maximum power dissipation is a function of TJ(MAX),θJA. The maximum allowable power dissipation at any ambient temperature is
PD=(T
J(MAX) -T
A)/ θJA . All numbers apply for packages soldered directly onto a PC board.
Note 4: Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary over time and will
also depend on the application and configuration. The typical values are not tested and are not guaranteed on shipped production material.
Note 5: All limits are guaranteed by testing or statistical analysis.
Note 6: The input common-mode voltage of either input should not be permitted to go below the negative rail by more than 0.3V. The upper end of the
common-mode voltage range is VS- 1.5V at 25˚C.
LM397
www.national.com 2
Typical Performance Characteristics T
A
= 25˚C. Unless otherwise specified.
Supply Current vs. Supply Voltage Input Bias Current vs. Supply Current
20022103 20022101
Output Saturation Voltage vs. Output Sink Current Input Offset Voltage vs. Supply Voltage
20022104 20022102
Response Time for Various Input Overdrives – t
PHL
Response Time for Various Input Overdrives – t
PLH
20022105 20022106
LM397
www.national.com3
Application Notes
Basic Comparators
A comparator is quite often used to convert an analog signal
to a digital signal. The comparator compares an input volt-
age (V
IN
) at the non-inverting pin to the reference voltage
(V
REF
) at the inverting pin. If V
IN
is less than V
REF
the output
(V
O
) is low (V
OL
). However, if V
IN
is greater than V
REF
, the
output voltage (V
O
) is high (V
OH
). Refer to Figure 2.
Hysteresis
The basic comparator configuration may oscillate or produce
a noisy output if the applied differential input is near the
comparator’s input offset voltage. This tends to occur when
the voltage on the input is equal or very close to the other
input voltage. Adding hysteresis can prevent this problem.
Hysteresis creates two switching thresholds (one for the
rising input voltage and the other for the falling input volt-
age). Hysteresis is the voltage difference between the two
switching thresholds. When both inputs are nearly equal,
hysteresis causes one input to effectively move quickly pass
the other. Thus, effectively moving the input out of region that
oscillation may occur.
For an inverting configured comparator, hysteresis can be
added with a three resistor network and positive feedback.
When input voltage (V
IN
) at the inverting node is less than
non-inverting node (V
T
), the output is high. The equivalent
circuit for the three resistor network is R
1
in parallel with R
3
and in series with R
2
. The lower threshold voltage V
T1
is
calculated by:
V
T1
= ((V
S
R
2
) / (((R
1
R
3
)/(R
1
+R
3
))+R
2
))
When V
IN
is greater than V
T
, the output voltage is low. The
equivalent circuit for the three resistor network is R
2
in
parallel with R
3
and in series with R
1
. The upper threshold
voltage V
T2
is calculated by:
V
T2
=V
S
((R
2
R
3
)/(R
2
+R
3
))/(R
1
+ ((R
2
R
3
)/(R
2
+
R
3
)))
The hysteresis is defined as
∆V
IN
=V
T1
–V
T2
20022110
20022111
FIGURE 2. Basic Comparator
20022112
20022113
FIGURE 3. Inverting Configured Comparator – LM397
LM397
www.national.com 4
Application Notes (Continued)
Input Stage
The LM397 has a bipolar input stage. The input common
mode voltage range is from 0 to (V
S
– 1.5V).
Output Stage
The LM397 has an open collector grounded-emitter NPN
output transistor for the output stage. This requires an exter-
nal pull-up resistor connected between the positive supply
voltage and the output. The external pull-up resistor should
be high enough resistance so to avoid excessive power
dissipation. In addition, the pull-up resistor should be low
enough resistance to enable the comparator to switch with
the load circuitry connected. Because it is an open collector
output stage, several comparator outputs can be connected
together to create an OR’ing function output. With an open
collector, the output can be used as a simple SPST switch to
ground.The amount of current which the output can sink is
approximately 10mA. When the maximum current limit is
reached, the output transistor will saturate and the output will
rise rapidly (Figure 4).
20022107
FIGURE 4. Output Saturation Voltage vs. Output Sink
Current
LM397
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SOT23-5 Tape and Reel Specification
Tape Format
Tape Section #Cavities Cavity Status Cover Tape Status
Leader (Start End) 0 (min) Empty Sealed
75 (min) Empty Sealed
Carrier 3000 Filled Sealed
1000 Filled Sealed
Trailer (Hub End) 125 (min) Empty Sealed
0 (min) Empty Sealed
TAPE DIMENSIONS
20022115
8mm 0.130
(3.3)
0.124
(3.15)
0.130
(3.3)
0.126
(3.2)
0.138 ±0.002
(3.5 ±0.05)
0.055 ±0.004
(1.4 ±0.11)
0.157
(4)
0.315 ±0.012
(8 ±0.3)
Tape Size DIM A DIM Ao DIM B DIM Bo DIM F DIM Ko DIM P1 DIM W
LM397
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SOT23-5 Tape and Reel Specification (Continued)
REEL DIMENSIONS
20022116
8mm 7.00
330.00
0.059
1.50
0.512
13.00
0.795
20.20
2.165
55.00
0.331 + 0.059/−0.000
8.40 + 1.50/−0.00
0.567
14.40
W1 + 0.078/−0.039
W1 + 2.00/−1.00
Tape Size A B C D N W1 W2 W3
LM397
www.national.com7
Physical Dimensions inches (millimeters) unless otherwise noted
5-Pin SOT23
NS Package Number MF05A
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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www.national.com
LM397 Single General Purpose Voltage Comparator
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