LMV7291
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SNOSA86E – FEBRUARY 2004 – REVISED MARCH 2013
LMV7291 Single 1.8V Low Power Comparator with Rail-to-Rail Input
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FEATURES
DESCRIPTION
•
The LMV7291 is a rail-to-rail input low power
comparator, characterized at supply voltage 1.8V,
2.7V and 5.0V. It consumes only 9uA supply current
per channel while achieving a 800ns propagation
delay.
1
2
•
•
•
•
•
•
•
(VS = 1.8V, TA = 25°C, Typical
Values unless Specified)
Single Supply
Ultra Low Supply Current 9µA per Channel
Low Input Bias Current 10nA
Low Input Offset Current 200pA
Low ensured VOS 4mV
Propagation Delay 880ns (20mV Overdrive)
Input Common Mode Voltage Range 0.1V
beyond Rails
The LMV7291 is available in SC70 package. With this
tiny package, the PC board area can be significantly
reduced. It is ideal for low voltage, low power and
space critical designs.
The LMV7291 features a push-pull output stage
which allows operation with minimum power
consumption when driving a load.
The LMV7291 is built with Texas Instruments'
advance submicron silicon-gate BiCMOS process. It
has bipolar inputs for improved noise performance
and CMOS outputs for rail-to-rail output swing.
APPLICATIONS
•
•
•
•
Mobile Communications
Laptops and PDA's
Battery Powered Electronics
General Purpose Low Voltage Applications
Typical Circuit
VIN
VCC
R1
C1 =
0.1µF
C2 =
10µF
+
VOUT
R2
-
VREF
Figure 1. Threshold Detector
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2004–2013, Texas Instruments Incorporated
LMV7291
SNOSA86E – FEBRUARY 2004 – REVISED MARCH 2013
Absolute Maximum Ratings
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(1) (2)
ESD Tolerance
VIN Differential
2KV
(3)
200V
(4)
±Supply Voltage
Supply Voltage (V+ - V−)
5.5V
V+ +0.1V, V− −0.1V
Voltage at Input/Output pins
Soldering Information
Infrared or Convection (20 sec.)
235°C
Wave Soldering (10 sec.)
260°C
−65°C to +150°C
Storage Temperature Range
Junction Temperature
(1)
(2)
(3)
(4)
(5)
(5)
+150°C
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 ensured. For ensured specifications and the test
conditions, see the Electrical Characteristics.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
Human body model, 1.5kΩ in series with 100pF.
Machine Model, 0Ω in series with 200pF.
Typical values represent the most likely parametric norm.
Operating Ratings
(1)
Operating Temperature Range
Package Thermal Resistance
(2)
−40°C to +85°C
(2)
SC70
(1)
(2)
2
265°C/W
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 ensured. For ensured specifications and the test
conditions, see the Electrical Characteristics.
The maximum power dissipation is a function of TJ(MAX), θJA, and TA. The maximum allowable power dissipation at any ambient
temperature is PD = (TJ(MAX) - TA)/θJA. All numbers apply for packages soldered directly into a PC board.
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SNOSA86E – FEBRUARY 2004 – REVISED MARCH 2013
1.8V Electrical Characteristics
Unless otherwise specified, all limits ensured for TJ = 25°C, V+ = 1.8V, V− = 0V. Boldface limits apply at the temperature
extremes. (1)
Symbol
Parameter
Condition
Min (2)
Typ (3)
Max (2)
Units
0.3
4
6
mV
VOS
Input Offset Voltage
TC VOS
Input Offset Temperature Drift
10
uV/C
IB
Input Bias Current
10
nA
IOS
Input Offset Current
200
pA
IS
Supply Current
LMV7291
ISC
Output Short Circuit Current
Sourcing, VO = 0.9V
VCM = 0.9V
(4)
9
3.5
6
4
6
IO = 0.5mA
1.7
1.74
IO = 1.5mA
1.58
1.63
Sinking, VO = 0.9V
VOH
Output Voltage High
VOL
Output Voltage Low
VCM
Input Common Mode Voltage Range
12
14
mA
V
IO = −0.5mA
52
70
IO = −1.5mA
166
220
CMRR > 45 dB
µA
mV
1.9
V
−0.1
V
CMRR
Common Mode Rejection Ratio
0 < VCM < 1.8V
47
78
dB
PSRR
Power Supply Rejection Ratio
V+ = 1.8V to 5V
55
80
dB
ILEAKAGE
Output Leakage Current
VO = 1.8V
2
pA
(1)
(2)
(3)
(4)
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No ensured specification of parametric performance is indicated in the electrical
tables under conditions of internal self heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
All limits are specified by testing or statistical analysis.
Typical values represent the most likely parametric norm.
Offset Voltage average drift determined by dividing the change in VOS at temperature extremes into the total temperature change.
1.8V AC Electrical Characteristics
Unless otherwise specified, all limits ensured for TJ = 25°C, V+ = 1.8V, V− = 0V, VCM = 0.5V, VO = V+/2 and RL > 1MΩ to V−.
Boldface limits apply at the temperature extremes. (1)
Symbol
tPHL
tPLH
(1)
(2)
(3)
Parameter
Propagation Delay
(High to Low)
Propagation Delay
(Low to High)
Condition
Min (2)
Typ (3)
Max (2)
Units
Input Overdrive = 20mV
Load = 50pF//5kΩ
880
ns
Input Overdrive = 50mV
Load = 50pF//5kΩ
570
ns
Input Overdrive = 20mV
Load = 50pF//5kΩ
1100
ns
Input Overdrive = 50mV
Load = 50pF//5kΩ
800
ns
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No ensured specification of parametric performance is indicated in the electrical
tables under conditions of internal self heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
All limits are specified by testing or statistical analysis.
Typical values represent the most likely parametric norm.
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2.7V Electrical Characteristics
Unless otherwise specified, all limits ensured for TJ = 25°C, V+ = 2.7V, V− = 0V. Boldface limits apply at the temperature
extremes. (1)
Symbol
Parameter
Conditions
Min (2)
Typ (3)
Max (2)
Units
0.3
4
6
mV
VOS
Input Offset Voltage
TC VOS
Input Offset Temperature Drift
10
µV/C
IB
Input Bias Current
10
nA
IOS
Input offset Current
200
pA
IS
Supply Current
LMV7291
ISC
Output Short Circuit Current
Sourcing, VO = 1.35V
12
15
Sinking, VO = 1.35V
12
15
IO = 0.5mA
2.63
2.66
IO = 2.0mA
2.48
2.55
VOH
Output Voltage High
VOL
Output Voltage Low
VCM
Input Common Voltage Range
VCM = 1.35V
(4)
9
13
15
mA
V
IO = −0.5mA
50
70
IO = −2mA
155
220
CMRR > 45dB
µA
2.8
−0.1
mV
V
V
CMRR
Common Mode Rejection Ratio
0 < VCM < 2.7V
47
78
dB
PSRR
Power Supply Rejection Ratio
V+ = 1.8V to 5V
55
80
dB
ILEAKAGE
Output Leakage Current
VO = 2.7V
2
pA
(1)
(2)
(3)
(4)
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No ensured specification of parametric performance is indicated in the electrical
tables under conditions of internal self heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
All limits are specified by testing or statistical analysis.
Typical values represent the most likely parametric norm.
Offset Voltage average drift determined by dividing the change in VOS at temperature extremes into the total temperature change.
2.7V AC Electrical Characteristics
Unless otherwise specified, all limits ensured for TJ = 25°C, V+ = 2.7V, V− = 0V, VCM = 0.5V, VO = V+/2 and RL > 1MΩ to V−.
Boldface limits apply at the temperature extremes. (1)
Symbol
tPHL
tPLH
(1)
(2)
(3)
4
Parameter
Propagation Delay
(High to Low)
Propagation Delay
(Low to High)
Condition
Min (2)
Typ (3)
Max (2)
Units
Input Overdrive = 20mV
Load = 50pF//5kΩ
1200
ns
Input Overdrive = 50mV
Load = 50pF//5kΩ
810
ns
Input Overdrive = 20mV
Load = 50pF//5kΩ
1300
ns
Input Overdrive = 50mV
Load = 50pF//5kΩ
860
ns
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No ensured specification of parametric performance is indicated in the electrical
tables under conditions of internal self heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
All limits are specified by testing or statistical analysis.
Typical values represent the most likely parametric norm.
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5V Electrical Characteristics
Unless otherwise specified, all limits ensured for TJ = 25°C, V+ = 5V, V− = 0V. Boldface limits apply at the temperature
extremes. (1)
Symbol
Parameter
Conditions
Min (2)
Typ (3)
Max (2)
Units
0.3
4
6
mV
VOS
Input Offset Voltage
TC VOS
Input Offset Temperature Drift
10
µV/C
IB
Input Bias Current
10
nA
IOS
Input Offset Current
200
pA
IS
Supply Current
LMV7291
ISC
Output Short Circuit Current
Sourcing, VO = 2.5V
28
34
Sinking, VO = 2.5V
28
34
IO = 0.5mA
4.93
4.96
IO = 4.0mA
4.70
4.77
VOH
Output Voltage High
VOL
Output Voltage Low
VCM
Input Common Voltage Range
VCM = 2.5V
(4)
10
14
16
mA
V
IO = −0.5mA
27
70
IO = −4.0mA
225
300
CMRR > 45dB
µA
mV
5.1
V
−0.1
CMRR
Common Mode Rejection Ratio
0 < VCM < 5.0V
47
78
dB
PSRR
Power Supply Rejection Ratio
V+ = 1.8V to 5V
55
80
dB
ILEAKAGE
Output Leakage Current
VO = 5V
2
pA
(1)
(2)
(3)
(4)
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No ensured specification of parametric performance is indicated in the electrical
tables under conditions of internal self heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
All limits are specified by testing or statistical analysis.
Typical values represent the most likely parametric norm.
Offset Voltage average drift determined by dividing the change in VOS at temperature extremes into the total temperature change.
5.0V AC Electrical Characteristics
Unless otherwise specified, all limits ensured for TJ = 25°C, V+ = 5.0V, V− = 0V, VCM = 0.5V, VO = V+/2 and RL > 1MΩ to V−.
Boldface limits apply at the temperature extremes. (1)
Symbol
tPHL
tPLH
(1)
(2)
(3)
Parameter
Propagation Delay
(High to Low)
Propagation Delay
(Low to High)
Condition
Min (2)
Typ (3)
Max (2)
Units
Input Overdrive = 20mV
Load = 50pF//5kΩ
2100
ns
Input Overdrive = 50mV
Load = 50pF//5kΩ
1380
ns
Input Overdrive = 20mV
Load = 50pF//5kΩ
1800
ns
Input Overdrive = 50mV
Load = 50pF//5kΩ
1100
ns
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No ensured specification of parametric performance is indicated in the electrical
tables under conditions of internal self heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
All limits are specified by testing or statistical analysis.
Typical values represent the most likely parametric norm.
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Connection Diagram
1
5
VOUT
+
V
2
GND
3
4
+IN
-IN
Figure 2. 5-Pin SC70 – Top View
See Package Number DCK
6
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SNOSA86E – FEBRUARY 2004 – REVISED MARCH 2013
Typical Performance Characteristics
(TA = 25°C, Unless otherwise specified).
VOS
vs.
VCM
VOS
vs.
VCM
VSUPPLY = ±0.9V
800
800
VSUPPLY = ±1.35V
-40°C
-40°C
400
400
VOS (PV)
VOS (PV)
25°C
0
0
85°C
-400
-400
25°C
85°C
-800
-800
-0.9 -0.7 -0.5 -0.3 -0.1 0.1 0.3 0.5 0.7 0.9
0
0.45
VOS
vs.
VCM
Short Circuit
vs.
Supply Voltage
SHORT CIRCUIT OUTPUT CURRENT (mA)
Figure 4.
-40°C
VOS (PV)
-0.45
Figure 3.
400
0
-400
25°C
85°C
-800
-2.5 -2
-0.9
VCM (V)
VSUPPLY = ±2.5V
800
-1.35
VCM (V)
-1
0
1
2 2.5
0.9
1.35
40
SOURCE
30
20
SINK
10
0
1.8
2.44
VCM (V)
3.08
3.72
4.36
5.0
SUPPLY VOLTAGE (V)
Figure 5.
Figure 6.
Supply Current
vs.
Supply Voltage
Supply Current
vs.
Supply Voltage
25
10
SUPPLY CURRENT (PA)
SUPPLY CURRENT (PA)
85°C
9
85°C
85°C
8
25°C
7
6
20
15
25°C
10
-40°C
5
-40°C
VOUT = HIGH
0
5
1.8
2.44
3.08
3.72
4.36
5.0
1.5
2
2.5
3
3.5
4
4.5
5
VSUPPLY (V)
SUPPLY VOLTAGE (V)
Figure 7.
Figure 8.
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Typical Performance Characteristics (continued)
(TA = 25°C, Unless otherwise specified).
Supply Current
vs.
Supply Voltage
Output Positive Swing
vs.
VSUPPLY
600
25
500
V - VOUT (mV)
15
10
25°C
+
SUPPLY CURRENT (PA)
ISOURCE
85°C
20
-40°C
400
4mA
300
2mA
200
1.5mA
5
100
0.5mA
VOUT = LOW
0
0
1.5
2
2.5
3
3.5
4
1.8
5
4.5
2.3
2.8
3.3
3.8
4.3
4.8
VSUPPLY (V)
VSUPPLY (V)
Figure 9.
Figure 10.
Output Negative Swing
vs.
VSUPPLY
Output Positive Swing
vs.
ISOURCE
600
0.8
VSUPPLY = 1.8V
ISINK
0.7
500
85°C
V - VOUT (V)
400
4mA
-
VOUT - V (mV)
0.6
300
+
2mA
200
0.5
25°C
0.4
0.3
1.5mA
0.2
-40°C
100
0.1
0.5mA
0
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
0
0.5
1
1.5
2
2.5
3
3.5
4
ISOURCE (mA)
VSUPPLY (V)
Figure 11.
Figure 12.
Output Negative Swing
vs.
ISINK
Output Positive Swing
vs.
ISOURCE
0.5
0.8
VSUPPLY = 1.8V
VSUPPLY = 2.7V
0.45
0.7
85°C
85°C
0.4
0.6
V - VOUT (V)
-
VOUT - V (V)
0.35
0.5
25°C
+
0.4
0.3
25°C
0.3
0.25
0.2
0.15
0.2
-40°
0.1
-40°C
0.1
0.05
0
0
0
0.5
1
1.5
2
2.5
3
3.5
4
ISINK (mA)
0.5
1
1.5
2
2.5
3
3.5
4
ISOURCE (mA)
Figure 13.
8
0
Figure 14.
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Typical Performance Characteristics (continued)
(TA = 25°C, Unless otherwise specified).
Output Negative Swing
vs.
ISINK
Output Negative Swing
vs.
ISINK
0.5
0.4
VSUPPLY = 2.7V
0.45
VSUPPLY = 5V
85°C
85°C
0.4
25°C
-
0.3
VOUT - V (V)
-
VOUT - V (V)
0.3
0.35
25°C
0.25
0.2
0.2
0.15
0.1
0.1
-40°C
-40°C
0.05
0
0
0
0.5
1
1.5
2
2.5
3
3.5
4
0
0.5
1
1.5
Figure 15.
OUTPUT VOLTAGE
(V)
VSUPPLY = 5V
85°C
3.5
4
25°C
5
VCC = 1.8V
TEMP = 25°C
LOAD = 5k: 50pF
4
3
50mV
20mV
2
1
0
0.2
|
INPUT VOLTAGE
(mV)
+
V - VOUT (V)
0.3
0.1
-40°C
0
0
0.5
1
1.5
2
2.5
3
3.5
|
100
0
OVERDRIVE
-100
4
0
500
1000
Figure 17.
Propagation Delay (tPHL)
Propagation Delay (tPLH)
OUTPUT VOLTAGE
(V)
VCC = 1.8 V
4 TEMP = 25°C
3 LOAD = 5k: 50pF
50mV
1
2500 3000
Figure 18.
5
2
1500 2000
TIME (ns)
ISOURCE (mA)
OUTPUT VOLTAGE
(V)
3
Propagation Delay (tPLH)
0.4
20mV
5
VCC = 2.7V
TEMP = 25°C
LOAD = 5k: 50pF
4
3
2
1
50mV
20mV
0
|
|
100
OVERDRIVE
0
-100
500
1000
1500
INPUT VOLTAGE
(mV)
0
INPUT VOLTAGE
(mV)
2.5
Figure 16.
Output Positive Swing
vs.
ISOURCE
0
2
ISINK (mA)
ISINK (mA)
2000 2500 3000
|
|
100
0
OVERDRIVE
-100
0
500
1000
1500 2000 2500 3000
TIME (ns)
TIME (ns)
Figure 19.
Figure 20.
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Typical Performance Characteristics (continued)
(TA = 25°C, Unless otherwise specified).
Propagation Delay (tPLH)
VCC = 2.7 V
TEMP = 25°C
LOAD = 5k: 50pF
4
3
2
50mV
1
5
OUTPUT VOLTAGE
(V)
OUTPUT VOLTAGE
(V)
Propagation Delay (tPHL)
5
20mV
VCC = 5.0V
TEMP = 25°C
3 LOAD = 5k: 50pF
20mV
2
1
0
|
|
100
INPUT VOLTAGE
(mV)
INPUT VOLTAGE
(mV)
0
OVERDRIVE
0
-100
0
500
1000 1500
|
|
100
0
OVERDRIVE
-100
2000 2500 3000
0
500
1000 1500 2000
2500 3000
TIME (ns)
Figure 21.
Figure 22.
Propagation Delay (tPHL)
tPHL
vs.
Overdrive
5
8
VCC = 5.0 V
TEMP = 25°C
3 LOAD = 5k: 50pF
7
4
VS = 5V
6
2
50mV
1
0
tPHL (PS)
OUTPUT VOLTAGE
(V)
TIME (ns)
INPUT VOLTAGE
(mV)
50mV
4
20mV
|
|
100
OVERDRIVE
5
4
VS = 2.7V
3
2
0
1
-100
VS = 1.8V
0
0
500
1000 1500
2000 2500 3000
0
TIME (ns)
10
100
1000
OVERDRIVE (mV)
Figure 23.
Figure 24.
tPLH
vs.
Overdrive
5
VS = 5V
4.5
4
tPLH (PS)
3.5
3
2.5
VS = 2.7V
2
1.5
1
VS = 1.8V
0.5
0
1
10
100
1000
OVERDRIVE (mV)
Figure 25.
10
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APPLICATION NOTES
BASIC COMPARATOR
A comparator is often used to convert an analog signal to a digital signal. As shown in Figure 26, the comparator
compares an input voltage (VIN) to a reference voltage (VREF). If VIN is less than VREF, the output (VO) is low.
However, if VIN is greater than VREF, the output voltage (VO) is high.
V
VREF
+
VOLTS
VO
VO
VIN
+
VREF
V
-
TIME
VIN
Figure 26. LMV7291 Basic Comparator
RAIL-TO-RAIL INPUT STAGE
The LMV7291 has an input common mode voltage range (VCM) of −0.1V below the V− to 0.1V above V+. This is
achieved by using paralleled PNP and NPN differential input pairs. When the VCM is near V+, the NPN pair is on
and the PNP pair is off. When the VCM is near V−, the NPN pair is off and the PNP pair is on. The crossover point
between the NPN and PNP input stages is around 950mV from V+. Since each input stage has its own offset
voltage (VOS), the VOS of the comparator becomes a function of the VCM. See Figure 3, Figure 4, and Figure 5 in
Typical Performance Characteristics. In application design, it is recommended to keep the VCM away from the
crossover point to avoid problems. The wide input voltage range makes LMV7291 ideal in power supply
monitoring circuits, where the comparators are used to sense signals close to gnd and power supplies.
OUTPUT STAGE
The LMV7291 has a push-pull output stage. This output stage keeps the total system power consumption to the
absolute minimum. The only current consumed is the low supply current and the current going directly into the
load. When output switches, both PMOS and NMOS at the output stage are on at the same time for a very short
time. This allows current to flow directly between V+ and V− through output transistors. The result is a short spike
of current (shoot-through current) drawn from the supply and glitches in the supply voltages. The glitches can
spread to other parts of the board as noise. To prevent the glitches in supply lines, power supply bypass
capacitors must be installed. See CIRCUIT TECHNIQUES FOR AVOIDING OSCILLATIONS IN COMPARATOR
APPLICATIONS for details.
HYSTERESIS
It is a standard procedure to use hysteresis (positive feedback) around a comparator, to prevent oscillation, and
to avoid excessive noise on the output because the comparator is a good amplifier of its own noise.
Inverting Comparator with Hysteresis
The inverting comparator with hysteresis requires a three resistor network that are referenced to the supply
voltage VCC of the comparator (Figure 27). When VIN at the inverting input is less than VA, the voltage at the noninverting node of the comparator (VIN < VA), the output voltage is high (for simplicity assume VO switches as high
as VCC). The three network resistors can be represented as R1||R3 in series with R2. The lower input trip voltage
VA1 is defined as
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VA1 =
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VCC R2
(R1||R3) + R2
(1)
When VIN is greater than VA (VIN > VA), the output voltage is low and very close to ground. In this case the three
network resistors can be presented as R2//R3 in series with R1. The upper trip voltage VA2 is defined as
VA2 =
VCC (R2||R3)
R1 + (R2||R3)
(2)
The total hysteresis provided by the network is defined as
ΔVA = VA1 - VA2
(3)
A good typical value of ΔVA would be in the range of 5 to 50 mV. This is easily obtained by choosing R3 as 1000
to 100 times (R1||R2) for 5V operation, or as 300 to 30 times (R1||R2) for 1.8V operation.
Figure 27. Inverting Comparator with Hysteresis
Non-Inverting Comparator with Hysteresis
A non-inverting comparator with hysteresis requires a two resistor network, and a voltage reference (VREF) at the
inverting input (Figure 28). When VIN is low, the output is also low. For the output to switch from low to high, VIN
must rise up to VIN1, where VIN1 is calculated by
(4)
12
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When VIN is high, the output is also high. To make the comparator switch back to its low state, VIN must equal
VREF before VA will again equal VREF. VIN can be calculated by:
(5)
The hysteresis of this circuit is the difference between VIN1 and VIN2.
ΔVIN = VCCR1/R2
(6)
Figure 28. Non-Inverting Comparator with Hysteresis
CIRCUIT TECHNIQUES FOR AVOIDING OSCILLATIONS IN COMPARATOR APPLICATIONS
Feedback to almost any pin of a comparator can result in oscillation. In addition, when the input signal is a slow
voltage ramp or sine wave, the comparator may also burst into oscillation near the crossing point. To avoid
oscillation or instability, PCB layout should be engineered thoughtfully. Several precautions are recommended:
1. Power supply bypassing is critical, and will improve stability and transient response. Resistance and
inductance from power supply wires and board traces increase power supply line impedance. When supply
current changes, the power supply line will move due to its impedance. Large enough supply line shift will
cause the comparator to mis-operate. To avoid problems, a small bypass capacitor, such as 0.1uF ceramic,
should be placed immediately adjacent to the supply pins. An additional 6.8μF or greater tantalum capacitor
should be placed at the point where the power supply for the comparator is introduced onto the board. These
capacitors act as an energy reservoir and keep the supply impedance low. In dual supply application, a
0.1μF capacitor is recommended to be placed across V+ and V− pins.
2. Keep all leads short to reduce stray capacitance and lead inductance. It will also minimize any unwanted
coupling from any high-level signals (such as the output). The comparators can easily oscillate if the output
lead is inadvertently allowed to capacitively couple to the inputs via stray capacitance. This shows up only
during the output voltage transition intervals as the comparator changes states. Try to avoid a long loop
which could act as an inductor (coil).
3. It is a good practice to use an unbroken ground plane on a printed circuit board to provide all components
with a low inductive ground connection. Make sure ground paths are low-impedance where heavier currents
are flowing to avoid ground level shift. Preferably there should be a ground plane under the component.
4. The output trace should be routed away from inputs. The ground plane should extend between the output
and inputs to act as a guard.
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5. When the signal source is applied through a resistive network to one input of the comparator, it is usually
advantageous to connect the other input with a resistor with the same value, for both DC and AC
consideration. Input traces should be laid out symmetrically if possible.
6. All pins of any unused comparators should be tied to the negative supply.
Typical Applications
POSITIVE PEAK DETECTOR
A positive peak detect circuit is basically a comparator operated in a unity gain follower configuration, with a
capacitor as a load to maintain the highest voltage. A diode is added at the output to prevent the capacitor from
discharging through the output, and a 1MΩ resistor added in parallel to the capacitor to provide a high
impedance discharge path. When the input VIN increases, the inverting input of the comparator follows it, thus
charging the capacitor. When it decreases, the cap discharges through the 1MΩ resistor. The decay time can be
modified by changing the resistor. The output should be accessed through a follower circuit to prevent loading.
+VCC
VIN
+
-
VOUT
C1
10 PF
+
R2
1 M:
Figure 29. Positive Peak Detector
NEGATIVE PEAK DETECTOR
For the negative detector, the output transistor of the comparator acts as a low impedance current sink. Since
there is no pull-up resistor, the only discharge path will be the 1MΩ resistor and any load impedance used.
Decay time is changed by varying the 1MΩ resistor.
+VCC
VIN
+
VOUT
-
R1
1M:
+
C1
10PF
-VCC
Figure 30. Negative Peak Detector
SQUARE WAVE GENERATOR
A typical application for a comparator is as a square wave oscillator. The circuit below generates a square wave
whose period is set by the RC time constant of the capacitor C1and resistor R4. The maximum frequency is
limited by the large signal propagation delay of the comparator, and by the capacitive loading at the output,
which limits the output slew rate.
14
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SNOSA86E – FEBRUARY 2004 – REVISED MARCH 2013
R4 = 100 k:
C1 = 750 pF
VC
VO
+
R1 = 100 k:
V
+
VA
R3 = 100 k:
+
R2 = 100 k:
V
0
f | 10 kHz
Figure 31. Squarewave Oscillator
To analyze the circuit, consider it when the output is high. That implies that the inverted input (VC) is lower than
the non-inverting input (VA). This causes the C1 to get charged through R4, and the voltage VC increases till it is
equal to the non-inverting input. The value of VA at this point is
VCC.R2
VA1 =
R2 + R1||R3
(7)
If R1 = R2 = R3 then VA1 = 2VCC/3
At this point the comparator switches pulling down the output to the negative rail. The value of VA at this point is
VCC (R2||R3)
VA2 =
R1 + (R2||R3)
(8)
If R1 = R2 = R3 then VA2 = VCC/3
The capacitor C1 now discharges through R4, and the voltage VC decreases till it is equal to VA2, at which point
the comparator switches again, bringing it back to the initial stage. The time period is equal to twice the time it
takes to discharge C1 from 2VCC/3 to VCC/3, which is given by R4C1.ln2. Hence the formula for the frequency is:
F = 1/(2.R4.C1.ln2)
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REVISION HISTORY
Changes from Revision D (March 2013) to Revision E
•
16
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 15
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PACKAGE OPTION ADDENDUM
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30-Sep-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LMV7291MG
ACTIVE
SC70
DCK
5
1000
Non-RoHS
& Green
Call TI
Level-1-260C-UNLIM
-40 to 85
C36
LMV7291MG/NOPB
ACTIVE
SC70
DCK
5
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
C36
LMV7291MGX/NOPB
ACTIVE
SC70
DCK
5
3000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
C36
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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