Product
Folder
Sample &
Buy
Technical
Documents
Tools &
Software
Support &
Community
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
LMx31x Precision Voltage-to-Frequency Converters
1 Features 3 Description
The LMx31 family of voltage-to-frequency converters
1• Ensured Linearity 0.01% Maximum are ideally suited for use in simple low-cost circuits
• Improved Performance in Existing Voltage-to- for analog-to-digital conversion, precision frequency-
Frequency Conversion Applications to-voltage conversion, long-term integration, linear
• Split or Single-Supply Operation frequency modulation or demodulation, and many
other functions. The output when used as a voltage-
• Operates on Single 5-V Supply to-frequency converter is a pulse train at a frequency
• Pulse Output Compatible With All Logic Forms precisely proportional to the applied input voltage.
• Excellent Temperature Stability: ±50 ppm/°C Thus, it provides all the inherent advantages of the
Maximum voltage-to-frequency conversion techniques, and is
easy to apply in all standard voltage-to-frequency
• Low Power Consumption: 15 mW Typical at 5 V converter applications.
• Wide Dynamic Range, 100 dB Minimum at 10-kHz
Full Scale Frequency Device Information(1)
• Wide Range of Full Scale Frequency: PART NUMBER PACKAGE BODY SIZE (NOM)
1 Hz to 100 kHz LM231 PDIP (8) 9.81 mm × 6.35 mm
• Low-Cost LM331
(1) For all available packages, see the orderable addendum at
2 Applications the end of the data sheet.
• Voltage to Frequency Conversions
• Frequency to Voltage Conversions
• Remote-Sensor Monitoring
• Tachometers
Schematic Diagram
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
www.ti.com
Table of Contents
8.3 Feature Description................................................. 10
1 Features.................................................................. 18.4 Device Functional Modes........................................ 10
2 Applications ........................................................... 19 Application and Implementation ........................ 11
3 Description............................................................. 19.1 Application Information............................................ 11
4 Revision History..................................................... 29.2 Typical Applications ................................................ 12
5 Description continued........................................... 39.3 System Examples .................................................. 15
6 Pin Configuration and Functions......................... 410 Power Supply Recommendations ..................... 18
7 Specifications......................................................... 411 Layout................................................................... 18
7.1 Absolute Maximum Ratings ...................................... 411.1 Layout Guidelines ................................................. 18
7.2 ESD Ratings.............................................................. 411.2 Layout Example .................................................... 18
7.3 Recommended Operating Conditions....................... 512 Device and Documentation Support................. 19
7.4 Thermal Information.................................................. 512.1 Related Links ........................................................ 19
7.5 Electrical Characteristics........................................... 512.2 Community Resources.......................................... 19
7.6 Dissipation Ratings ................................................... 612.3 Trademarks........................................................... 19
7.7 Typical Characteristics.............................................. 712.4 Electrostatic Discharge Caution............................ 19
8 Detailed Description.............................................. 912.5 Glossary................................................................ 19
8.1 Overview................................................................... 913 Mechanical, Packaging, and Orderable
8.2 Functional Block Diagram......................................... 9Information........................................................... 19
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision B (March 2013) to Revision C Page
• Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional
Modes,Application and Implementation section, Power Supply Recommendations section, Layout section, Device
and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .............................. 1
Changes from Revision A (March 2013) to Revision B Page
• Changed layout of National Data Sheet to TI format ............................................................................................................. 1
2Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated
Product Folder Links: LM231 LM331
LM231
,
LM331
www.ti.com
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
5 Description continued
Further, the LMx31A attain a new high level of accuracy versus temperature which could only be attained with
expensive voltage-to-frequency modules. Additionally the LMx31 are ideally suited for use in digital systems at
low power supply voltages and can provide low-cost analog-to-digital conversion in microprocessor-controlled
systems. And, the frequency from a battery-powered voltage-to-frequency converter can be easily channeled
through a simple photo isolator to provide isolation against high common-mode levels.
The LMx31 uses a new temperature-compensated band-gap reference circuit, to provide excellent accuracy over
the full operating temperature range, at power supplies as low as 4 V. The precision timer circuit has low bias
currents without degrading the quick response necessary for 100-kHz voltage-to-frequency conversion. And the
output are capable of driving 3 TTL loads, or a high-voltage output up to 40 V, yet is short-circuit-proof against
VCC.
Copyright © 1999–2015, Texas Instruments Incorporated Submit Documentation Feedback 3
Product Folder Links: LM231 LM331
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
www.ti.com
6 Pin Configuration and Functions
P Package
8-Pin PDIP
Top View
Pin Functions
PIN I/O DESCRIPTION
NAME NO.
IOUT 1 O Current Output
IREF 2 I Reference Current
FOUT 3 O Frequency Output. This output is an open-collector output and requires a pullup resistor.
GND 4 G Ground
RC 5 I R-C filter input
THRESH 6 I Threshold input
COMPIN 7 I Comparator Input
VS 8 P Supply Voltage
7 Specifications
7.1 Absolute Maximum Ratings(1)(2)(3)
MIN MAX UNIT
Supply Voltage, VS40 V
Output Short Circuit to Ground Continuous
Output Short Circuit to VCC Continuous
Input Voltage −0.2 +VSV
Lead Temperature (Soldering, 10 sec.) PDIP 260 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) All voltages are measured with respect to GND = 0 V, unless otherwise noted.
(3) If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications.
7.2 ESD Ratings VALUE UNIT
V(ESD) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001(1)(2) ±500 V
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) Human body model, 100 pF discharged through a 1.5-kΩresistor.
4Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated
Product Folder Links: LM231 LM331
LM231
,
LM331
www.ti.com
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
7.3 Recommended Operating Conditions MIN MAX UNIT
LM231, LM231A −25 85 °C
Operating Ambient
Temperature LM331, LM331A 0 70 °C
Supply Voltage, VS(1) 4 40 V
(1) All voltages are measured with respect to GND = 0 V, unless otherwise noted.
7.4 Thermal Information LM312, LM331
THERMAL METRIC(1) P (PDIP) UNIT
8 PINS
RθJA Junction-to-ambient thermal resistance 100 °C/W
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
7.5 Electrical Characteristics
All specifications apply in the circuit of Figure 16, with 4.0 V ≤VS≤40 V, TA= 25°C, unless otherwise specified.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
% Full-
4.5 V ≤VS≤20 V ±0.003 ±0.01 Scale
VFC Non-Linearity (1) % Full-
TMIN ≤TA≤TMAX ±0.006 ±0.02 Scale
%Full-
VFC Non-Linearity in Circuit of Figure 14 VS= 15 V, f = 10 Hz to 11 kHz ±0.024 ±0.14 Scale
LM231, LM231A VIN =−10 V, RS= 14 kΩ0.95 1 1.05 kHz/V
Conversion Accuracy
Scale Factor (Gain) LM331, LM331A 0.9 1 1.1 kHz/V
TMIN ≤TA≤TMAX
LMx31 ±30 ±150 ppm/°C
Temperature Stability 4.5 V ≤VS≤20 V
of Gain LMx31A ±20 ±50 ppm/°C
4.5 V ≤VS≤10 V 0.01 0.1 %/V
Change of Gain with VS10 V ≤VS≤40 V 0.006 0.06 %/V
Rated Full-Scale Frequency VIN =−10 V 10.0 kHz
% Full-
Gain Stability vs. Time (1000 Hours) TMIN ≤TA≤TMAX ±0.02 Scale
Over Range (Beyond Full-Scale) Frequency VIN =−11 V 10%
INPUT COMPARATOR
Offset Voltage ±3 ±10 mV
LM231/LM331 TMIN ≤TA≤TMAX ±4 ±14 mV
LM231A/LM331A TMIN ≤TA≤TMAX ±3 ±10 mV
Bias Current −80 −300 nA
Offset Current ±8 ±100 nA
Common-Mode Range TMIN ≤TA≤TMAX −0.2 VCC −2 V
TIMER
Timer Threshold Voltage, Pin 5 0.63 × VS0.667 × VS0.7 × VS
Input Bias Current, Pin 5 VS= 15 V
All Devices 0V ≤VPIN 5 ≤9.9 V ±10 ±100 nA
LM231/LM331 VPIN 5 = 10 V 200 1000 nA
LM231A/LM331A VPIN 5 = 10 V 200 500 nA
VSAT PIN 5 (Reset) I = 5 mA 0.22 0.5 V
(1) Non-linearity is defined as the deviation of fOUT from VIN × (10 kHz/−10 VDC) when the circuit has been trimmed for zero error at 10 Hz
and at 10 kHz, over the frequency range 1 Hz to 11 kHz. For the timing capacitor, CT, use NPO ceramic, Teflon®, or polystyrene.
Copyright © 1999–2015, Texas Instruments Incorporated Submit Documentation Feedback 5
Product Folder Links: LM231 LM331
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
www.ti.com
Electrical Characteristics (continued)
All specifications apply in the circuit of Figure 16, with 4.0 V ≤VS≤40 V, TA= 25°C, unless otherwise specified.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
CURRENT SOURCE (PIN 1)
LM231, LM231A RS= 14 kΩ, VPIN 1 = 0 126 135 144 μA
Output Current LM331, LM331A 116 136 156 μA
Change with Voltage 0V ≤VPIN 1 ≤10 V 0.2 1 μA
LM231, LM231A, 0.02 10 nA
Current Source OFF LM331, LM331A
Leakage All Devices TA= TMAX 2 50 nA
Operating Range of Current (Typical) (10 to 500) μA
REFERENCE VOLTAGE (PIN 2)
LM231, LM231A 1.76 1.89 2.02 VDC
LM331, LM331A 1.7 1.89 2.08 VDC
Stability vs. Temperature ±60 ppm/°C
Stability vs. Time, 1000 Hours ±0.1%
LOGIC OUTPUT (PIN 3)
I = 5 mA 0.15 0.5 V
VSAT I = 3.2 mA (2 TTL Loads), 0.1 0.4 V
TMIN ≤TA≤TMAX
OFF Leakage ±0.05 1 μA
SUPPLY CURRENT
VS= 5 V 2 3 4 mA
LM231, LM231A VS= 40 V 2.5 4 6 mA
VS= 5 V 1.5 3 6 mA
LM331, LM331A VS= 40 V 2 4 8 mA
7.6 Dissipation Ratings VALUE UNIT
Package Dissipation at 25°C(1) 1.25 W
(1) The absolute maximum junction temperature (TJmax) for this device is 150°C. The maximum allowable power dissipation is dictated by
TJmax, the junction-to-ambient thermal resistance (θJA), and the ambient temperature TA, and can be calculated using the formula
PDmax = (TJmax - TA) / θJA. The values for maximum power dissipation will be reached only when the device is operated in a severe
fault condition (e.g., when input or output pins are driven beyond the power supply voltages, or the power supply polarity is reversed).
Obviously, such conditions should always be avoided.
6Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated
Product Folder Links: LM231 LM331
LM231
,
LM331
www.ti.com
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
7.7 Typical Characteristics
(All electrical characteristics apply for the circuit of Figure 16, unless otherwise noted.)
Figure 1. Non-Linearity Error as Precision V-to-F Converter Figure 2. Non-Linearity Error
(Figure 16)
Figure 4. Frequency vs. Temperature
Figure 3. Non-Linearity Error vs. Power Supply Voltage
Figure 6. Output Frequency vs. VSUPPLY
Figure 5. VREF vs. Temperature
Copyright © 1999–2015, Texas Instruments Incorporated Submit Documentation Feedback 7
Product Folder Links: LM231 LM331
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
www.ti.com
Typical Characteristics (continued)
(All electrical characteristics apply for the circuit of Figure 16, unless otherwise noted.)
Figure 8. Non-Linearity Error (Figure 14)
Figure 7. 100 kHz Non-Linearity Error (Figure 17)
Figure 9. Input Current (Pins 6,7) vs. Temperature Figure 10. Power Drain vs. VSUPPLY
Figure 12. Non-Linearity Error, Precision F-to-V Converter
Figure 11. Output Saturation Voltage vs. IOUT (Pin 3) (Figure 19)
8Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated
Product Folder Links: LM231 LM331
LM231
,
LM331
www.ti.com
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
8 Detailed Description
8.1 Overview
8.1.1 Detail of Operation, Functional Block Diagram
The Functional Block Diagram shows a band gap reference which provides a stable 1.9-VDC output. This 1.9 VDC
is well regulated over a VSrange of 3.9 V to 40 V. It also has a flat, low temperature coefficient, and typically
changes less than ½% over a 100°C temperature change.
The current pump circuit forces the voltage at pin 2 to be at 1.9 V, and causes a current i = 1.90 V/RSto flow.
For RS=14 k, i=135 μA. The precision current reflector provides a current equal to i to the current switch. The
current switch switches the current to pin 1 or to ground, depending upon the state of the R-S flip-flop.
The timing function consists of an R-S flip-flop and a timer comparator connected to the external RtCtnetwork.
When the input comparator detects a voltage at pin 7 higher than pin 6, it sets the R-S flip-flop which turns ON
the current switch and the output driver transistor. When the voltage at pin 5 rises to ⅔VCC, the timer comparator
causes the R-S flip-flop to reset. The reset transistor is then turned ON and the current switch is turned OFF.
However, if the input comparator still detects the voltage on pin 7 as higher than pin 6 when pin 5 crosses ⅔
VCC, the flip-flop will not be reset, and the current at pin 1 will continue to flow, trying to make the voltage at pin 6
higher than pin 7. This condition will usually apply under start-up conditions or in the case of an overload voltage
at signal input. During this sort of overload the output frequency will be 0. As soon as the signal is restored to the
working range, the output frequency will be resumed.
8.2 Functional Block Diagram
Copyright © 1999–2015, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Links: LM231 LM331
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
www.ti.com
8.3 Feature Description
The LMx31 operate over a wide voltage range of 4 V to 40 V.
The voltage at pin 2 is regulated at 1.90 VDC for all values of i between 10 μA to 500 μA. It can be used as a
voltage reference for other components, but take care to ensure that current is not taken from it which could
reduce the accuracy of the converter.
8.4 Device Functional Modes
The output driver transistor acts to saturate pin 3 with an ON resistance of about 50 Ω. In case of overvoltage,
the output current is actively limited to less than 50 mA.
If the voltage on pin 7 is higher than pin 6 when pin 5 crosses ⅔VCC, the LMx31 internal flip-flop will not be
reset, and the current at pin 1 will continue to flow, trying to make the voltage at pin 6 higher than pin 7. This
condition will usually apply under start-up conditions or in the case of an overload voltage at signal input. During
this sort of overload the output frequency will be 0. As soon as the signal is restored to the working range, the
output frequency will be resumed.
10 Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated
Product Folder Links: LM231 LM331
LM231
,
LM331
www.ti.com
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
9.1.1 Simplified Voltage-to-Frequency Converter
The operation of these blocks is best understood by going through the operating cycle of the basic V-to-F
converter, Figure 13, which consists of the simplified block diagram of the LMx31 and the various resistors and
capacitors connected to it.
The voltage comparator compares a positive input voltage, V1, at pin 7 to the voltage, Vx, at pin 6. If V1 is
greater, the comparator will trigger the 1-shot timer. The output of the timer will turn ON both the frequency
output transistor and the switched current source for a period t = 1.1 RtCt. During this period, the current i will
flow out of the switched current source and provide a fixed amount of charge, Q = i × t, into the capacitor, CL.
This will normally charge Vxup to a higher level than V1. At the end of the timing period, the current i will turn
OFF, and the timer will reset itself.
Now there is no current flowing from pin 1, and the capacitor CLwill be gradually discharged by RLuntil Vxfalls
to the level of V1. Then the comparator will trigger the timer and start another cycle.
The current flowing into CLis exactly IAVE = i × (1.1×RtCt) × f, and the current flowing out of CLis exactly Vx/RL≃
VIN/RL. If VIN is doubled, the frequency will double to maintain this balance. Even a simple V-to-F converter can
provide a frequency precisely proportional to its input voltage over a wide range of frequencies.
9.1.2 Principles of Operation
The LMx31 are monolithic circuits designed for accuracy and versatile operation when applied as voltage-to-
frequency (V-to-F) converters or as frequency-to-voltage (F-to-V) converters. A simplified block diagram of the
LMx31 is shown in Figure 13 and consists of a switched current source, input comparator, and 1-shot timer.
Figure 13. Simplified Block Diagram of Stand-Alone
Voltage-to-Frequency Converter and
External Components
Copyright © 1999–2015, Texas Instruments Incorporated Submit Documentation Feedback 11
Product Folder Links: LM231 LM331
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
www.ti.com
9.2 Typical Applications
9.2.1 Basic Voltage-to-Frequency Converter
The simple stand-alone V-to-F converter shown in Figure 14 includes all the basic circuitry of Figure 13 plus a
few components for improved performance.
*Use stable components with low temperature coefficients. See Application Information.
**0.1 μF or 1 μF, See Typical Applications.
Figure 14. Simple Stand-Alone V-to-F Converter
with ±0.03% Typical Linearity (f = 10 Hz to 11 kHz)
9.2.1.1 Design Requirements
For this example, the system requirements are 0.05% linearity over an output frequency range of 10 Hz to 4 kHz
with an input voltage range of 25 mV to 12.5 V. The available supply voltage is 15.0 V.
9.2.1.2 Detailed Design Procedure
A capacitor CIN is added from pin 7 to ground to act as a filter for VIN, use of a 0.1 μF is appropriate for this
application. A value of 0.01 μF to 0.1 μF will be adequate in most cases; however, in cases where better filtering
is required, a 1-μF capacitor can be used. When the RC time constants are matched at pin 6 and pin 7, a voltage
step at VIN will cause a step change in fOUT. If CIN is much less than CL, a step at VIN may cause fOUT to stop
momentarily.
Next, we cancel the comparator bias current by setting RIN to 100 kΩto match RL. This will help to minimize any
frequency offset.
For best results, all the components should be stable low-temperature-coefficient components, such as metal-film
resistors. The capacitor should have low dielectric absorption; depending on the temperature characteristics
desired, NPO ceramic, polystyrene, Teflon or polypropylene are best suited.
The resistance RSat pin 2 is made up of a 12-kΩfixed resistor plus a 5-kΩ(cermet, preferably) gain adjust
rheostat. The function of this adjustment is to trim out the gain tolerance of the LMx31, and the tolerance of Rt,
RLand Ct.
12 Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated
Product Folder Links: LM231 LM331
LM231
,
LM331
www.ti.com
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
Typical Applications (continued)
A 47-Ωresistor in series with the 1-μF capacitor (CL) provides hysteresis, which helps the input comparator
provide the excellent linearity.
This results in the transfer function of ƒOUT = (VIN / 2.09 V) × (RS/ RL) × (1 / RtCt).
9.2.1.3 Application Curve
Figure 15. Output Non-Linearity Error vs. Frequency
Copyright © 1999–2015, Texas Instruments Incorporated Submit Documentation Feedback 13
Product Folder Links: LM231 LM331
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
www.ti.com
Typical Applications (continued)
9.2.2 Precision V-To-F Converter
In this circuit, integration is performed by using a conventional operational amplifier and feedback capacitor, CF.
When the integrator's output crosses the nominal threshold level at pin 6 of the LMx31, the timing cycle is
initiated.
The average current fed into the summing point of the op-amp (pin 2) is i × (1.1 RtCt) × f which is perfectly
balanced with −VIN/RIN. In this circuit, the voltage offset of the LMx31 input comparator does not affect the offset
or accuracy of the V-to-F converter as it does in the stand-alone V-to-F converter; nor does the LM231/331 bias
current or offset current. Instead, the offset voltage and offset current of the operational amplifier are the only
limits on how small the signal can be accurately converted. Since op-amps with voltage offset well below 1 mV
and offset currents well below 2 nA are available at low cost, this circuit is recommended for best accuracy for
small signals. This circuit also responds immediately to any change of input signal (which a stand-alone circuit
does not) so that the output frequency will be an accurate representation of VIN, as quickly as the spacing of the
2 output pulses can be measured.
In the precision mode, excellent linearity is obtained because the current source (pin 1) is always at ground
potential and that voltage does not vary with VIN or fOUT. (In the stand-alone V-to-F converter, a major cause of
non-linearity is the output impedance at pin 1 which causes i to change as a function of VIN).
The circuit of Figure 17 operates in the same way as Figure 16, but with the necessary changes for high-speed
operation.
*Use stable components with low temperature coefficients.
**This resistor can be 5 kΩor 10 kΩfor VS= 8 V to 22 V, but must be 10 kΩfor VS= 4.5 V to 8 V.
***Use low offset voltage and low offset current op-amps for A1: recommended type LF411A
Figure 16. Standard Test Circuit and Applications Circuit, Precision Voltage-to-Frequency Converter
14 Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated
Product Folder Links: LM231 LM331
LM231
,
LM331
www.ti.com
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
9.3 System Examples
9.3.1 F-to-V Converters
In these applications, a pulse input at fIN is differentiated by a C-R network and the negative-going edge at pin 6
causes the input comparator to trigger the timer circuit. Just as with a V-to-F converter, the average current
flowing out of pin 1 is IAVERAGE = i × (1.1 RtCt) × f.
In the simple circuit of Figure 18, this current is filtered in the network RL= 100 kΩand 1 μF. The ripple will be
less than 10-mV peak, but the response will be slow, with a 0.1 second time constant, and settling of 0.7 second
to 0.1% accuracy.
In the precision circuit, an operational amplifier provides a buffered output and also acts as a 2-pole filter. The
ripple will be less than 5-mV peak for all frequencies above 1 kHz, and the response time will be much quicker
than in Figure 18. However, for input frequencies below 200 Hz, this circuit will have worse ripple than Figure 18.
The engineering of the filter time-constants to get adequate response and small enough ripple simply requires a
study of the compromises to be made. Inherently, V-to-F converter response can be fast, but F-to-V response
can not.
10 kHz Full-Scale, ±0.06% Non-Linearity
*Use stable components with low temperature coefficients.
100 kHz Full-Scale, ±0.03% Non-Linearity
*Use stable components with low temperature coefficients.
**This resistor can be 5 kΩor 10 kΩfor VS=8V to 22V, but must be
10 kΩfor VS=4.5V to 8V.
***Use low offset voltage and low offset current op-amps for A1:
recommended types LF411A or LF356.
Figure 17. Precision Voltage-to-Frequency Figure 18. Simple Frequency-to-Voltage Converter
Converter
Copyright © 1999–2015, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Links: LM231 LM331
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
www.ti.com
System Examples (continued)
*L14F-1, L14G-1 or L14H-1, photo transistor (General Electric Co.)
or similar
10 kHz Full-Scale With 2-Pole Filter, ±0.01% Non-Linearity
Maximum
*Use stable components with low temperature coefficients.
Figure 19. Precision Frequency-to-Voltage Figure 20. Light Intensity to Frequency Converter
Converter,
Figure 21. Temperature to Frequency Converter Figure 22. Long-Term Digital Integrator Using VFC
Figure 23. Basic Analog-to-Digital Converter Using Figure 24. Analog-to-Digital Converter With
Microprocessor
Voltage-to-Frequency Converter
16 Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated
Product Folder Links: LM231 LM331
LM231
,
LM331
www.ti.com
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
System Examples (continued)
Figure 25. Remote Voltage-to-Frequency Converter Figure 26. Voltage-to-Frequency Converter With
With 2-Wire Transmitter and Receiver Square-Wave Output Using ÷ 2 Flip-Flop
Figure 27. Voltage-to-Frequency Converter With Figure 28. Voltage-to-Frequency Converter With
Isolators Isolators
Figure 29. Voltage-to-Frequency Converter With Figure 30. Voltage-to-Frequency Converter With
Isolators Isolators
Copyright © 1999–2015, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Links: LM231 LM331
COMP-OUT
1
COMP-OUT
6
COMP-OUT
1
COMP-OUT
2
IREF
3
FOUT
4
GND
7
VINF
8
VS
5
RC_TIME
1
RC_TIME
2
GND
2
LOAD
1
VINF
2
GND
GND
LM231
,
LM331
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
www.ti.com
10 Power Supply Recommendations
The LMx31 can operate over a wide supply voltage range of 4 V to 40 V. For proper operation, the supply pin
should be bypassing to ground with a low-ESR, 1-µF capacitor. It is acceptable to use X7R capacitors for this.
For systems using higher supply voltages, ensure that the voltage rating for the bypass caps is sufficient.
11 Layout
11.1 Layout Guidelines
Bypass capacitors must be placed as close as possible to the supply pin. As the LM331 is a through-hole device,
it is acceptable to place the bypass capacitor on the bottom layer.
If an input capacitor to ground is used to clean the input signal, the capacitor should be placed close to the
supply pin.
Use of a ground plane is recommended to provide a low-impedance ground across the circuit.
11.2 Layout Example
Figure 31. Layout Example
18 Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated
Product Folder Links: LM231 LM331
LM231
,
LM331
www.ti.com
SNOSBI2C –JUNE 1999–REVISED SEPTEMBER 2015
12 Device and Documentation Support
12.1 Related Links
The table below lists quick access links. Categories include technical documents, support and community
resources, tools and software, and quick access to sample or buy.
Table 1. Related Links
TECHNICAL TOOLS & SUPPORT &
PARTS PRODUCT FOLDER SAMPLE & BUY DOCUMENTS SOFTWARE COMMUNITY
LM231 Click here Click here Click here Click here Click here
LM331 Click here Click here Click here Click here Click here
12.2 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.3 Trademarks
E2E is a trademark of Texas Instruments.
Teflon is a registered trademark of E.
All other trademarks are the property of their respective owners.
12.4 Electrostatic Discharge Caution
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.
12.5 Glossary
SLYZ022 —TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
Copyright © 1999–2015, Texas Instruments Incorporated Submit Documentation Feedback 19
Product Folder Links: LM231 LM331
PACKAGE OPTION ADDENDUM
www.ti.com 11-Jan-2021
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead finish/
Ball material
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LM231AN/NOPB ACTIVE PDIP P 8 40 RoHS & Green Call TI | SN Level-1-NA-UNLIM -25 to 85 LM
231AN
LM231N/NOPB ACTIVE PDIP P 8 40 RoHS & Green Call TI | SN Level-1-NA-UNLIM -25 to 85 LM
231N
LM331AN/NOPB ACTIVE PDIP P 8 40 RoHS & Green Call TI | SN Level-1-NA-UNLIM LM
331AN
LM331N/NOPB ACTIVE PDIP P 8 40 RoHS & Green Call TI | SN Level-1-NA-UNLIM 0 to 70 LM
331N
(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 <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two
lines if the finish value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
PACKAGE OPTION ADDENDUM
www.ti.com 11-Jan-2021
Addendum-Page 2
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable
standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you
permission to use these resources only for development of an application that uses the TI products described in the resource. Other
reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third party
intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims, damages,
costs, losses, and liabilities arising out of your use of these resources.
TI’s products are provided subject to TI’s Terms of Sale (https:www.ti.com/legal/termsofsale.html) or other applicable terms available either
on ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s
applicable warranties or warranty disclaimers for TI products.IMPORTANT NOTICE
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2021, Texas Instruments Incorporated
