Product Folder Sample & Buy Support & Community Tools & Software Technical Documents 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 are ideally suited for use in simple low-cost circuits for analog-to-digital conversion, precision frequencyto-voltage conversion, long-term integration, linear frequency modulation or demodulation, and many other functions. The output when used as a voltageto-frequency converter is a pulse train at a frequency precisely proportional to the applied input voltage. Thus, it provides all the inherent advantages of the voltage-to-frequency conversion techniques, and is easy to apply in all standard voltage-to-frequency converter applications. 1 • • • • • • • • Ensured Linearity 0.01% Maximum Improved Performance in Existing Voltage-toFrequency Conversion Applications Split or Single-Supply Operation Operates on Single 5-V Supply Pulse Output Compatible With All Logic Forms Excellent Temperature Stability: ±50 ppm/°C Maximum Low Power Consumption: 15 mW Typical at 5 V Wide Dynamic Range, 100 dB Minimum at 10-kHz Full Scale Frequency Wide Range of Full Scale Frequency: 1 Hz to 100 kHz Low-Cost 2 Applications • • • • Device Information(1) PART NUMBER LM231 LM331 PACKAGE PDIP (8) BODY SIZE (NOM) 9.81 mm × 6.35 mm (1) For all available packages, see the orderable addendum at 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 1 2 3 4 5 6 7 8 Features .................................................................. Applications ........................................................... Description ............................................................. Revision History..................................................... Description continued ........................................... Pin Configuration and Functions ......................... Specifications......................................................... 1 1 1 2 3 4 4 7.1 7.2 7.3 7.4 7.5 7.6 7.7 4 4 5 5 5 6 7 Absolute Maximum Ratings ...................................... ESD Ratings.............................................................. Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Dissipation Ratings ................................................... Typical Characteristics .............................................. Detailed Description .............................................. 9 8.1 Overview ................................................................... 9 8.2 Functional Block Diagram ......................................... 9 8.3 Feature Description................................................. 10 8.4 Device Functional Modes........................................ 10 9 Application and Implementation ........................ 11 9.1 Application Information............................................ 11 9.2 Typical Applications ................................................ 12 9.3 System Examples .................................................. 15 10 Power Supply Recommendations ..................... 18 11 Layout................................................................... 18 11.1 Layout Guidelines ................................................. 18 11.2 Layout Example .................................................... 18 12 Device and Documentation Support ................. 19 12.1 12.2 12.3 12.4 12.5 Related Links ........................................................ Community Resources.......................................... Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 19 19 19 19 19 13 Mechanical, Packaging, and Orderable Information ........................................................... 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 • 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 • 2 Page Page Changed layout of National Data Sheet to TI format ............................................................................................................. 1 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 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. Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated Product Folder Links: LM231 LM331 3 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 NAME NO. IOUT 1 IREF FOUT I/O DESCRIPTION O Current Output 2 I Reference Current 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 40 V +VS V 260 °C Supply Voltage, VS Output Short Circuit to Ground Continuous Output Short Circuit to VCC Continuous −0.2 Input Voltage Lead Temperature (Soldering, 10 sec.) (1) (2) (3) PDIP 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. All voltages are measured with respect to GND = 0 V, unless otherwise noted. If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications. 7.2 ESD Ratings V(ESD) (1) (2) 4 Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) (2) VALUE UNIT ±500 V JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. Human body model, 100 pF discharged through a 1.5-kΩ resistor. 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 7.3 Recommended Operating Conditions Operating Ambient Temperature MIN MAX LM231, LM231A −25 85 °C LM331, LM331A 0 70 °C 4 40 V Supply Voltage, VS (1) (1) UNIT 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 (1) Junction-to-ambient thermal resistance 100 °C/W 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 VFC Non-Linearity TEST CONDITIONS MIN TYP MAX UNIT 4.5 V ≤ VS ≤ 20 V ±0.003 ±0.01 % FullScale TMIN ≤ TA ≤ TMAX ±0.006 ±0.02 % FullScale VS = 15 V, f = 10 Hz to 11 kHz ±0.024 ±0.14 %FullScale 0.95 1 1.05 kHz/V 0.9 1 1.1 kHz/V TMIN ≤ TA ≤ TMAX 4.5 V ≤ VS ≤ 20 V ±30 ±150 ppm/°C ±20 ±50 ppm/°C 4.5 V ≤ VS ≤ 10 V 0.01 0.1 %/V 10 V ≤ VS ≤ 40 V 0.006 0.06 %/V (1) VFC Non-Linearity in Circuit of Figure 14 Conversion Accuracy Scale Factor (Gain) Temperature Stability of Gain LM231, LM231A VIN = −10 V, RS = 14 kΩ LM331, LM331A LMx31 LMx31A Change of Gain with VS Rated Full-Scale Frequency VIN = −10 V Gain Stability vs. Time (1000 Hours) TMIN ≤ TA ≤ TMAX Over Range (Beyond Full-Scale) Frequency VIN = −11 V 10.0 kHz % FullScale ±0.02 10% INPUT COMPARATOR Offset Voltage LM231/LM331 TMIN ≤ TA ≤ TMAX LM231A/LM331A TMIN ≤ TA ≤ TMAX Bias Current Offset Current Common-Mode Range TMIN ≤ TA ≤ TMAX ±3 ±10 mV ±4 ±14 mV ±3 ±10 mV −80 −300 nA ±8 ±100 nA VCC − 2 V −0.2 TIMER Timer Threshold Voltage, Pin 5 Input Bias Current, Pin 5 0.667 × VS 0.7 × VS 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 0.22 0.5 V VSAT PIN 5 (Reset) (1) 0.63 × VS VS = 15 V I = 5 mA 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. Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated Product Folder Links: LM231 LM331 5 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 126 135 144 μA 116 136 156 μA 0.2 1 μA 0.02 10 nA 2 50 nA CURRENT SOURCE (PIN 1) LM231, LM231A Output Current 0V ≤ VPIN 1 ≤ 10 V Change with Voltage Current Source OFF Leakage RS = 14 kΩ, VPIN 1 = 0 LM331, LM331A LM231, LM231A, LM331, LM331A All Devices TA = TMAX Operating Range of Current (Typical) μA (10 to 500) REFERENCE VOLTAGE (PIN 2) LM231, LM231A 1.76 1.89 2.02 LM331, LM331A 1.7 1.89 2.08 Stability vs. Temperature ±60 Stability vs. Time, 1000 Hours VDC VDC ppm/°C ±0.1% LOGIC OUTPUT (PIN 3) I = 5 mA VSAT 0.15 0.5 V 0.1 0.4 V ±0.05 1 μA 2 3 4 mA VS = 40 V 2.5 4 6 mA VS = 5 V 1.5 3 6 mA 2 4 8 mA I = 3.2 mA (2 TTL Loads), TMIN ≤ TA ≤ TMAX OFF Leakage SUPPLY CURRENT LM231, LM231A LM331, LM331A VS = 5 V VS = 40 V 7.6 Dissipation Ratings Package Dissipation at 25°C (1) (1) 6 VALUE UNIT 1.25 W 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. 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 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 16) Figure 2. Non-Linearity Error Figure 3. Non-Linearity Error vs. Power Supply Voltage Figure 4. Frequency vs. Temperature Figure 5. VREF vs. Temperature Figure 6. Output Frequency vs. VSUPPLY Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated Product Folder Links: LM231 LM331 7 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.) 8 Figure 7. 100 kHz Non-Linearity Error (Figure 17) Figure 8. Non-Linearity Error (Figure 14) Figure 9. Input Current (Pins 6,7) vs. Temperature Figure 10. Power Drain vs. VSUPPLY Figure 11. Output Saturation Voltage vs. IOUT (Pin 3) Figure 12. Non-Linearity Error, Precision F-to-V Converter (Figure 19) 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 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 VS range 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/RS to 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 RtCt network. 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 ⅔ VCC, 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 Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated Product Folder Links: LM231 LM331 9 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 ⅔ VCC, 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 Vx up 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 CL will be gradually discharged by RL until Vx falls to the level of V1. Then the comparator will trigger the timer and start another cycle. The current flowing into CL is exactly IAVE = i × (1.1×RtCt) × f, and the current flowing out of CL is 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-tofrequency (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 Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated Product Folder Links: LM231 LM331 11 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 kΩ to 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 RS at pin 2 is made up of a 12-kΩ fixed 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, RL and 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-Ω resistor 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 Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated Product Folder Links: LM231 LM331 13 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 kΩ or 10 kΩ for VS = 8 V to 22 V, but must be 10 kΩ for 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 kΩ and 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 kΩ or 10 kΩ for VS=8V to 22V, but must be 10 kΩ for 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 Converter Figure 18. Simple Frequency-to-Voltage Converter Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated Product Folder Links: LM231 LM331 15 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 Converter, Figure 20. Light Intensity to Frequency Converter Figure 21. Temperature to Frequency Converter Figure 22. Long-Term Digital Integrator Using VFC Figure 23. Basic Analog-to-Digital Converter Using Voltage-to-Frequency Converter Figure 24. Analog-to-Digital Converter With Microprocessor 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 With 2-Wire Transmitter and Receiver Figure 26. Voltage-to-Frequency Converter With Square-Wave Output Using ÷ 2 Flip-Flop Figure 27. Voltage-to-Frequency Converter With Isolators Figure 28. Voltage-to-Frequency Converter With Isolators Figure 29. Voltage-to-Frequency Converter With Isolators Figure 30. Voltage-to-Frequency Converter With Isolators Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated Product Folder Links: LM231 LM331 17 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. GND 11.2 Layout Example 2 GND 1 COMP-OUT 8 VS C O M P- O U 2 IREF T 7 VINF 3 FOUT 6 COMP-OUT 4 GND 5 RC_TIME 1 VINF 1 COMP-OUT 2 LOAD 1 RC_TIME 2 GND 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 PARTS PRODUCT FOLDER SAMPLE & BUY TECHNICAL DOCUMENTS TOOLS & SOFTWARE SUPPORT & 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. Submit Documentation Feedback Copyright © 1999–2015, Texas Instruments Incorporated Product Folder Links: LM231 LM331 19 PACKAGE OPTION ADDENDUM www.ti.com 8-Aug-2015 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (°C) Device Marking (4/5) LM231AN/NOPB ACTIVE PDIP P 8 40 Green (RoHS & no Sb/Br) CU SN Level-1-NA-UNLIM -25 to 85 LM 231AN LM231N/NOPB ACTIVE PDIP P 8 40 Green (RoHS & no Sb/Br) CU SN Level-1-NA-UNLIM -25 to 85 LM 231N LM331AN/NOPB ACTIVE PDIP P 8 40 Green (RoHS & no Sb/Br) CU SN Level-1-NA-UNLIM LM331N/NOPB ACTIVE PDIP P 8 40 Green (RoHS & no Sb/Br) CU SN Level-1-NA-UNLIM 0 to 70 LM 331N RC4151NB OBSOLETE PDIP P 8 TBD Call TI Call TI 0 to 70 LM 331N RV4151NB OBSOLETE PDIP P 8 TBD Call TI Call TI -25 to 85 LM 231N LM 331AN (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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (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. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 8-Aug-2015 (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish 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. 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