LM331N

LM231A/231/331A/331 LM231A/LM231/LM331A/LM331 Precision Voltage-to-Frequency Converters FEATURES DESCRIPTION • • The LM231/LM331 family of voltage-to-frequency converters are ideally suited for use in simple lowcost circuits for analog-to-digital conversion, precision frequency-to-voltage conversion, long-term integration, linear frequency modulation or demodulation, and many other functions. The output when used as a voltage-to-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. Further, the LM231A/LM331A attain a new high level of accuracy versus temperature which could only be attained with expensive voltage-to-frequency modules. Additionally the LM231/331 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 voltageto-frequency converter can be easily channeled through a simple photo isolator to provide isolation against high common mode levels. 1 23 • • • • • • • • Ensured Linearity 0.01% max Improved Performance in Existing Voltage-toFrequency Conversion Applications Split or Single Supply Operation Operates on Single 5V Supply Pulse Output Compatible with All Logic Forms Excellent Temperature Stability: ±50 ppm/°C max Low Power Consumption: 15 mW Typical at 5V Wide Dynamic Range, 100 dB min at 10 kHz Full Scale Frequency Wide Range of Full Scale Frequency: 1 Hz to 100 kHz Low Cost The LM231/LM331 utilize a new temperaturecompensated band-gap reference circuit, to provide excellent accuracy over the full operating temperature range, at power supplies as low as 4.0V. 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 40V, yet is short-circuit-proof against VCC. CONNECTION DIAGRAM Figure 1. Plastic Dual-In-Line Package (PDIP) See Package Number P (R-PDIP-T8) http://www.hgsemi.com.cn 1 2017 MAR LM231A/231/331A/331 Absolute Maximum Ratings (1) (2) (3) Supply Voltage, VS 40V Output Short Circuit to Ground Continuous Output Short Circuit to VCC Continuous −0.2V to +VS Input Voltage Package Dissipation at 25°C 1.25W (4) Lead Temperature (Soldering, 10 sec.) PDIP 260°C ESD Susceptibility (1) (2) (3) (4) (5) (5) 500V Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating the device beyond its specified operating conditions. All voltages are measured with respect to GND = 0V, unless otherwise noted. If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications. 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. Human body model, 100 pF discharged through a 1.5 kΩ resistor. Operating Ratings (1) Operating Ambient Temperature LM231, LM231A −25°C to +85°C LM331, LM331A 0°C to +70°C Supply Voltage, VS +4V to +40V (1) All voltages are measured with respect to GND = 0V, unless otherwise noted. Package Thermal Resistance Package θJ-A 8-Lead PDIP 100°C/W Electrical Characteristics All specifications apply in the circuit of Figure 16, with 4.0V ≤ VS ≤ 40V, TA=25°C, unless otherwise specified. Parameter VFC Non-Linearity (1) VFC Non-Linearity in Circuit of Figure 15 Typ Max Units 4.5V ≤ VS ≤ 20V Conditions Min ±0.003 ±0.01 % Full- Scale TMIN ≤ TA ≤ TMAX ±0.006 ±0.02 % Full- Scale VS = 15V, f = 10 Hz to 11 kHz ±0.024 ±0.14 %Full- Scale 0.95 1.00 1.05 kHz/V 0.90 1.00 1.10 kHz/V TMIN ≤ TA ≤ TMAX, 4.5V ≤ VS ≤ 20V ±30 ±150 ppm/°C ±20 ±50 ppm/°C 4.5V ≤ VS ≤ 10V 0.01 0.1 %/V 10V ≤ VS ≤ 40V 0.006 0.06 %/V Conversion Accuracy Scale Factor (Gain) LM231, LM231A VIN = −10V, RS = 14 kΩ LM331, LM331A Temperature Stability of Gain LM231/LM331 LM231A/LM331A Change of Gain with VS Rated Full-Scale Frequency VIN = −10V Gain Stability vs. Time (1000 Hours) TMIN ≤ TA ≤ TMAX (1) 10.0 kHz ±0.02 % Full- Scale Nonlinearity 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. http://www.hgsemi.com.cn 2 2017 MAR LM231A/231/331A/331 Electrical Characteristics (continued) All specifications apply in the circuit of Figure 16, with 4.0V ≤ VS ≤ 40V, TA=25°C, unless otherwise specified. Parameter Over Range (Beyond Full-Scale) Frequency Conditions VIN = −11V Min Typ Max 10 Units % INPUT COMPARATOR Offset Voltage ±3 ±10 mV LM231/LM331 TMIN ≤ TA ≤ TMAX ±4 ±14 mV LM231A/LM331A TMIN ≤ TA ≤ TMAX ±3 ±10 mV −80 −300 nA ±8 ±100 nA VCC−2. 0 V 0.70 × VS Bias Current Offset Current Common-Mode Range TMIN ≤ TA ≤ TMAX −0.2 TIMER Timer Threshold Voltage, Pin 5 Input Bias Current, Pin 5 0.63 0.667 VS = 15V All Devices 0V ≤ VPIN 5 ≤ 9.9V ±10 ±100 nA LM231/LM331 VPIN 5 = 10V 200 1000 nA LM231A/LM331A VPIN 5 = 10V 200 500 nA I = 5 mA 0.22 0.5 V 126 135 144 μA 116 136 156 μA 0.2 1.0 μA 0.02 10.0 nA 2.0 50.0 VSAT PIN 5 (Reset) CURRENT SOURCE (Pin 1) Output Current LM231, LM231A RS = 14 kΩ, VPIN 1 = 0 LM331, LM331A Change with Voltage 0V ≤ VPIN 1 ≤ 10V Current Source OFF Leakage LM231, LM231A, LM331, LM331A All Devices TA = TMAX Operating Range of Current (Typical) nA μA (10 to 500) REFERENCE VOLTAGE (Pin 2) LM231, LM231A 1.76 1.89 2.02 VDC LM331, LM331A 1.70 1.89 2.08 VDC Stability vs. Temperature ±60 ppm/°C Stability vs. Time, 1000 Hours ±0.1 % LOGIC OUTPUT (Pin 3) VSAT I = 5 mA 0.15 0.50 V I = 3.2 mA (2 TTL Loads), TMIN ≤ TA ≤ TMAX 0.10 0.40 V ±0.05 1.0 μA OFF Leakage SUPPLY CURRENT LM231, LM231A LM331, LM331A http://www.hgsemi.com.cn VS = 5V 2.0 3.0 4.0 mA VS = 40V 2.5 4.0 6.0 mA VS = 5V 1.5 3.0 6.0 mA VS = 40V 2.0 4.0 8.0 mA 3 2017 MAR LM231A/231/331A/331 FUNCTIONAL BLOCK DIAGRAM Pin numbers apply to 8-pin packages only. http://www.hgsemi.com.cn 4 2017 MAR LM231A/231/331A/331 TYPICAL PERFORMANCE CHARACTERISTICS (All electrical characteristics apply for the circuit of Figure 16, unless otherwise noted.) Nonlinearity Error as Precision V-to-F Converter (Figure 16) Nonlinearity Error Figure 2. Figure 3. Nonlinearity Error vs. Power Supply Voltage Frequency vs. Temperature Figure 4. Figure 5. VREF vs. Temperature Output Frequency vs. VSUPPLY Figure 6. Figure 7. http://www.hgsemi.com.cn 5 2017 MAR LM231A/231/331A/331 TYPICAL PERFORMANCE CHARACTERISTICS (continued) (All electrical characteristics apply for the circuit of Figure 16, unless otherwise noted.) 100 kHz Nonlinearity Error (Figure 17) Nonlinearity Error (Figure 15) Figure 8. Figure 9. Input Current (Pins 6,7) vs. Temperature Power Drain vs. VSUPPLY Figure 10. Figure 11. Output Saturation Voltage vs. IOUT (Pin 3) Nonlinearity Error, Precision F-to-V Converter (Figure 19) Figure 12. Figure 13. http://www.hgsemi.com.cn 6 2017 MAR LM231A/231/331A/331 APPLICATIONS INFORMATION PRINCIPLES OF OPERATION The LM231/331 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 LM231/331 is shown in Figure 14 and consists of a switched current source, input comparator, and 1-shot timer. Figure 14. Simplified Block Diagram of Stand-Alone Voltage-to-Frequency Converter and External Components 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 14, which consists of the simplified block diagram of the LM231/331 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. Detail of Operation, Functional Block Diagram The block diagram (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 3.9V to 40V. 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 1.9V, and causes a current i=1.90V/RS to flow. For Rs=14k, 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 RS flip-flop. The timing function consists of an RS 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 RS 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 RS flip-flop to reset. The reset transistor is then turned ON and the current switch is turned OFF. http://www.hgsemi.com.cn 7 2017 MAR LM231A/231/331A/331 However, if the input comparator still detects pin 7 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. The output driver transistor acts to saturate pin 3 with an ON resistance of about 50Ω. In case of over voltage, the output current is actively limited to less than 50 mA. 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 care must be taken to ensure that current is not taken from it which could reduce the accuracy of the converter. Basic Voltage-to-Frequency Converter (Figure 15) The simple stand-alone V-to-F converter shown in Figure 15 includes all the basic circuitry of Figure 14 plus a few components for improved performance. A resistor, RIN=100 kΩ ±10%, has been added in the path to pin 7, so that the bias current at pin 7 (−80 nA typical) will cancel the effect of the bias current at pin 6 and help provide minimum frequency offset. 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 LM231/331, and the tolerance of Rt, RL and Ct. 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. A capacitor CIN is added from pin 7 to ground to act as a filter for VIN. 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. A 47Ω resistor, in series with the 1 μF CL, provides hysteresis, which helps the input comparator provide the excellent linearity. *Use stable components with low temperature coefficients. See APPLICATIONS INFORMATION. **0.1μF or 1μF, See PRINCIPLES OF OPERATION. Figure 15. Simple Stand-Alone V-to-F Converter with ±0.03% Typical Linearity (f = 10 Hz to 11 kHz) http://www.hgsemi.com.cn 8 2017 MAR LM231A/231/331A/331 Details of Operation: Precision V-To-F Converter (Figure 16) 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 LM231/331, the timing cycle is initiated. The average current fed into the op-amp's summing point (pin 2) is i × (1.1 RtCt) × f which is perfectly balanced with −VIN/RIN. In this circuit, the voltage offset of the LM231/331 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 2 output pulses' spacing 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. See APPLICATIONS INFORMATION. **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 type LF411A Figure 16. Standard Test Circuit and Applications Circuit, Precision Voltage-to-Frequency Converter DETAILS OF OPERATION: F-to-V CONVERTERS (Figure 18 and Figure 19) 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. http://www.hgsemi.com.cn 9 2017 MAR LM231A/231/331A/331 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. *Use stable components with low temperature coefficients. See APPLICATIONS INFORMATION. **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, 100 kHz Full-Scale, ±0.03% Non-Linearity *Use stable components with low temperature coefficients. Figure 18. Simple Frequency-to-Voltage Converter, 10 kHz Full-Scale, ±0.06% Non-Linearity http://www.hgsemi.com.cn 10 2017 MAR LM231A/231/331A/331 *Use stable components with low temperature coefficients. Figure 19. Precision Frequency-to-Voltage Converter, 10 kHz Full-Scale with 2-Pole Filter, ±0.01% Non-Linearity Maximum *L14F-1, L14G-1 or L14H-1, photo transistor (General Electric Co.) or similar Figure 20. Light Intensity to Frequency Converter Figure 21. Temperature to Frequency Converter http://www.hgsemi.com.cn 11 2017 MAR LM231A/231/331A/331 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 Figure 25. Remote Voltage-to-Frequency Converter with 2-Wire Transmitter and Receiver http://www.hgsemi.com.cn 12 2017 MAR LM231A/231/331A/331 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 http://www.hgsemi.com.cn 13 2017 MAR LM231A/231/331A/331 Figure 29. Voltage-to-Frequency Converter with Isolators Figure 30. Voltage-to-Frequency Converter with Isolators http://www.hgsemi.com.cn 14 2017 MAR LM231A/231/331A/331 Schematic Diagram http://www.hgsemi.com.cn 15 2017 MAR