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LM231A/LM231/LM331A/LM331 Precision Voltage-to-Frequency Converters

June 1999

LM231A/LM231/LM331A/LM331 Precision Voltage-to-Frequency Converters
General Description
The LM231/LM331 family of voltage-to-frequency converters are ideally suited for use in simple low-cost circuits for analog-to-digital conversion, precision frequency-to-voltage conversion, long-term integration, linearfrequency 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, theLM231A/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 voltage-to-frequencyconverter can be easily channeled through a simple photoisolator to provide isolation against high common mode levels. The LM231/LM331 utilize a new temperature-compensated band-gap reference circuit, to provide excellent accuracy over the full operating temperature range, at power supplies as low as 4.0V. The precision timer circuit has low bias currents without degrading the quick response necessaryfor 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.

n Guaranteed linearity 0.01% max n Improved performance in existing voltage-to-frequency conversion applications n Split or single supply operation n Operates on single 5V supply n Pulse output compatible with alllogic forms n Excellent temperature stability, ± 50 ppm/˚C max n Low power dissipation, 15 mW typical at 5V n Wide dynamic range, 100 dB min at 10 kHz full scale frequency n Wide range of full scale frequency, 1 Hz to 100 kHz n Low cost

Typical Applications


*Use stable components with low temperature coefficients. See Typical Applications section. **0.1µF or 1µF, See “Principlesof Operation.”

FIGURE 1. Simple Stand-Alone Voltage-to-Frequency Converter with ± 0.03% Typical Linearity (f = 10 Hz to 11 kHz)

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© 1999 National Semiconductor Corporation


Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor SalesOffice/ Distributors for availability and specifications. Supply Voltage Output Short Circuit to Ground Output Short Circuit to VCC Input Voltage Operating Ambient Temperature Range Power Dissipation (PD at 25˚C) and Thermal Resistance (θjA) (N Package) PD θjA Lead Temperature (Soldering, 10 sec.) Dual-In-Line Package (Plastic) ESD Susceptibility (Note 4) N Package LM231A/LM231 40V ContinuousContinuous −0.2V to +VS TMIN TMAX −25˚C to +85˚C LM331A/LM331 40V Continuous Continuous −0.2V to +VS TMIN TMAX 0˚C to +70˚C

1.25W 100˚C/W 260˚C 500V

1.25W 100˚C/W 260˚C 500V

Electrical Characteristics
TA = 25˚C unless otherwise specified (Note 2) Parameter VFC Non-Linearity (Note 3) Conditions 4.5V ≤ VS ≤ 20V TMIN ≤ TA ≤ TMAX VFC Non-Linearity In Circuit of Figure 1 Conversion Accuracy ScaleFactor (Gain) LM231, LM231A LM331, LM331A Temperature Stability of Gain LM231/LM331 LM231A/LM331A Change of Gain with VS Rated Full-Scale Frequency Gain Stability vs Time (1000 Hrs) Overrange (Beyond Full-Scale) Frequency INPUT COMPARATOR Offset Voltage LM231/LM331 LM231A/LM331A Bias Current Offset Current Common-Mode Range TIMER Timer Threshold Voltage, Pin 5 Input Bias Current, Pin 5 All Devices...
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