LM231, LM331

SNOSBI2B – JUNE 1999 – REVISED MARCH 2013

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However, if the input comparator still detects pin 7 higher than pin 6 when pin 5 crosses

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 50

Ω. In case of over voltage,

the output current is actively limited to less than 50 mA.

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.

typical) will cancel the effect of the bias current at pin 6 and help provide minimum frequency offset.

rheostat. The function of this adjustment is to trim out the gain tolerance of the LM231/331, and the tolerance of

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.

adequate in most cases; however, in cases where better filtering is required, a 1

μF capacitor can be used.

A 47

excellent linearity.

*Use stable components with low temperature coefficients. See APPLICATIONS INFORMATION.

**0.1

μF 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)

8

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