LM331N datasheet(8/16 Pages) NSC

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Typical Applications (Continued)

DETAILS OF OPERATION FREQUENCY-TO-

VOLTAGE CONVERTERS

(FIGURES 5 AND 6 )

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 e i c (11 RtCt) c f

In the simple circuit of

FIGURE 5 this current is filtered in

the network RL e 100 kX and 1 mF The ripple will be less

than 10 mV peak but the response will be slow with a

01 second time constant and settling of 07 second to

01% 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 5

However for input frequencies below 200 Hz this circuit will

have worse ripple than

Figure 5 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

TLH5680 – 6

Use stable components with low temperature coefficients

See Typical Applications section

This resistor can be 5 kX or 10 kX for VSe8V to 22V

but must be 10 kX for VSe45V to 8V

Use low offset voltage and low offset current op amps for A1

recommended types LF411A or LF356

FIGURE 4 Precision Voltage-to-Frequency Converter

100 kHz Full-Scale g003% Non-Linearity

TLH5680 – 7

VOUT e fIN c 209V c

(RtCt)

Use stable components with low temperature coefficients

FIGURE 5 Simple Frequency-to-Voltage Converter

10 kHz Full-Scale g006% Non-Linearity

VOUT ebfIN c 209V c

(RtCt)

TLH5680 – 8

SELECT Rx e

(VS b 2V)

02 mA

Use stable components with low temperature coefficients

FIGURE 6 Precision Frequency-to-Voltage Converter

10 kHz Full-Scale with 2-Pole Filter g001%

Non-Linearity Maximum

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