DETAILS OF OPERATION, FREQUENCY-TO-

VOLTAGE CONVERTERS (

Figure 6 and Figure 7)

In these applications, a pulse input at f

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

I

In the simple circuit of

Figure 6, this current is filtered in the

network R

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 6.

However, for input frequencies below 200 Hz, this circuit will

have worse ripple than

Figure 6. 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.

DS005680-6

See Typical Applications section.

FIGURE 5. Precision Voltage-to-Frequency Converter,

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