ADVFC32SH(RevA) View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADVFC32SH
(Rev.:RevA)

Voltage-to-Frequency and Frequency-to-Voltage Converter

Analog Devices 

ADVFC32

Figure 6. High Noise Immunity Data Link

fiber link, and the optocoupler provides common-mode isolation

up to 3000 V dc.

The data link input voltage is changed in a frequency modulated

signal by the first ADVFC32. A 42.2 kΩ input resistor and a

100 kΩ offset resistor set the scaling so that a 0 V input signal

corresponds to 50 kHz, and a 10 V input results in the maxi-

mum output frequency of 500 kHz. A high frequency opto-

coupler is then used to transmit the signal across any common-

mode voltage potentials to the receiving ADVFC32. The opto-

coupler is not necessary in systems where common-mode noise

is either very small or a constant low level dc voltage. In systems

where common-mode voltage may present a problem, the con-

nection between the two locations should be through the opto-

coupler; no power or ground connections need to be made.

The output of the optocoupler drives an ADVFC32 hooked up

in the F/V configuration. Since the reconstructed signal at Pin

10 has a considerable amount of carrier feedthrough, it is desir-

able to filter out any frequencies in the carrier range of 50 kHz

to 500 kHz. The frequency response of the F/V converter is only

3 kHz due to the pole made by the integrator, so a second 3 kHz

filter will not significantly limit the bandwidth. With the simple

one pole filter shown in Figure 6, the input to output 3 dB point

is approximately 2 kHz, and the output noise is less than

15 mV. If a lower output impedance drive is needed, a two pole

active filter is recommended as an output stage.

Although the F/V conversion technique used in this circuit is

quite simple, it is also very limited in terms of its frequency re-

sponse and output ripple. The frequency response is limited by

the integrator time constant and while it is possible to decrease

that time constant, either signal range or output ripple must be

sacrificed. The performance of the circuit of Figure 6 is shown

in the photograph below. The top trace is the input signal, the

middle trace is the frequency-modulated signal at the

optocoupler’s output, and the bottom trace is the recovered

signal at the output of the F/V converter.

14-Pin Plastic DIP Package

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

TO-100 Package

–6–

REV. A

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