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a FEATURES Low Cost Single or Dual Supply, 5 V to 36 V, ؎5 V to ؎18 V Full-Scale Frequency Up to 500 kHz Minimum Number of External Components Needed Versatile Input Amplifier Positive or Negative Voltage Modes Negative Current Mode High Input Impedance, Low Drift Low Power: 2.0 mA Quiescent Current Low Offset: 1 mV

Low Cost Monolithic Voltage-to-Frequency Converter AD654 FUNCTIONAL BLOCK DIAGRAM



The AD654 is a monolithic V/F converter consisting of an input amplifier, a precision oscillator system, and a high current output stage. A single RC network is all that is required to set up any full scale (FS) frequency up to 500 kHz and any FS input voltage up to ± 30 V. Linearity error is only 0.03% for a 250 kHz FS, and operation is guaranteed over an 80 dB dynamic range. The overall temperature coefficient (excluding the effects of external components) is typically ± 50 ppm/°C. The AD654 operates from a single supply of 5 V to 36 V and consumes only 2.0 mA quiescent current.

1. Packaged in both an 8-pin mini-DIP and an 8-pin SOIC package, the AD654 is a complete V/F converter requiring only an RC timing network to set the desired full-scale frequency and a selectable pullup resistor for the open-collector output stage. Any full scale input voltage range from 100 mV to 10 volts (or greater, depending on +VS) can be accommodated by proper selection of the timing resistor. The fullscale frequency is then set by the timing capacitor from the simple relationship, f = V/10 RC.

The low drift (4 µV/°C typ) input amplifier allows operation directly from small signals such as thermocouples or strain gauges while offering a high (250 MΩ) input resistance. Unlike most V/F converters, the AD654 provides a square-wave output, and can drive up to 12 TTL loads, optocouplers, long cables, or similar loads.

2. A minimum number of low cost external components are necessary. A single RC network is all that is required to set up any full scale frequency up to 500 kHz and any full-scale input voltage up to ± 30 V. 3. Plastic packaging allows low cost implementation of the standard VFC applications: A/D conversion, isolated signal transmission, F/V conversion, phase-locked loops, and tuning switched-capacitor filters. 4. Power supply requirements are minimal; only 2.0 mA of quiescent current is drawn from the single positive supply from 4.5 volts to 36 volts. In this mode, positive inputs can vary from 0 volts (ground) to (+VS –4) volts. Negative inputs can easily be connected for below ground operation. 5. The versatile open-collector output stage can sink more than 10 mA with a saturation voltage less than 0.4 volts. The Logic Common terminal can be connected to any level between ground (or –VS) and 4 volts below +VS. This allows easy direct interface to any logic family with either positive or negative logic levels.

REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703

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