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Low Cost Monolithic Voltage-to-Frequency Converter

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Brands: Analog Devices, Inc

Mfr.Part #: AD654

Datasheet: AD654 Datasheet (PDF)

Package/Case: SOP-8

Product Type: Power Supplies

RoHS Status:

Stock Condition: 3245 pcs, New Original

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AD654 General Description

AD654 V/F converter is a versatile integrated circuit that offers precise voltage-to-frequency conversion with excellent linearity, wide operating voltage and frequency ranges, and low power consumption. It is suitable for applications involving signal conditioning, frequency modulation, and more. Additionally, its ability to generate a square-wave output and drive multiple loads enhances its versatility in various electronic systems.

The AD654 is an integrated circuit that serves as a V/F converter. It consists of an input amplifier, a precision oscillator system, and a high-current output stage.

A single resistor-capacitor (RC) network can be used to set the full-scale (FS) output frequency, with a maximum frequency of 500 kHz.

The AD654 can accommodate input voltages in the range of ±30 V. This wide input voltage range makes it suitable for various applications.

The linearity error is exceptionally low, typically only 0.03% for a 250 kHz full-scale frequency.

It offers reliable operation over an 80 dB dynamic range, making it suitable for applications with varying input signal levels.

The overall temperature coefficient (excluding external components) is typically ±50 ppm/°C. This indicates good stability over temperature variations.

The AD654 operates from a single supply voltage ranging from 5 V to 36 V.

It consumes only 2.0 mA of quiescent current, which is beneficial for low-power or battery-powered applications.

The input amplifier exhibits low drift, with a typical drift rate of 4 µV/°C. This makes it suitable for amplifying small signals, such as those from thermocouples or strain gauges.

Unlike many V/F converters, the AD654 provides a square-wave output signal.

It can drive up to 12 TTL (Transistor-Transistor Logic) loads, optocouplers, long cables, or similar loads, indicating its ability to handle various output requirements.

AD654 Spice Model


2D Model and Dimensions

Product Highlights

Package Options: The AD654 is available in both an 8-lead mini-DIP package and an 8-lead SOIC (Small Outline Integrated Circuit) package, offering flexibility for different mounting and application requirements.

Simple Configuration: The AD654 serves as a complete voltage-to-frequency converter and requires only a few external components. An RC timing network is used to set the desired full-scale frequency, and a selectable pull-up resistor is used for the open-collector output stage.

Wide Input Voltage Range: The IC can accommodate a wide range of full-scale input voltages, from as low as 100 mV to 10 volts or greater (depending on the positive supply voltage, +VS). Proper selection of the timing resistor allows for this flexibility, and the full-scale frequency is determined by the timing capacitor using the equation f = V / (10 * RC).

Low Component Count: Only a single RC network is required to configure the full-scale frequency up to 500 kHz and full-scale input voltage up to ±30 V, reducing the number of external components needed in a circuit.

Versatile Plastic Packaging: The use of plastic packaging makes the AD654 cost-effective and suitable for various voltage-to-frequency converter (VFC) applications, including A/D conversion, isolated signal transmission, frequency-to-voltage conversion, phase-locked loops (PLLs), and switched-capacitor filter tuning.

Minimal Power Requirements: The AD654 has low power requirements, drawing only 2.0 mA of quiescent current from a single positive supply voltage ranging from 4.5 volts to 36 volts. It accommodates positive inputs ranging from 0 volts to (+VS - 4) volts and allows for easy connection of negative inputs for below-ground operation.

Open-Collector Output Stage: The open-collector output stage is versatile and capable of sinking more than 10 mA of current with a saturation voltage of less than 0.4 volts. The Logic Common terminal can be adjusted to any level between ground (or -VS) and 4 volts below +VS, facilitating direct interface with various logic families, whether they use positive or negative logic levels.

Pinout Configuration


Pin Number Pin Name Description
1 Fout Square Wave Output
2 Logic Common Connects to Supply Ground
3 RT Adjust Output Frequency
4 +Vin Voltage Input
5 -VS -Vcc of Dual Polarity Supply
6 CT Averaging Capacitor
7 CT Averaging Capacitor
8 +VS Connects to Supply Vcc


Low Cost: The AD654 is designed to be cost-effective, making it suitable for a wide range of applications.

Single or Dual Supply: It can operate from a single supply voltage ranging from 5 V to 36 V. This flexibility allows it to work with various power sources.

Wide Full-Scale Frequency Range: The AD654 can generate frequencies with a full-scale (FS) range of up to 500 kHz, providing versatility in signal generation.

Minimal External Components: It requires a minimum number of external components for operation, simplifying circuit design.

Versatile Input Amplifier: The integrated input amplifier is versatile and can be used in both positive and negative voltage modes. It offers high input impedance and low drift.

Negative Current Mode: The IC can operate in a negative current mode, expanding its usability in different configurations.

Low Power Consumption: The quiescent current is low, at 2.0 mA, which is advantageous for battery-powered or energy-efficient applications.

Low Offset Voltage: The offset voltage is minimal, typically only 1 mV, ensuring accurate signal processing.

Maximum Supply Voltage: The IC can handle a maximum supply voltage of 36V.

Input Voltage Range: It can accept input voltages as low as -300 mV to the supply voltage, providing flexibility in input signal levels.

Maximum Output Current: The AD654 can source or sink a maximum output current of 50 mA.

Storage Temperature Range: It is rated to operate within a wide temperature range, from -65°C to +150°C, making it suitable for various environmental conditions.

Full-Scale Calibration Error: The calibration error is specified to be within the range of -10% to +10%, indicating its ability to maintain accuracy in signal conversion.

Absolute Maximum Rating


Parameter Absolute Maximum Rating
Total Supply Voltage (+VS)
+36 V
Total Supply Voltage (-VS) -36 V
Maximum Input Voltage -300 mV to +VS
Maximum Output Current
Instantaneous: 50 mA
Sustained: 25 mA
Logic Common Voltage -500 mV to (+VS - 4)
Storage Temperature Range -65°C to +150°C

Functional block diagram


Two-Wire Temperature-to-Frequency Converter: The AD654 can be used in temperature measurement systems to convert temperature sensor outputs (e.g., thermistors or RTDs) into a frequency signal, allowing for easy transmission of temperature data over a two-wire interface.

Optoisolator Interface for High-Voltage (HV) Systems: In high-voltage systems or applications where electrical isolation is required, the AD654 can interface with optoisolators to safely transmit and receive signals while maintaining isolation between different voltage domains.

AD654 With Stand-Alone Frequency Counter: The AD654's output frequency can be connected to a stand-alone frequency counter or microcontroller to measure and display the frequency information accurately. This is useful in applications where frequency measurement is required.

LED Display Driver: The AD654 can be employed to drive LED displays. The frequency output can be used to control LED brightness or to create visual displays where LED intensity varies with the input voltage or signal.

AD654 VFC as an ADC: The AD654 can be used as the core of an analog-to-digital converter (ADC). By measuring the output frequency, you can digitize analog signals accurately. This approach is sometimes used in data acquisition systems.

Frequency Doubler: The AD654 can be configured to function as a frequency doubler, where the output frequency is twice the input frequency. This can be useful in applications that require frequency multiplication.

Analog to Digital Converter (ADC): As mentioned earlier, the AD654 can be used as part of an ADC circuit. It can convert analog signals into digital data by translating the input voltage into a corresponding frequency, which can then be digitized using a counter or microcontroller.

Equivalent Parts

Part Number Manufacturer Definition Typical Applications
TL494 Texas Instruments (TI) PWM Controller with VFC capability Power supplies, voltage regulation, motor control
MAX038 Maxim Integrated Precision high-frequency function generator IC Signal generation, waveform synthesis
LTC6905 Linear Technology (Now Part of Analog Devices) Precision oscillator with adjustable frequency range Frequency generation, clocking, signal generation
XR-2206 Exar (Now Part of MaxLinear) Monolithic function generator IC Frequency synthesis, waveform generation
ICL8038 Intersil (Now Part of Renesas Electronics Corp) Precision waveform generator/voltage-controlled oscillator IC
Function generation, frequency synthesis, waveform generation
MC1648 ON Semiconductor Oscillator circuit usable as a VFC or waveform generator Frequency generation, waveform synthesis
KA331 Fairchild Semiconductor (Now Part of ON Semi) Precision voltage-to-frequency converter Frequency measurement, signal conditioning
LM331 Texas Instruments (TI) Precision voltage-to-frequency converter
Frequency measurement, signal conditioning, instrumentation



Parameter Value Parameter Value
Manufacturer: Analog Devices Inc. Product Category: ADI
Brand: Analog Devices


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  • What is the pinout for AD654?

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  • What is the lifespan of AD654?

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