AD654JN Description

The AD654JN is a monolithic voltage-to-frequency (V/F) converter with an input amplifier, precision oscillator, and high-current output stage. It supports input voltages up to ±30 V and full-scale frequencies up to 500 kHz with a single RC network, offering 0.03% linearity error at 250 kHz and an 80 dB dynamic range. Operating from 5–36 V with only 2 mA quiescent current, it is accurate and efficient for industrial applications.

Its low-drift input amplifier (4 µV/°C typ) and high input resistance (250 MΩ) allow direct use with small signals like thermocouples or strain gauges. The AD654JN provides a square-wave output capable of driving up to 12 TTL loads, optocouplers, or long cables.

AD654JN Key Specs

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AD654JN Pinout

Pin 1 – Fout:

This pin provides the square-wave frequency output. The output frequency is proportional to the input voltage applied to the converter.

Pin 2 – Logic Common:

This pin serves as the logic ground reference and is typically connected to the system ground.

Pin 3 – RT:

This pin connects to an external resistor used to set or adjust the output frequency range of the converter.

Pin 4 – +Vin:

This is the analog voltage input pin where the input signal is applied for voltage-to-frequency conversion.

Pin 5 – −VS:

This pin is the negative supply voltage input when using a dual-polarity power supply.

Pin 6 – CT:

This pin connects to an averaging capacitor that helps stabilize the oscillator and smooth the conversion process.

Pin 7 – CT:

This is an additional capacitor connection used together with Pin 6 to improve filtering and frequency stability.

Pin 8 – +VS:

This pin is the positive supply voltage input and connects to the main power supply (Vcc).

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AD654JN Features

Low Cost

Single or Dual Supply, 5 V to 36 V, 65 V to 618 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

AD654JN Highlights

l  Compact Package Options: Available in 8-lead mini-DIP and SOIC packages, requiring only an RC timing network and pull-up resistor to configure the full-scale frequency.

l  Simple External Components: A single RC network can set full-scale frequencies up to 500 kHz and input ranges up to ±30 V.

l  Wide Application Use: Suitable for applications such as A/D conversion, signal transmission, F/V conversion, PLL circuits, and switched-capacitor filters.

l  Low Power Operation: Operates from 4.5 V to 36 V with only 2 mA quiescent current, supporting both positive and negative input signals.

l  Flexible Open-Collector Output: Can sink over 10 mA and easily interface with various logic families using different logic levels.

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AD654JN Functional Block Diagram

AD654 core operating principle involves the input voltage at VIN (Pin 4) being processed by an internal high-impedance operational amplifier to create a proportional current through an external resistor RT at Pin 3. This current then drives the internal precision oscillator (OSC), which performs charging and discharging via an external capacitor CT connected between Pins 6 and 7.

The output stage consists of a DRIVER controlling an open-collector transistor, which converts the oscillation into a frequency output at FOUT (Pin 1). Pin 2 (LOGIC COMMON) allows for flexible setting of the output logic level, making it easily compatible with TTL, CMOS, or other digital circuits. In essence, it accurately and linearly converts an analog voltage into a pulse frequency through a simple combination of RT and CT.

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AD654JN Applications

1. Analog-to-Digital Conversion (A/D Conversion)

The AD654JN converts analog voltage signals into proportional frequency outputs, allowing microcontrollers or digital counters to easily measure analog data by counting pulses.

2. Isolated Signal Transmission

In industrial environments, analog signals can be converted to frequency signals and transmitted over long cables or through optocouplers, improving noise immunity and maintaining signal accuracy.

3. Frequency-to-Voltage (F/V) Conversion Systems

The device can be used with F/V converters to form complete signal processing systems, enabling accurate frequency-to-voltage transformations in measurement and control circuits.

4. Phase-Locked Loop (PLL) Circuits

The AD654JN provides stable frequency outputs that can be integrated into PLL systems for synchronization, frequency control, and signal modulation applications.

5. Switched-Capacitor Filter Tuning

Its frequency output can be used to control or tune switched-capacitor filters, allowing precise adjustment of filter characteristics in signal processing circuits.

6. Sensor Signal Conditioning

Thanks to its high input impedance and low drift amplifier, the AD654JN can directly interface with low-level sensors such as thermocouples, strain gauges, and other precision sensing elements.

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Outline Dimensions

When designing and integrating the AD654 circuit, understanding its outline dimensions is essential. The package size, pin spacing, and overall structure can directly affect PCB layout and mounting design.

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