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AD573 in Practice: Legacy Tradeoffs, Dual-Rail Power, and Modern Fixes

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Quick-Reference Card: AD573 at a Glance

Attribute Detail
Component Type 10-bit Successive Approximation ADC
Manufacturer Analog Devices, Inc.
Key Spec 20 μs Typical Conversion Time
Supply Voltage +5V and -12V to -15V (Dual Rail)
Package Options 20-pin DIP, 20-pin PLCC
Lifecycle Status Obsolete / Discontinued
Best For Legacy industrial data acquisition and 8-bit/16-bit microprocessor interfacing

AD573 20-pin DIP package photo showing the Analog Devices branding


1. What Is the AD573? (Definition + Architecture)

The AD573 is a complete 10-bit successive approximation analog-to-digital converter (ADC) from Analog Devices, Inc. that integrates a DAC, voltage reference, clock, and three-state buffers onto a single monolithic chip. Unlike modern ADCs that often require external voltage references or precision clocks, the AD573 was designed as a "set-and-forget" solution for the parallel bus era.

1.1 Core Architecture & Design Philosophy

The AD573 utilizes a Successive Approximation Register (SAR) architecture. Internally, it uses a high-speed DAC and a comparator to test each bit of the digital output against the analog input. Because the clock is integrated, the timing is handled internally once the "Convert" signal is pulsed. This design choice was intended to simplify the interface for engineers working with Z80, 8080, or early 68000-series processors, where external timing components would have consumed precious PCB real estate.

1.2 Where It Fits in the Signal Chain / Power Path

In a typical system, the AD573 acts as the bridge between high-level analog signals (like 0-10V industrial sensors) and a parallel data bus. It is positioned downstream from an operational amplifier or buffer and upstream from a microcontroller or microprocessor's data port.


2. Electrical Characteristics: The Numbers That Matter

2.1 Power Supply & Consumption Profile

The AD573 is a product of its time, requiring dual power supplies: a +5V digital rail and a negative analog rail ranging from -12V to -15V. - So What? This makes the AD573 difficult to integrate into modern 3.3V single-supply systems without adding a dedicated negative voltage regulator or a charge pump, increasing BOM complexity.

2.2 Performance Specs (Speed and Accuracy)

  • Resolution: 10-bit (1024 levels).
  • Conversion Time: 20 μs (typical).
  • So What? While 20 μs was fast for the 1980s, modern SAR ADCs like the AD7980 can achieve 1 MSPS (1 μs), making the AD573 unsuitable for high-speed signal processing but adequate for slow-moving industrial telemetry.

2.3 Absolute Maximum Ratings — What Will Kill It

Parameter Rating
VCC to Digital Common 0V to +7V
VEE to Digital Common 0V to -16.5V
Analog Input to Analog Common ±25V

Note: Reversing the polarity of the VEE supply or exceeding -16.5V will likely result in immediate latch-up and permanent silicon failure.


3. Pinout & Package Guide

3.1 Pin-by-Pin Functional Groups

Pin Group Pins Function
Power VCC, VEE, DGND, AGND Supply rails and ground references
Analog Input VIN, BIPOFF Analog signal input and bipolar offset control
Digital Output DB0-DB9 10-bit parallel data output
Control DR, STS, CE Data Ready, Status, and Chip Enable signals

3.2 Package Variants & Soldering Notes

Package Pitch Thermal Pad? Soldering Method
20-pin DIP 100 mil No Wave / Hand Solder
20-pin PLCC 50 mil No Reflow / J-Lead

The 20-pin DIP is ideal for through-hole repair work, while the PLCC version was the standard for surface-mount designs before the industry shifted to SOIC and QFN packages.

3.3 Part Number Decoder

A typical part number like AD573JN breaks down as: - AD573: Base model number. - J/K/S: Accuracy grade (K is usually higher precision over temperature). - N/D/P: Package code (N = Plastic DIP, D = Ceramic DIP, P = PLCC).


4. Known Issues, Errata & Real-World Pain Points

4.1 Obsolescence & Sourcing

Problem: The AD573 is officially discontinued. Root Cause: The shift toward serial interfaces (SPI/I2C) and single-supply low-voltage operation rendered parallel, dual-rail ADCs obsolete. Recommended Fix: For new designs, migrate to the AD1674 (if parallel is required) or the AD7980 (for modern SPI-based designs).

4.2 Complex Power Sequencing

Problem: The requirement for a -12V to -15V rail. Root Cause: The internal comparator and DAC architecture require a negative headroom to process bipolar signals. Recommended Fix: If you must maintain the AD573 in a legacy system, use a DC-DC inverter like the ICL7660 to generate the negative rail from a standard +5V supply.


5. Application Circuits & Integration Examples

5.1 Typical Application: Industrial Data Acquisition

The AD573 is frequently used to monitor 0V to +10V signals. By connecting the BIPOFF pin correctly, the device can be toggled between unipolar (0 to 10V) and bipolar (-5V to +5V) input ranges.

AD573 typical application circuit schematic for 0-10V unipolar input

5.2 Interface Example: Connecting to a Microcontroller

To interface with a modern MCU, the 10-bit parallel output must be mapped to two 8-bit GPIO ports. The STS (Status) pin should be monitored to detect the end of a conversion.

// Pseudocode for AD573 Data Read
start_conversion();        // Pulse Convert line
while(read_STS() == HIGH); // Wait for conversion to complete
data_low = read_PORTA();   // Read first 8 bits
data_high = read_PORTB();  // Read remaining 2 bits

6. Alternatives, Replacements & Cross-Reference

6.1 Pin-Compatible & Functional Replacements

Part Number Manufacturer Key Difference Compatible?
AD1674 Analog Devices 12-bit resolution, faster ?? (Check Pinout)
TLC1543 Texas Instruments Serial interface (SPI) ? (Redesign req)
AD7812 Analog Devices 10-bit, serial, single supply ? (Redesign req)

6.2 Upgrade Path

If you are designing a next-gen product, move away from parallel ADCs. The AD7980 offers 16-bit resolution in a tiny MSOP package and operates on a single supply, drastically reducing PCB footprint and power consumption.


7. Procurement & Supply Chain Intelligence

  • Lifecycle Status: Obsolete. No longer in active production.
  • Typical MOQ: N/A (Available primarily through independent distributors or "New Old Stock" brokers).
  • BOM Risk Factors: High. Sourcing genuine AD573 parts in 2024 carries the risk of counterfeit or reclaimed components.
  • Authorized Distributors: Consult authorized Analog Devices distributors (e.g., Arrow, Mouser, DigiKey) for remaining inventory or recommended modern alternatives.

8. Frequently Asked Questions

Q: What is the AD573 used for? The AD573 is primarily used for legacy microprocessor interfacing in industrial measurement and control systems, as well as older aerospace and defense equipment.

Q: What are the best alternatives to the AD573? The AD1674 is a common parallel-bus upgrade, while the Texas Instruments TLC1541/1543 series offers similar 10-bit performance in a different interface format.

Q: Is the AD573 still in production? No, the AD573 is discontinued. It is recommended only for maintenance of existing legacy hardware.

Q: Can the AD573 work with 3.3V logic? The AD573 is designed for 5V TTL logic. Interfacing with 3.3V MCUs requires level shifters to prevent damaging the microcontroller's GPIO pins.


9. Resources & Tools

  • Official Datasheet: [Analog Devices, Inc. AD573 Product Page]
  • Reference Designs: See Analog Devices App Note AN-282 for SAR ADC grounding techniques.
  • SPICE Model: Refer to the Analog Devices website for legacy macromodels.

AD573KN Documents & Media

Download datasheets and manufacturer documentation for Analog Devices, Inc. AD573KN.

AD573KN PCB Symbol, Footprint & 3D Model

Analog Devices, Inc. AD573KN

Analog Devices, Inc.

ADC Single SAR 10-bit Parallel 20-Pin PDIP N

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