ADC0801 - 8-Bit Successive Approximation ADC

Overview

The ADC0801, ADC0802, ADC0803, ADC0804, and ADC0805 are a family of CMOS 8-bit successive approximation analog-to-digital converters (ADCs) that utilize a differential potentiometric ladder architecture. These converters are specifically designed for seamless operation with NSC800 and INS8080A derivative control buses, featuring TRI-STATE output latches that directly interface with data buses. The ADC0801 series appears to microprocessors as memory locations or I/O ports, eliminating the need for additional interfacing logic.

Key Features

• 8-bit resolution with 1 LSB accuracy
• Compatible with 8080 microprocessor derivatives - no interfacing logic required
• Differential analog voltage inputs
• On-chip clock generator (only external RC required)
• 0V to 5V analog input voltage range with single 5V power supply
• TRI-STATE output latches directly drive data bus
• Conversion time of 100μs
• Low power consumption - 15mW typical
• Operates with 2.5V (LM336) voltage reference
• No zero or full-scale adjust required
• Standard 20-pin DIP or PLCC package

Applications

The ADC0801 series is suitable for a wide range of applications including:

• Microprocessor-based systems
• Process control
• Instrumentation systems
• Remote data acquisition
• Analog-to-digital conversion in embedded systems
• Data logging systems
• Industrial control systems
• Automotive sensor interfaces
• Consumer electronics

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (VCC): 6.5V
• Control Input Voltage: -0.3V to VCC +0.3V
• Analog Input Voltage: -0.3V to VCC +0.3V
• Operating Temperature Range: 0°C to +70°C
• Storage Temperature Range: -65°C to +150°C

DC Characteristics (VCC = 5V, TA = 25°C unless otherwise specified)

• Resolution: 8 bits
• Total Unadjusted Error: ±1/2 LSB max
• Zero Error: ±1 LSB max
• Full Scale Error: ±1 LSB max
• Power Supply Sensitivity: ±0.1%/% of VCC
• Analog Input Current: 1μA max
• Power Consumption: 15mW typical

AC Characteristics

• Conversion Time: 100μs max
• Clock Frequency: 640kHz typical (with RC = 10kΩ, 150pF)
• Access Time: 135ns max
• Data Hold Time: 20ns min
• Output Enable to Data Valid: 100ns max

Functional Description

The ADC0801 utilizes successive approximation technique to convert analog signals to digital values. The device contains an internal clock generator which only requires an external resistor and capacitor to set the frequency. The analog input is differential, allowing for the measurement of small signals superimposed on large common-mode voltages.

The conversion process is initiated by a start pulse (active low). The end of conversion is signaled by the INTR output (active low). The digital result can then be read from the TRI-STATE output latches. The device includes an internal 256R resistor ladder network that performs the digital-to-analog conversion function.

Package Information

20-Pin DIP Package

• Package Type: PDIP (Plastic Dual In-line Package)
• Package Code: N
• Lead Count: 20
• Body Width: 0.3 inch
• Body Length: 1.0 inch
• Lead Pitch: 0.1 inch
• Operating Temperature: 0°C to +70°C

20-Pin PLCC Package

• Package Type: PLCC (Plastic Leaded Chip Carrier)
• Package Code: FN
• Lead Count: 20
• Body Size: 0.35 x 0.35 inch
• Lead Pitch: 0.05 inch
• Operating Temperature: 0°C to +70°C

Pin Configuration and Description

Pinout (20-Pin DIP)

• Pin 1: CS (Chip Select) - Active low input
• Pin 2: RD (Read) - Active low input
• Pin 3: WR (Write) - Active low input
• Pin 4: CLK IN (Clock Input)
• Pin 5: INTR (Interrupt) - Active low output
• Pin 6: VIN(+) - Positive analog input
• Pin 7: VIN(-) - Negative analog input
• Pin 8: AGND - Analog ground
• Pin 9: VREF/2 - Reference voltage input
• Pin 10: DGND - Digital ground
• Pins 11-18: DB0-DB7 - Data bus lines (TRI-STATE)
• Pin 19: CLK R - Clock connection for RC network
• Pin 20: VCC - +5V power supply

Typical Application Circuit

A typical application circuit for the ADC0801 includes:

• 5V power supply connected to VCC (pin 20)
• Analog and digital grounds connected to system ground
• RC network (typically 10kΩ resistor and 150pF capacitor) between CLK IN (pin 4) and CLK R (pin 19)
• Reference voltage of 2.5V applied to VREF/2 (pin 9) for full 0-5V input range
• Analog input signal applied differentially between VIN(+) (pin 6) and VIN(-) (pin 7)
• Control signals (CS, RD, WR) connected to microprocessor control bus
• Data outputs (DB0-DB7) connected to microprocessor data bus
• INTR output (pin 5) can be connected to microprocessor interrupt input

Design Considerations

When designing with the ADC0801, consider the following:

• Proper grounding techniques are essential - keep analog and digital grounds separate and connect at a single point
• The reference voltage determines the input range - for 0-5V input, use 2.5V at VREF/2
• Bypass capacitors (0.1μF) should be placed close to VCC and ground pins
• The RC network for the clock should use stable components to maintain consistent conversion timing
• For noisy environments, consider adding filtering on the analog inputs
• The conversion time of 100μ