ICL7116 - 3½ Digit A/D Converter with LCD Driver

Overview

The Harris ICL7116 is a high-performance, low-power 3½ digit analog-to-digital (A/D) converter designed for precision measurement applications. It integrates a complete A/D conversion system, including a seven-segment decoder, display driver, voltage reference, and clock circuitry. The ICL7116 is specifically optimized for interfacing with liquid crystal displays (LCDs), featuring a multiplexed backplane drive to simplify display integration. Its sister component, the ICL7117, is designed for LED displays, making the ICL711x family versatile for various display requirements.

This component is widely used in instrumentation, handheld meters, and other applications requiring accurate digital readouts of analog signals. Its low power consumption and high integration reduce the need for external components, making it a cost-effective solution for compact designs.

Features

• HOLD Reading Input: Allows indefinite display hold for stable readings.
• Guaranteed Zero Reading: Ensures accurate 0V input representation.
• True Polarity at Zero: Enables precise null detection for differential measurements.
• Ultra-Low Input Current: Typically just 1pA, minimizing loading effects on measured signals.
• Direct Display Drive:
  • ICL7116: LCD interface with multiplexed backplane drive.
  • ICL7117: LED display driver (separate variant).
• Low Noise: Less than 15µV peak-to-peak (typical), ensuring stable readings.
• On-Chip Clock and Reference: Reduces external component count.
• Low Power Dissipation: Typically less than 10mW, ideal for battery-powered applications.
• No Additional Active Circuits Required: Fully self-contained A/D conversion system.
• Surface Mount Option: Available in a 44-lead metric quad flatpack (MQFP) for compact designs.

Applications

The ICL7116 is suited for a wide range of precision measurement applications, including:

• Digital panel meters
• Handheld multimeters
• Battery-powered instrumentation
• Process control systems
• Temperature measurement devices
• Scales and weighing systems
• Medical diagnostic equipment

Its ability to directly drive LCDs makes it particularly useful in portable and low-power devices where energy efficiency is critical.

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (V+ to V-): ±15V
• Analog Input Voltage: ±VDD
• Operating Temperature Range: 0°C to +70°C
• Storage Temperature Range: -65°C to +150°C

Key Performance Parameters

• Resolution: 3½ digits (1999 counts)
• Linearity Error: ±1 count maximum
• Zero Reading Error: 0V ± 0000 guaranteed
• Input Bias Current: 1pA (typical)
• Reference Voltage: On-chip, adjustable via external divider
• Conversion Rate: Typically 3 readings per second (adjustable via clock frequency)
• Power Consumption: <10mW (typical)

Package Information

Available Package Options

• ICL7116CPL: 40-lead Plastic Dual In-Line Package (PDIP)
• ICL7116CM44: 44-lead Metric Quad Flatpack (MQFP) – Surface Mount

Pin Configuration (40-Pin DIP)

The ICL7116 in PDIP form factor provides the following key pin functions:

• V+ and V-: Positive and negative supply rails (±5V typical)
• IN+ and IN-: Differential analog input pins
• REF HI/LO: Reference voltage input pins
• BP (Backplane): LCD backplane drive output
• SEG A-G: Seven-segment LCD driver outputs
• HOLD: Input to freeze the current display reading
• OSC1-OSC3: Clock oscillator connections

Functional Description

The ICL7116 employs a dual-slope integration technique for high-accuracy A/D conversion. This method provides excellent noise rejection, particularly for 50Hz/60Hz line interference. The conversion cycle consists of three phases:

1. Auto-Zero Phase: The input is disconnected, and internal offsets are nulled.
2. Signal Integrate Phase: The input voltage is integrated for a fixed time period.
3. Reference De-Integrate Phase: A known reference voltage is integrated in the opposite polarity until the integrator output returns to zero.

The time taken for the de-integration phase is proportional to the input voltage, providing the digital readout.

Design Considerations

Clock Frequency Selection

The conversion rate is determined by the clock frequency, typically set using an external RC network between OSC1, OSC2, and OSC3 pins. A 48kHz clock yields about 3 conversions per second – optimal for visual readability.

Reference Voltage Configuration

While the ICL7116 includes an internal reference, best accuracy is achieved by using a precision external reference. The reference voltage should be set to half of the full-scale input range (e.g., 1.000V for a 2.000V full-scale design).

LCD Interface

The multiplexed backplane drive (BP) must be connected to the common terminal of the LCD. Segment drivers (SEG A-G) connect to individual display segments. A contrast adjustment may be needed for optimal visibility.

Conclusion

The ICL7116 represents a complete, high-performance solution for 3½ digit A/D conversion with LCD drive capability. Its combination of precision, low power operation, and display integration makes it ideal for portable instruments and measurement systems where component count and power consumption are critical factors. The availability of both through-hole and surface mount packages provides flexibility for various product designs.