ICL7135CAI+

ADCs/DACs - Special Purpose Overview

The ICL7135CAI+ is a high-precision monolithic 4½ digit analog-to-digital converter (ADC) manufactured by Analog Devices/Maxim Integrated. It utilizes dual-slope conversion architecture to achieve ±1 count accuracy over a 20,000-count resolution with a 2.0000V full-scale capability. The device features true differential inputs, ratiometric operation, and auto-zero functionality with zero drift of 0.5µV/°C. It outputs multiplexed BCD data alongside status signals including BUSY, STROBE, OVERRANGE, and UNDERRANGE for microprocessor interfacing. Powered by +4V to +6V and -3V to -8V supplies, it operates within a commercial temperature range of 0°C to +70°C in an SSOP-28 package.

ADCs/DACs - Special Purpose Feature Summary

• 4½ Digit Resolution: Provides 20,000 counts with guaranteed ±1 count linearity error.
• Multiplexed BCD Interface: Outputs digit data sequentially with STROBE pulses for easy latching into external displays or microprocessors.
• High Precision Analog Performance: Features 10pA max input bias current, <10µV auto-zero accuracy, and true differential inputs ensuring zero reading at 0V input.
• Status Indicators: Includes active-high OVERRANGE and UNDERRANGE outputs for auto-ranging applications and POLARITY output for sign detection.

ADCs/DACs - Special Purpose Applications

• Digital Voltmeters (DVMs) and Panel Meters (DPMs)
• Microprocessor-based data acquisition systems
• Precision measurement of pressure, voltage, resistance, temperature, weight, current, speed, and material thickness

ADCs/DACs - Special Purpose Procurement Notes

Verify the specific suffix 'AI' against the manufacturer's official documentation to confirm pinout compatibility and package type, as ordering suffixes may indicate variations in packaging or testing specifications. Confirm availability through authorized distributors, as supply status can vary. Ensure the selected variant meets the required operating temperature range of 0°C to +70°C for the intended application environment.

ADCs/DACs - Special Purpose Selection Notes

Select external components carefully to optimize performance. Use polypropylene or Teflon integrating capacitors to minimize dielectric absorption errors. Choose a reference capacitor with low leakage to maintain scale factor stability during floating phases. Set the clock frequency to integer multiples of power line frequencies (e.g., 120kHz for 60Hz rejection) to maximize normal mode rejection. Ensure the integrating resistor value limits buffer output current between 5µA and 40µA for optimal linearity.

ADCs/DACs - Special Purpose Part Context

The ICL7135 is part of the Maxim Integrated ICL7135 series of 4½ digit A/D converters. It serves as a second-source equivalent to earlier Intersil designs, offering improved ESD protection and tighter test specifications without functional changes. The device is designed to interface directly with display drivers like the ICM7211A or connect to UARTs and microcontrollers via its multiplexed digital outputs.

ADCs/DACs - Special Purpose Replacement Considerations

The ICL7135 is functionally compatible with other 4½ digit dual-slope ADCs such as the ICL7106 or ICL7129, though pinouts and control logic may differ. Verify that any substitute supports multiplexed BCD outputs if direct replacement of the digital interface is required. Check that the alternative device offers similar input bias current and auto-zero capabilities to maintain system accuracy.