ICL7135CQI+T

ADCs/DACs - Special Purpose Overview

The ICL7135CQI+T is a monolithic 4½-digit analog-to-digital converter (ADC) utilizing dual-slope integration architecture. It provides ±20,000 count resolution with guaranteed ±1 count accuracy and a 2.0000V full-scale capability. The device features high-impedance differential inputs, true ratiometric operation, and auto-zero functionality achieving better than 10µV accuracy. Key electrical parameters include a maximum input bias current of 10pA, zero drift of 0.5µV/°C, and rollover error under 1 count. It operates on +5V and -5V supplies with a typical supply current of 3.0mA per rail at 25°C. The component outputs multiplexed BCD data via TTL-compatible digital interfaces.

ADCs/DACs - Special Purpose Feature Summary

• Dual-slope conversion architecture with ±20,000 count resolution and ±1 count linearity accuracy.
• High-precision analog performance including 10pA max input bias current and <10µV auto-zero offset.
• Multiplexed BCD outputs with STROBE, BUSY, OVERRANGE, UNDERRANGE, and POLARITY status signals for microprocessor interfacing.
• True differential input configuration ensuring zero reading guarantee for 0V input and precise null detection.

ADCs/DACs - Special Purpose Applications

• Precision Digital Voltmeters (DVMs) and Digital Panel Meters (DPMs)
• Microprocessor-based data acquisition and control systems
• Industrial measurement instruments requiring ratiometric voltage sensing

ADCs/DACs - Special Purpose Procurement Notes

Verify the 'CQI' suffix indicates the 28-lead Plastic Chip Carrier package variant. Confirm the '+T' suffix corresponds to tape-and-reel packaging if required by assembly equipment. Ensure the source document explicitly defines these suffixes, as distributor listings may vary in nomenclature interpretation. Cross-reference the manufacturer's official ordering guide to validate the specific package and reel configuration before procurement.

ADCs/DACs - Special Purpose Selection Notes

Select this component when a high-resolution, low-noise ADC with direct LCD or LED driver interface is required. The ICL7135 eliminates external logic for BCD decoding but requires external integrating capacitors with low dielectric absorption (e.g., polypropylene) and a stable reference voltage. It is suitable for applications demanding true ratiometric measurements and robust common-mode rejection without complex digital signal processing overhead.

ADCs/DACs - Special Purpose Part Context

The ICL7135 is part of the Maxim Integrated family of precision A/D converters, succeeding earlier Intersil designs. It serves as a second-source equivalent to the ICL7135CQI, offering upgraded quality levels and tighter test specifications over temperature ranges. The device bridges the gap between simple comparator circuits and complex sigma-delta converters, providing a cost-effective solution for static DC voltage measurement tasks.

ADCs/DACs - Special Purpose Replacement Considerations

Public confirmed substitute part numbers: ICL7135CQI (standard plastic chip carrier variant). Verify pinout compatibility and electrical characteristics against the original datasheet before substitution.

ADCs/DACs - Special Purpose FAQ

How does the ICL7135 handle over-range conditions?

When the input exceeds the full-scale range, the OVERRANGE output goes high. The digit scan stops after the strobe sequence and remains stopped until the start of the de-integrate phase, causing the display to flash as an over-range indicator.

What is the recommended clock frequency for power line noise rejection?

For 60Hz rejection, frequencies like 120kHz (3 readings/sec) are common. For 50Hz rejection, 100kHz (2.5 readings/sec) is effective. The signal integration period should be an integral multiple of the power line cycle for maximum normal mode rejection.

Why is the choice of integrating capacitor critical for this device?

The integrating capacitor must have low dielectric absorption to minimize integral nonlinearity, rollover errors, and ratiometric errors. Polypropylene or Teflon capacitors are typically recommended to ensure accurate conversion results.