TC7135CPI

ADCs/DACs - Special Purpose Overview

The TC7135CPI is a 4-1/2 digit dual-slope integrating analog-to-digital converter (ADC) manufactured by Microchip Technology in a 28-pin PDIP package. It provides 50 ppm resolution with a maximum nonlinearity error of ±1 count and an auto-zero cycle that reduces zero error to below 10 µV. The device features multiplexed BCD data outputs, TTL-compatible logic levels, and control signals including BUSY, STROBE, and RUN/HOLD for microprocessor interfacing. Key electrical specifications include a typical input leakage current of 1 pA, a zero reading drift of 0.5 µV/°C, and operation with ±5V power supplies.

ADCs/DACs - Special Purpose Feature Summary

• Dual-slope integrating architecture with 4-1/2 digit resolution and ±1 count max nonlinearity error
• Multiplexed BCD digital outputs with TTL-compatible voltage levels for direct display or processor interface
• Auto-zero cycle reducing zero error to <10 µV and zero drift to 0.5 µV/°C
• Low input leakage current of 1 pA (max 10 pA) minimizing source impedance errors

ADCs/DACs - Special Purpose Applications

• Precision analog signal processing systems
• High accuracy DC measurement instrumentation
• Precision sensor interfaces requiring low drift
• Microprocessor-based data acquisition systems

ADCs/DACs - Special Purpose Procurement Notes

Verify the component matches the specific 28-pin PDIP package configuration. Confirm that the operating environment stays within the specified 0°C to +70°C temperature range. Ensure external reference components meet stability requirements for absolute accuracy measurements.

ADCs/DACs - Special Purpose Selection Notes

Select this component for applications requiring high precision DC measurements where low drift and noise immunity are critical. The dual-slope design offers inherent rejection of line frequency noise when clock frequencies are appropriately chosen. Consider the 1 pA input leakage for high-impedance source applications.

ADCs/DACs - Special Purpose Part Context

The TC7135 is part of Microchip's family of integrating A/D converters designed for high-accuracy measurement systems. The 'CPI' suffix denotes the commercial temperature range variant housed in a standard 28-pin plastic dual in-line package, distinguishing it from surface-mount MQFP or PLCC options.

ADCs/DACs - Special Purpose Replacement Considerations

Direct pin-for-pin replacements should be verified against the 28-pin PDIP footprint. Alternative ADCs must support dual-slope integration principles and compatible multiplexed BCD output timing to maintain existing circuit functionality without redesign.

ADCs/DACs - Special Purpose FAQ

How does the TC7135 handle overrange conditions?

If the input signal causes the reference voltage integration time to exceed 20,000 clock pulses, the OVERRANGE output goes high. In this state, all digit drive signals are held low, causing the display to blink visually.

What is the purpose of the ANALOG COMMON pin?

The ANALOG COMMON pin serves as the reference point for REF IN and the -INPUT return during auto-zero and de-integration phases. Tying it to the same point as -INPUT removes common-mode voltage from the converter.

How is the conversion rate determined?

The conversion rate depends on the clock frequency applied to the CLOCK IN pin. For example, a 120 kHz clock results in approximately 3 conversions per second, while a 100 kHz clock yields 2.5 conversions per second.