Analog Devices Inc./Maxim Integrated MAX135CPI+

Overview

MAX135CPI+ from Maxim Integrated is a 16-bit, dual-slope analog-to-digital converter (ADC) with internal reference and serial interface, operating at ±5V supply, achieving 0.0015% integral nonlinearity (INL), and supporting 10–15 samples per second for precision measurement in industrial process control systems.

For engineers reviewing the MAX135CPI+ datasheet, MAX135CPI+ pinout, MAX135CPI+ application, or MAX135CPI+ equivalent, key selection considerations include its dual-slope architecture for noise immunity, integrated 4.096V reference, serial 3-wire interface timing, and 28-pin DIP package thermal and layout constraints.

Technical Context

The MAX135CPI+ implements a dual-slope integration ADC architecture with auto-zeroing and internal 4.096V bandgap reference, enabling high-accuracy DC measurements. It uses a 22-bit internal counter and supports programmable integration time (10–200ms) to optimize resolution versus conversion speed trade-offs.

Its serial interface operates with three dedicated lines (CS, CLK, DATA) and requires external clock input up to 2.5MHz; no parallel bus or microcontroller-specific protocol is used. The device performs self-calibration on power-up and supports system calibration via external reference.

Key Specifications

Pinout & Package

MAX135CPI+ is housed in a 28-pin plastic DIP (Dual In-line Package) with 0.6-inch body width and through-hole mounting. Pin spacing is 0.1 inch; lead finish is tin-lead.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar precision dual-slope ADC applications.

Compared with AD7715ARZ and LTC1446CN, the MAX135CPI+ uniquely integrates both dual-slope noise rejection and a trimmed 4.096V reference in a through-hole DIP package-critical for legacy test equipment redesigns and calibration-grade instruments where layout simplicity and long-term drift stability are prioritized over throughput.

Availability

MAX135CPI+ is available at Aetrix Electronics and suitable for digital panel meters, benchtop multimeters, and calibration standards requiring stable component supply and long-lifecycle support.

Supply support for MAX135CPI+ includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) designs precision analog, mixed-signal, and power management ICs for industrial, medical, and communications applications.

The MAX135CPI+ belongs to Maxim's precision ADC product line, engineered specifically for high-stability, low-drift DC measurement systems where dual-slope architecture and internal reference integrity are mandatory.

FAQ

What is the maximum sample rate of the MAX135CPI+?

The MAX135CPI+ achieves a fixed conversion rate of 10–15 samples per second due to its dual-slope integration architecture. This rate is determined by internal timing and cannot be increased via external clock scaling or configuration registers. Each conversion includes auto-zero and integration phases, limiting throughput but ensuring high noise immunity-making the MAX135CPI+ ideal for stable DC measurements rather than dynamic signal capture.

Does the MAX135CPI+ require an external reference?

No, the MAX135CPI+ includes a factory-trimmed 4.096V internal bandgap reference with ±25ppm/°C temperature drift. This eliminates the need for external reference components in most applications. However, the device also supports external reference input via the REFIN pin, allowing substitution with a higher-precision or temperature-compensated reference if required for metrology-grade use cases involving the MAX135CPI+.

Is the MAX135CPI+ pin-compatible with other Maxim ADCs like the MAX134?

No, the MAX135CPI+ is not pin-compatible with the MAX134 or other members of the MAX13x family. Its 28-pin DIP footprint, signal assignment (e.g., dedicated CAL, RANGE, ZERO pins), and serial interface implementation differ significantly. Board-level replacement requires schematic and layout revision. Always verify pin functions against the official MAX135CPI+ datasheet before integration.

What supply voltages does the MAX135CPI+ require?

The MAX135CPI+ requires dual ±5V analog supplies (V_DD = +5V, V_SS = −5V) and does not support single-supply operation. Digital I/O levels are referenced to V_DD and ground, and all control pins (CS, CLK, CAL, etc.) accept TTL/CMOS-compatible logic thresholds. Decoupling capacitors (0.1µF ceramic) must be placed adjacent to pins 1 and 28 to ensure stable operation of the MAX135CPI+.

Can the MAX135CPI+ perform self-calibration?

Yes, the MAX135CPI+ performs automatic zero calibration on power-up and supports both auto-zero and full-system calibration modes. System calibration uses an external reference applied to the REFIN pin and adjusts internal DACs to correct gain and offset errors. These calibration routines are initiated via hardware control pins (CAL, ZERO, RANGE) and do not require firmware-enabling reliable accuracy maintenance in the MAX135CPI+ across temperature and aging without host processor intervention.