Analog Devices Inc./Maxim Integrated MAX3140EEI+T

Overview

The MAX3140EEI+T from Maxim Integrated is a single-chip SPI/MICROWIRE-compatible UART with integrated true fail-safe RS-485/RS-422 transceiver in a 28-pin QSOP package. It delivers UART functionality (up to 230 kbaud, 8-word FIFO, 9-bit address recognition) and RS-485/RS-422 physical layer support (115 kbps / 500 kbps / 10 Mbps slew-rate programmable modes, ±13 V receiver input tolerance, 1/8-unit-load input impedance) for industrial serial communication systems requiring space, power, and I/O pin efficiency.

For engineers reviewing the MAX3140EEI+T datasheet, MAX3140EEI+T pinout, MAX3140EEI+T application, or MAX3140EEI+T equivalent, key selection considerations include its hardware/software compatibility with MAX3100 and MAX3089, independent transmitter/receiver phase control for twisted-pair polarity correction, true fail-safe receiver behavior under open/shorted bus conditions, and selectable half/full-duplex operation via H/F pin.

Technical Context

The MAX3140EEI+T integrates two functionally isolated blocks - a full-featured UART with crystal-derived oscillator and programmable baud-rate generator, and an RS-485/RS-422 transceiver with pin-programmable slew rate (SRL), duplex mode (H/F), and polarity inversion (TXP/RXP). These blocks share only VCC and GND, enabling independent use or coordinated operation.

Its UART supports SPI/QSPI/MICROWIRE timing (CPOL=0, CPHA=0), features an open-drain IRQ output with four maskable interrupt sources, and includes hardware handshaking (CTS/RTS). The transceiver implements thermal shutdown and short-circuit current limiting on driver outputs, with true fail-safe receiver logic guaranteeing RO = high when A–B is open or shorted.

Key Specifications

Pinout & Package

Package: 28-pin QSOP (0.154" wide), RoHS-compliant, lead-free.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar UART + RS-485 transceiver applications.

Compared with MAX3140CEI+, the MAX3140EEI+T extends operational reliability to harsher environments; compared with MAX3100EAP+, it eliminates external transceiver components and simplifies layout while retaining identical UART register mapping and SPI interface behavior.

Availability

MAX3140EEI+T is available at Aetrix Electronics and suitable for industrial automation, building management systems, and intelligent instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX3140EEI+T 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, automotive, and communications markets.

The MAX3140 product line integrates UART and RS-485/RS-422 functions into single packages to simplify serial interface design in space-constrained, noise-sensitive embedded systems.

FAQ

What is the maximum UART baud rate supported by the MAX3140EEI+T?

The MAX3140EEI+T supports UART data rates up to 230 kbaud when using a 3.6864 MHz crystal oscillator. This is achieved through software-programmable divider ratios in the baud-rate generator, covering standard rates from 300 baud to 230 kbaud. The actual achievable rate depends on crystal accuracy and system clock stability, but 230 kbaud is the documented maximum specified in the MAX3140EEI+T datasheet under typical conditions.

How does the true fail-safe feature of the MAX3140EEI+T work?

True fail-safe operation in the MAX3140EEI+T guarantees that the receiver output (RO) remains logic-high when the differential input (A–B) is open-circuited or shorted - specifically when A–B is ≥ –50 mV or ≤ –200 mV. This eliminates the need for external bias resistors on the RS-485 bus and prevents undefined states during cable faults or disconnections, directly enhancing system robustness in industrial deployments using MAX3140EEI+T.

Can the MAX3140EEI+T operate in both half-duplex and full-duplex RS-485 modes?

Yes, the MAX3140EEI+T supports both modes via the H/F pin: connect H/F to VCC for half-duplex (Y/Z used bidirectionally), or leave H/F unconnected or tied to GND for full-duplex (separate A/B inputs and Y/Z outputs). In full-duplex mode, the A/B inputs retain 1/8-unit-load impedance but do not affect RO output, allowing flexible network architecture without redesigning the MAX3140EEI+T interface.

What is the purpose of the TXP and RXP pins on the MAX3140EEI+T?

The TXP and RXP pins on the MAX3140EEI+T provide software-correctable polarity inversion: TXP = VCC inverts transmitter phase (Y/Z swap logic), and RXP = VCC inverts receiver phase (A/B interpretation). This allows field correction of twisted-pair wiring reversal without changing PCB layout or firmware - a key reliability feature confirmed in the MAX3140EEI+T functional description and pin tables.

Does the MAX3140EEI+T require an external crystal, or can it use an external clock?

The MAX3140EEI+T supports both configurations: X1 accepts either a 3.6864 MHz crystal (with X2 unconnected) or an external CMOS clock signal. When using a crystal, internal oscillator circuitry generates the UART clock; when using an external clock, X1 serves as the clock input and X2 is left floating. Both methods are fully supported and validated for MAX3140EEI+T operation across its full temperature range.