STMicroelectronics ST4E1240DT

Overview

ST4E1240DT from STMicroelectronics is a high-speed, half-duplex RS-485 transceiver in SO-8 package, operating from 3 V to 5.5 V supply, delivering 40 Mbps data rate, ±12 kV IEC61000-4-2 contact ESD protection on bus pins A/B, and fail-safe receiver behavior for open/shorted/idle bus conditions. It enables robust industrial serial communication in factory automation, motion control, and smart metering systems.

For engineers reviewing the ST4E1240DT datasheet, ST4E1240DT pinout, ST4E1240DT application, or ST4E1240DT equivalent, key selection criteria include differential output voltage ≥2.1 V at 5 V (PROFIBUS-compliant), thermal shutdown at 165 °C, hot-swap capability up to 100 pF parasitic capacitance, and guaranteed operation from –40 °C to +85 °C in SO-8.

Technical Context

The ST4E1240DT implements a true half-duplex RS-485 interface with independent driver enable (DE, active-high) and receiver enable (RE, active-low) controls, supporting up to 64 nodes on a single bus. Its fail-safe receiver asserts logic-high output under open, shorted, or idle bus conditions via internal threshold hysteresis (VTH+ = –10 mV typ., VTH– = –130 mV typ.) and >24 kΩ input impedance.

Driver switching performance is characterized by 0.5–7.5 ns rise/fall times (RL = 54 Ω, CL = 50 pF), 4–20 ns propagation delay, and pulse skew ≤3 ns. Thermal shutdown activates at 165 °C with 13 °C hysteresis, and shutdown current is ≤3.5 µA at all temperatures and supply voltages.

Key Specifications

Pinout & Package

ST4E1240DT is housed in an industry-standard SO-8 package (8-pin small outline integrated circuit) with gull-wing leads, JEDEC MS-012AC compliant, 1.27 mm pitch, and exposed pad not present (DFN8 variant has EP; SO-8 does not).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX13487EESA+, ST4E1240DT adds thermal shutdown and fail-safe operation without external components; versus SN65HVD256DR, it doubles data rate at the cost of fixed-fast slew rate - favoring timing-critical over EMI-sensitive deployments.

Availability

ST4E1240DT is available at Aetrix Electronics and suitable for factory automation, motion control, and smart metering applications requiring stable component supply, long-term industrial qualification, and guaranteed SO-8 packaging consistency.

Supply support for ST4E1240DT 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing microcontrollers, analog ICs, power devices, and sensors for industrial, automotive, and consumer markets.

The ST4E series targets industrial RS-485 communication, emphasizing robustness, wide supply range, and fail-safe operation for harsh electromagnetic and thermal environments in automation infrastructure.

FAQ

What is the maximum cable length supported by ST4E1240DT at 40 Mbps?

At 40 Mbps, ST4E1240DT supports up to 10 m of standard 120 Ω twisted-pair cable (e.g., Belden 9841) with proper termination. Longer runs require reduced data rates: 300 m is achievable at 16 Mbps (per ST4E1216), and 80 m at 16 Mbps per Figure 43 in DS14542. Signal integrity depends on stub length, termination quality, and noise coupling - not solely on transceiver specs.

Does ST4E1240DT require external bias resistors for fail-safe operation?

No. ST4E1240DT integrates a fail-safe receiver that actively drives R output high during open, shorted, or idle bus conditions without external resistors. This is achieved via internal comparator thresholds (VTH+ ≈ –10 mV, VTH– ≈ –130 mV) and hysteresis (30 mV), eliminating design overhead and board space for pull-up/pull-down networks.

How does hot-swap capability work on ST4E1240DT?

Hot-swap capability is enabled by internal weak pull-down on DE and pull-up on RE, combined with controlled input stage design that tolerates up to 100 pF of parasitic capacitance during plug-in. This prevents metastability or unintended bus drive during power sequencing, allowing safe insertion into live RS-485 networks without disrupting ongoing communication.

Can ST4E1240DT operate with a 3.3 V supply while maintaining 40 Mbps performance?

Yes. ST4E1240DT is fully specified from 3.0 V to 5.5 V, and its 40 Mbps rating applies across this full range. At 3.3 V, differential output voltage remains ≥1.5 V (Table 8), rise/fall times stay within 0.5–7.5 ns (Figure 27), and propagation delay is ≤16 ns (Figure 28), ensuring timing compliance in mixed-voltage industrial systems.