MAX3157EPI+

Overview

The MAX3157EPI+ is a high CMRR RS-485/RS-422 data-communications interface providing ±50V isolation in a hybrid microcircuit. It contains one transmitter and one receiver, operating at data rates up to 250kbps with a single +5V supply. The device features pin-selectable half- or full-duplex modes and independently programmable receiver and transmitter output phases. Supply current typically draws 25mA when unloaded and drops to 25µA in shutdown mode. It operates within a temperature range of -40°C to +85°C and is housed in a 28-pin PDIP package.

Feature Summary

• Provides ±50V isolation using external capacitors for power transfer from the logic side to the isolated side.
• Includes fail-safe circuitry that guarantees a logic-high receiver output when inputs are open, shorted, or terminated with drivers disabled.
• Features thermal shutdown protection that places driver outputs into a high-impedance state during excessive power dissipation.
• Supports phase control pins to correct for twisted-pair reversal without hardware changes.

Applications

• Industrial Controls
• Level Translators
• Telecommunications
• Local Area Networks

Procurement Notes

Verify component authenticity through authorized distributors or direct manufacturer channels. Confirm the specific E suffix indicates the extended temperature range (-40°C to +85°C) and the PI suffix denotes the 28-pin PDIP package. Check for RoHS compliance documentation and ensure the part status matches project requirements, as older components may have limited availability.

Selection Notes

Select this component when galvanic isolation between communication segments is required without using optocouplers. Ensure the application supports a single +5V supply and utilizes external charge-pump capacitors (typically 0.047µF) for the isolated side. Verify that the bus topology and termination resistors align with the specified input impedance options available via the YR, ZR, AR, and BR pins.

Part Context

This device belongs to the MAX3157 family of high CMRR RS-485 transceivers. The MAX3157EPI+ specifically designates the industrial temperature grade variant packaged in a 28-pin Plastic Dual In-Line Package. It serves as a low-cost replacement for traditional opto-isolated transceivers while maintaining EIA/TIA-485 compliance.

Replacement Considerations

For fully isolated RS-485/RS-422 transceivers, refer to the MAX1480 family datasheet. Other variants in the same series include the MAX3157CAI (commercial temp, SSOP), MAX3157EAI (extended temp, SSOP), and MAX3157CPI (commercial temp, PDIP).

FAQ

How is the half-duplex mode selected?

Connect the H/F pin to ISOVCC to select half-duplex operation. Connecting it to ISOCOM selects full-duplex mode.

What happens if the receiver inputs are left open?

The fail-safe feature guarantees a logic-high receiver output if the inputs are open, shorted, or connected to a terminated transmission line with all drivers disabled.

How does the device handle driver overload?

Thermal shutdown circuitry protects the drivers against excessive power dissipation by placing the driver outputs into a high-impedance state if the die temperature becomes too high.