MAX3157CAI+

Overview

The MAX3157CAI+ 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. Drivers are short-circuit current limited and protected by thermal shutdown circuitry. The receiver input includes a fail-safe feature guaranteeing a logic high output if inputs are open, shorted, or connected to a terminated line with all drivers disabled.

Feature Summary

• Provides ±50V isolation using external capacitors for power transfer from the logic side to the isolated side.
• Features true fail-safe receiver operation while maintaining EIA/TIA-485 compliance.
• Includes thermal shutdown protection that places driver outputs into a high-impedance state during overload.
• Offers pin-selectable full/half-duplex operation and phase controls to correct for twisted-pair reversal.

Applications

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

Procurement Notes

Verify the specific suffix 'CAI+' against the manufacturer's official documentation to confirm the commercial temperature range (0°C to +70°C) and the 28-pin SSOP package configuration. Ensure compatibility with required isolation voltage levels and check for any obsolescence notices or lifecycle status updates directly from Analog Devices before finalizing procurement plans.

Selection Notes

Select this component when designing systems requiring galvanic isolation between logic and cable grounds without optocouplers. Consider the 250kbps maximum data rate and the need for external charge-pump capacitors (C1, C2) sized between 47nF and 100nF. Evaluate the requirement for independent phase control pins if twisted-pair wiring reversals are anticipated in the installation environment.

Part Context

The MAX3157 series serves as a low-cost replacement for traditional opto-isolated transceivers in RS-485 and RS-422 networks. The CAI variant specifically denotes the commercial temperature grade housed in a 28-pin Small Outline Package. This family integrates the isolation barrier directly within the hybrid microcircuit structure, simplifying board layout compared to discrete isolation solutions.

Replacement Considerations

Refer to the MAX1480 family data sheet for fully isolated RS-485/RS-422 transceiver alternatives. Verify pinout compatibility and electrical specifications against existing designs when considering cross-family replacements.

FAQ

How is the half-duplex mode selected on the MAX3157?

Half-duplex mode is selected by connecting the H/F pin to ISOVCC. 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 conditions?

Thermal shutdown circuitry protects the drivers against excessive power dissipation. When activated, it places the driver outputs into a high-impedance state.