MAX3157CPI+

Overview

The MAX3157CPI+ 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. The device uses a single +5V supply on the logic side, with external ±50V capacitors transferring power to the isolated side. It features short-circuit current limiting and thermal shutdown protection. Supply current is typically 25mA when unloaded and drops to 25µA in shutdown mode. The component operates within a temperature range of 0°C to +70°C and is housed in a 28-pin PDIP package.

Feature Summary

• Provides ±50V isolation for RS-485/RS-422 communication using a single +5V logic supply.
• Features pin-selectable half-duplex or full-duplex operation modes.
• Includes independently programmable receiver and transmitter output phase pins to correct twisted-pair reversal.
• Integrates fail-safe circuitry that guarantees a logic-high receiver output when inputs are open or shorted.

Applications

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

Procurement Notes

Verify the specific suffix 'CPI+' against the manufacturer's official documentation to confirm the 28-pin PDIP package and commercial temperature range (0°C to +70°C). Confirm RoHS compliance status as indicated in the datasheet. Check for obsolescence notices, as this component family has been subject to end-of-life notifications by Analog Devices/Maxim Integrated.

Selection Notes

Select this component for applications requiring galvanic isolation between logic and cable grounds without separate isolated power supplies. Ensure the system design accommodates the required charge-pump capacitors (C1, C2) for voltage transfer. Verify that the 250kbps maximum data rate meets the network requirements. Consider the thermal shutdown feature for environments prone to driver overload conditions.

Part Context

The MAX3157 series serves as a low-cost replacement for opto-isolated transceivers in RS-485/RS-422 networks. The 'C' designation indicates the commercial temperature grade, while 'P' denotes the plastic dual in-line package. This part belongs to the broader MAX3157 family, which also includes SSOP variants and extended temperature versions.

Replacement Considerations

Public confirmed substitute part numbers include MAX3157CAI, MAX3157EAI, MAX3157EPI, and MAX3157CAI+. Verify pin compatibility and electrical specifications before substitution.

FAQ

How is the half-duplex mode selected?

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?

Drivers are protected by short-circuit current limiting and thermal shutdown circuitry. If the die temperature becomes excessive, the thermal shutdown forces the driver outputs into a high-impedance state.