Maxim's MAX31911/MAX31913 industrial interface serializer translates, conditions, and serializes the 24 V digital output of sensors and switches used in industrial, process, and building automation to 5 V CMOS-compatible signals required by microcontrollers. It provides the front-end interface circuit of a programmable logic controller (PLC) digital input module.
The device features integrated current limiting, lowpass filtering, and channel serialization. Input current limiting allows a significant reduction in power consumed from the field voltage supply as compared to traditional discrete resistor-divider implementations. Selectable on-chip lowpass filters allow flexible debouncing and filtering of sensor outputs based on the application. On-chip serialization allows a drastic reduction in the number of optocouplers used for isolation.
The device serializer is stackable so that any number of input channels can be serialized and output is through only one SPI-compatible port. This reduces the number of optocouplers needed to only three, regardless of the number of input channels. For enhanced robustness with respect to high-frequency noise and fast electrical transients, a multi-bit CRC code is generated and transmitted through the SPI port for each 8 bits of data. The on-chip 5 V voltage regulator can be used to power external optocouplers, digital isolators, or other external 5 V circuitry.
Note: The MAX31913 is a successor to the MAX31911 and it adds new features including integrated field-side energyless LED drivers and dual-supply voltage monitors.
The MAX31912 uses patent-pending circuit techniques to achieve further reduction of power beyond what is possible by input current limiting alone. For low-cost applications, Maxim Integrated offers a pin compatible version of this device, the MAX31913, which does not include the patent-pending current-switching circuitry included in the MAX31912.