For new designs, please refer to MAX22190 ›
The MAX31912 industrial interface serializer translates,
conditions, and serializes the 24V digital output of sensors
and switches used in industrial, process, and building
automation to 5V 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 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 multibit CRC code is
generated and transmitted through the SPI port for each
8 bits of data. The on-chip 5V voltage regulator can be
used to power external optocouplers, digital isolators, or
other external 5V circuitry. Field-side LED drivers recycle
the current from the eight inputs to provide visual input
status indication without any additional current or power
consumption.
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 pincompatible
version of this device, the MAX31913, which
does not include the patent-pending current-switching
circuitry included in the MAX31912.
Applications
- Digital Input Modules for PLCs
- Industrial, Building, and Process Automation
- Motor Control
