![]() ![]() ![]() ![]() If the field power supply is not available, then U1 can be powered from the controller side. ![]() U1 (MAX31911) is powered by a 24V field power supply in most cases. On the Pmod side, the voltage supply can be 3.3V or 5V on the U1 side, the voltage supply is 5V. The Pmod specification allows for both 3.3V and 5V modules as well as various pin assignments. U3 (MAX14850) accomplishes 6-channel data isolation in a Pmod™-compatible form factor. Current-voltage comparison of a single input channel in both the traditional and Corona (MAX31911) design approaches. For additional flexibility, the integrated 5V voltage regulator can power external optocouplers, digital isolators, or other external 5V circuitry.įigure 4. A multibit CRC code, transmitted through the SPI port for each 8 bits of data, ensures reliable communication in noisy industrial environments. On-chip 8-to-1 serialization eliminates optocouplers needed for isolation. Selectable on-chip lowpass filters allow flexible debouncing and filtering of sensor outputs. Figure 4 compares the current-voltage relationship of a single input channel in both approaches. Input current limiting significantly reduces the power consumed from the field voltage supply when compared to traditional discrete resistor-divider implementations. It provides the front-end interface to a PLC digital-input module. In this design the industrial digital-input serializer (U1) translates, conditions, and serializes the 24V digital output of sensors and switches to CMOS-compatible signals required by microcontrollers. Here U1 is the MAX31911 octal translator/serializer and U3 is the MAX14850 6-channel data isolator. Diagram of the digital-input subsystem reference design. The Corona reference design board, (MAXREFDES12#).įigure 3. The Corona input module is seen in Figure 2 with the system diagram in Figure 3. Let’s take a closer look at the hardware and software. The design integrates an octal digital-input translator/serializer, a 6-channel data isolation device, and an H-bridge transformer driver for an isolated power supply if field power is not available. The design accepts high-voltage inputs (36V, max) and features isolated power and data, all integrated into a small 90mm x 20mm form factor. The Corona design provides the front-end interface circuit of a PLC digital input module. The solution to the above design objectives is the Corona isolated subsystem reference design utilizing a digital-input translator/serializer and a data isolator. Implementing an Isolated Digital-Input Reference Design Integrate all this functionality and you make the digital input far more versatile and robust, generate less heat and use less power, save space, and lower costs significantly. ) Improve error detection and make data transfer very reliable over that same simple interface. Use configurable current limiting to lower the power dissipation. Now turn to data serialization and find a way to eliminate the optocouplers used for isolation. First, increase the channel inputs to expand the system’s capacity, but keep the interface simple. Simple enough to say or plan, but not easy to do. Clearly the industry would benefit from a compact and simple, isolated digital-input interface. For high-channel-count modules, moreover, the multiple optocouplers increment system costs and power consumption, while consuming valuable board space. Hot spots can even reduce system reliability. In this traditional architecture the resistor-dividers consume high power and generate PC board (PCB) “hot spots” that can require the design to support a higher operating temperature and add a heatsink. ![]()
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