September 19, 2019
| By: Christine Young
Blogger, Maxim Integrated
Earlier this year, Andrew Smith, a product manager on Maxim’s industrial communications team, blogged that “These Industrial Communications ICs Are Oldies but Goodies for Good Reason.” His point was that innovation isn’t only about the latest and greatest products, but it is also exemplified by creating something that is lasting and continues to address emerging requirements for years. In his post, Smith highlighted several interface and signal routing ICs that continue to help engineers simplify their designs, reduce costs, and miniaturize their end products.
There are many more industrial communications solutions that fit this bill. In this post, I’ll note a few that you might want to consider for your next industrial design.
Industrial automation applications benefit from the robust communication that industrial communications ICs with isolation can support.
For industrial automation equipment, it’s become valuable to use a low-voltage microcontroller to measure high voltages (12V to 300V) and currents. You can, for instance, check for an unstable AC or DC power supply and, ultimately, protect the equipment against surges and overloads. To interface high-voltage circuitry to low-voltage circuitry, you do need to locate a block of isolation circuitry at the interface. This galvanic isolation between the high-voltage field-side and low-voltage logic-side circuits provides a way to avoid a direct conduction path between the two sides, which prevents current from accidentally reaching ground via the human operator of the equipment. Such isolation also prevents propagating noise and ground loops between the two sides. A traditional discrete isolation approach relies on transformers for power isolation and optocouplers (or digital isolators) for the data isolation barrier. However, this approach does require a lot of space and can be costly to implement.
The MAX14001/MAX14002 isolated analog-to-digital converter (ADC) provides the field-side and isolation circuitry in a single package. The device brings together a single-channel, 10-bit successive approximation register (SAR) ADC with CMOS capacitive digital isolation circuitry, enabling accurate transmission of a digital signal between two electrically isolated domains via a capacitive dielectric. This results in 3.75kVRMS of integrated isolation between the high-voltage field side and the low-voltage comparator output/SPI (logic) side. Since it has an integrated, isolated DC-DC converter to power all of the field-side circuitry, field-side diagnostics can be run even without any input signal. The device helps to simplify power routing and meet space-constraint requirements. The MAX14001PBM peripheral module provides the hardware needed to evaluate the MAX14001 to measure two channels of data, line voltage, and load current. A simple USB cable provides all of the power and communication.
The 4-20mA current loop is the dominant analog signal for transmitting process information in process control applications. Its reliability stems from the fact that current remains the same throughout the loop. It is also fairly simple to configure and connect. Its cost and complexity, however, are affected by voltage drops and the number of process variables that have to be monitored. More process variables require the implementation of more loops and this, in turn, calls for proper isolation of independent loops to prevent problems with ground loops. The current loop includes a sensor transmitter to convert measurements from its sensor into current signals (between 4mA and 20mA). There are 2-wire, 3-wire, and 4-wire sensor transmitter configurations, each with their own advantages and disadvantages.
The MAX12900 is an ultra-low-power, highly integrated analog front-end (AFE) that implements a 4-20mA sensor transmitter. The device converts pulse-width modulation (PWM) digital data from microcontrollers without a dedicated digital-to-analog converter (DAC) output into a current signal over a 4-20mA loop with 2-, 3-, or 4-wire configurations. It can be used in sensor transmitters that measure pressure, temperature, flow, and other parameters. Compared to traditional solutions, the MAX12900 saves up to 50% in power (operating at 250µA max), is very accurate, and helps simplify designs by integrating 10 building blocks into a 5mm x 5mm package. The MAXREFDES1161# reference design provides a platform for fast and easy prototyping with the MAX12900. The reference design includes test data that shows the accuracy and robustness of the IC. You can also learn more from the application note, “How to Implement a 4-20mA Transmitter with the MAX12900.”
Industrial applications such as building automation, switching gear, and industrial controls can all benefit from integrated protection for more robust communications. One way to improve communication as well as safety is by integrating galvanic isolation between the CAN-protocol controller side of a device and the physical wires of the CAN network cable-side/bus-side of the transceiver. Such isolation is beneficial because it breaks ground loops and reduces noise where there are large differences in ground potentials between ports.
The MAX14882 5kVRMS isolated high-speed CAN transceiver provides this galvanic isolation. Its integrated transformer driver and LDO enable simple isolated power designs. The IC’s polarity reversal feature simplifies installation of end products like motion controllers, fieldbus networks, and backplane buses. The device’s CANH and CANL I/Os are fault tolerant up to ±54V and are protected from electrostatic discharge (ESD) up to ±15kV to GNDB on the bus side (as specified by the Human Body Model).
In summary, some things just keep getting better over time. Wine, a good pair of jeans, and, for your industrial designs, these proven industrial communications ICs.