Reference design revisits industrial PLC interfacing
Designers now have a way to reduce power, system cost, and size for programmable logic controller (PLC) digital-input subsystems, with the Corona (MAXREFDES12#) reference design. This design reduces isolated channels and exploits analogue integration for industrial control and automation applications.
One method of reducing the size of I/O solutions in PLCs is to reduce the number of digital channels that need to be isolated. Integrating three Maxim products including a transformer driver, the Corona design reduces isolated channels and eliminates the need for power-hungry optocouplers and discrete parts. These savings can reduce power by 16%, solution size by 38%, and cost by 23%. Maxim’s devices used in Corona are designed specifically for harsh industrial environments with operating temperature ranges from -40°C to +125°C, so they are ideal for use in PLCs and other automation applications. Advantages include;
– Analogue integration, reducing isolation channels to four while Maxim’s digital isolator eliminates the need for optoisolators; optimised for 16, 24, and 32 input channel designs, the digital input serialiser’s SPI buses can be daisy-chained to further reduce isolation channel count, leading to increased savings
– Lower power: uses 16% less power than the traditional design approach
– Lower cost: uses 38 fewer parts than a traditional design to create a less expensive integrated solution
– Smaller size: provides 51% fewer components than a traditional design.
The specific products used in the Corona design are;
– MAX31911: an industrial, octal, digital input translator/serialiser that delivers lowest power consumption and reduces component count on the board
– MAX14850: a 6-channel digital isolator that enables low power consumption and stable high-temperature performance; UL1577, CSA, IEC 60747-5-2 safety certified. Replaces optoisolators, which have limited LED lifespan, with a 5x longer life solution
– MAX13256: a 36V H-bridge transformer driver that simplifies isolated power designs
The complete reference design is available in a 90 x 20mm Pmod form factor, at $45.
Maxim Integrated; www.maximintegrated.com
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