Reference design revisits industrial PLC interfacing

August 28, 2013 // By Graham Prophet
Maxim Integrated's "Corona" reference design introduces an alternative architecture for industrial PLC digital-input modules that reduces the isolated channel count, simplifying input structures while reducing power, system cost, and size

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