96-Channel Bidirectional Digital Input Module Reference Design for PLC
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Key Document


This reference design is a compact implementation of 96 isolated digital input channels using the ISO1212, an isolated digital input receiver. This design shows the current limit feature of the ISO1212 device which has better thermal performance than traditional optocoupler solutions. This design makes a digital input board with multiple channels more compact and decreases board temperature (less than 50°C). A MUX and decoder with the ISO1212 device decreases the number of pins of the microcontroller from 96 to 8. The design was tested with 100-kHz input signals (200- kbit) per channel. The design uses less than 7.3 W of input power which results in less heat dissipation. All signals are designed to withstand ESD, EFT, and surge events according to IEC6100-4.

  • 96-channel bidirectional digital input module
  • Voltage Inputs: 24-VDC Range, Limited to 3.1 mA Per Channel
  • Compact and Low Temperature Rise (< 50°C at 1hour) Design with all 96 channels on
  • Serial Output Option
  • Tested to 0.5 kV, 42 Ω IEC 61000-4-5 surge test for industrial signal lines

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Design Files

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TI Devices (3)

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Part Number Name Product Family Sample & Buy Design Kits & Evaluation Modules
CD74HC238  High Speed CMOS Logic 3-to-8 Line Decoder Demultiplexer Inverting and Non-Inverting  Specialty logic ICs  Sample & Buy View Design Kits & Evaluation Modules
CD74HC4067  5-V, 16:1, 1-channel analog multiplexer  Switches & multiplexers  Sample & Buy Not Available
ISO1212  Dual-channel Isolated 24-V to 60-V digital input receiver for digital input modules  Isolated interface ICs  Sample & Buy View Design Kits & Evaluation Modules

CAD/CAE symbols

Part # Package | Pins CAD File (.bxl) STEP Model (.stp)
CD74HC238 Download -
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CD74HC4067 Download Download
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ISO1212 Download Download

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Technical documentation

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User guide (1)
Title Type Size (KB) Date
PDF 4699 11 Jul 2018
Design files (6)
Title Type Size (KB) Date
ZIP 1005 11 Jul 2018
ZIP 2899 11 Jul 2018
PDF 6334 11 Jul 2018
PDF 237 11 Jul 2018
PDF 97 11 Jul 2018
PDF 1845 11 Jul 2018

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