Analog Front End (AFE) for Merging Units and Multi-Function Protection Relays Reference Design
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Key Document


This solution addresses the front end needs of Merging Units where multiple measurement channels for current and voltage are required. This implementation is modular, allowing easy expansion of channels while at the same time keeping the connectivity to the processor minimal by using the SPI daisy chain feature in the TI's SAR ADC. Additionally, this solution is compact because the AFE not only integrates the front end circuitry for each channel, but also integrates a voltage reference with low temperature drift

  • Integrated AFE solution including PGA and reference
  • The solution enables high accuracy without calibration and lower temperature co-efficient (reduces variation in accuracy due to change in temperature)
  • Modular approach + minimal MCU connectivity overhead
  • Increase number of input channels by adding additional SAR ADCs
  • Using daisy chain concept, the same SPI interface is used to connect multiple SAR ADCs
  • Measurement capabilities for protection and metering leveraging the higher sampling rate on the ADC

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Schematic/Block Diagram

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Design Files

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TI Devices (2)

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Part Number Name Product Family Sample & Buy Design Kits & Evaluation Modules
ADS8688  16-Bit 500kSPS 8-Channel Single-Supply SAR ADC With Bipolar Input Ranges  Analog-to-digital converters (ADCs)  Sample & Buy View Design Kits & Evaluation Modules
TPS709  150-mA, 30-V, ultra-low-IQ, low-dropout voltage regulator with reverse current protection & enable  Power management  Sample & Buy View Design Kits & Evaluation Modules

CAD/CAE symbols

Part # Package | Pins CAD File (.bxl) STEP Model (.stp)
ADS8688 Download
TPS709 Download

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Technical documentation

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User guides (1)
Title Type Size (KB) Date
PDF 1768 13 Oct 2016
Design files (6)
Title Type Size (KB) Date
ZIP 339 10 Oct 2014
ZIP 2103 10 Oct 2014
PDF 208 10 Oct 2014
PDF 658 10 Oct 2014
PDF 105 10 Oct 2014
PDF 1195 10 Oct 2014

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