24-VAC multi-channel solid state relay reference design using digital isolator
TIDA-010085
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Key Document

Description

This reference design demonstrates a multi-channel solid state relay (SSR) using a single isolation. The design uses a multi-channel digital isolator with a single isolated power supply and common ground gate-drive circuit to control multiple SSRs independently. The design is rated for 24-VAC powered relays with current rating up to 2 A, but scalable up to 240 VAC and higher current rating. Each SSR channel consumes less than 75-mm2 space with a maximum height of the component around 3-mm, enabling considerable size saving compared to electromechanical relays. The use of single isolated power supply reduces board space and BOM cost.

Features
  • Multiple solid-state relays using a single isolation with multichannel digital isolator, easily scalable to any number of SSR channels with minimum extra cost
  • SSR drive voltage 24 VAC ±20%, drive current 2-A RMS (voltage and current rating, scalable by using appropriately rated components)
  • SSR turn on and turn off time: 15–300 μs (adjustable), average current consumption per SSR drive (referred to primary) < 4 mA (adjustable down to 20 μA per channel)
  • SSR size < 75 mm2 per channel. Height is around 3 mm.
  • Functionally isolated open-loop flyback based power supply without the need of an MCU
  • Surge and switching overvoltage protection

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Schematic/Block Diagram

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Design Guide

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Design Files

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TI Devices (8)

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Part Number Name Product Family Sample & Buy Design Kits & Evaluation Modules
CSD17382F4  30-V, N channel NexFET™ power MOSFET, single LGA 1 mm x 0.6mm, 67 mOhm, gate ESD protection  MOSFETs  Sample & Buy Not Available
CSD19538Q2  100-V, N channel NexFET™ power MOSFET, single SON 2 mm x 2 mm, 59 mOhm  MOSFETs  Sample & Buy Not Available
ISO7740  Robust EMC, quad-channel, 4/0, reinforced digital isolator  Isolation  Sample & Buy View Design Kits & Evaluation Modules
ISO7760  Robust EMC, six-channel, 6/0, reinforced digital isolator  Isolation  Sample & Buy View Design Kits & Evaluation Modules
SN74LV1T34  Single Power Supply BUFFER Logic Level Shifter (no enable)  Voltage level translators  Sample & Buy View Design Kits & Evaluation Modules
TLC555  2.1-MHz, 250-µA, Low-Power Timer  Clocks & timing  Sample & Buy Not Available
TLV760  100-mA, 30-V, low-dropout voltage regulator  Power management  Sample & Buy View Design Kits & Evaluation Modules
TPL7407LA  30-V, 7-ch NMOS array low-side driver  Power switches  Sample & Buy View Design Kits & Evaluation Modules

CAD/CAE symbols

Part # Package | Pins CAD File (.bxl) STEP Model (.stp)
CSD19538Q2 WSON (DQK)| 6 Download Download
ISO7740 Download Download
Download Download
ISO7760 Download Download
Download Download
SN74LV1T34 Download Download
Download Download
TLC555 Download Download
Download Download
Download -
Download Download
TLV760 Download Download
TPL7407LA Download
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Technical documentation

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User guide (1)
Title Type Size (KB) Date
PDF 2639 22 Mar 2021
Design files (6)
Title Type Size (KB) Date
ZIP 527 19 Mar 2021
ZIP 1896 19 Mar 2021
PDF 383 19 Mar 2021
PDF 224 19 Mar 2021
PDF 359 19 Mar 2021
PDF 580 19 Mar 2021

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