Redundant dual-channel safe torque off (STO) reference design for AC inverters and servo drives
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Key Document


This reference design implements safe torque off functionality in variable speed drives (per IEC61800-5-2) by using dual channel isolated STO signals to control the inverter that supplies power to the motor. This is accomplished by independently enabling/disabling power to the isolated gate driver IC through load switches on VCC1 and VCC2. This reference design also provides diagnostic coverage for detecting various faults which helps in increasing safe failure fraction. 

This design uses ISO1212 as an isolated 24-V digital input receiver, compliant to IEC 61131-2 Type 1 characteristics to accept the two STO signals. Unlike traditional optocoupler solutions with discrete components having imprecise current limiting circuitry, the ISO1212 devices provide a simple, low-power solution with accurate current limits and a longer lifespan. The adjustable current-limit function of the load switch improves the reliability of the system. The ready pin of the gate driver, ISO5852S, helps in monitoring the supply rails.

  • Implements safe torque off (STO) to accomplish the Stop Category 0 specified in IEC 61800-5-2
  • Dual channel STO signals with multiple options for preventing generation of torque in the motor:
    • Disconnect power from the gate driver IC (both on low voltage and high voltage domains)
    • Generation of hardware trip signals to the terminate the PWM generation inside the MCU
  • Self-diagnostics coverage which includes monitoring safety pulses and detecting various faults within the circuit
  • ±60-V input tolerance with reverse polarity protection helps ensure STO pins are protected in case of faults
  • Accurate output current monitoring by the high side smart switch
  • Detection of input and output under-voltage lockout (UVLO) of the gate driver with ready (RDY) pin indication

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Design Files

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TI Devices (7)

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Part Number Name Product Family Sample & Buy Design Kits & Evaluation Modules
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
ISO5852S  2.5-A / 5-A, 5.7-kV RMS single channel isolated gate driver with split output and protection  Gate drivers  Sample & Buy View Design Kits & Evaluation Modules
LMZ14201  SIMPLE SWITCHER® 6V to 42V, 1A Power Module in Leaded Surface Mount TO Package  Step-down (buck) regulators  Sample & Buy View Design Kits & Evaluation Modules
SN74HC7001  4-ch, 4-input, 2-V to 6-V AND gates with Schmitt-Trigger inputs  Gate  Sample & Buy View Design Kits & Evaluation Modules
TPS22860  0.73-Ω, 5-V, ultra-low leakage load switch  Power switches  Sample & Buy View Design Kits & Evaluation Modules
TPS27S100  40-V, 80-mΩ, 4-A, 1-ch, Industrial high-side switch with adjst. current limiting and curren  Power switches  Sample & Buy View Design Kits & Evaluation Modules
TVS3300  33V flat-Clamp surge protection device  Circuit protection ICs  Sample & Buy View Design Kits & Evaluation Modules

CAD/CAE symbols

Part # Package | Pins CAD File (.bxl) STEP Model (.stp)
ISO1212 Download Download
ISO5852S Download Download
LMZ14201 Download Download
SN74HC7001 Download Download
Download Download
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TPS22860 Download Download
TPS27S100 Download Download
TVS3300 Download

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Technical documentation

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User guide (1)
Title Type Size (KB) Date
PDF 6569 25 Nov 2017
Design files (6)
Title Type Size (KB) Date
ZIP 208 28 Dec 2017
ZIP 2483 28 Dec 2017
PDF 968 28 Dec 2017
PDF 207 28 Dec 2017
PDF 67 28 Dec 2017
PDF 265 28 Dec 2017
E-book (2)
Title Type Size (KB) Date
PDF 12421 25 Mar 2020
PDF 3766 12 Feb 2020
Related Tools & Software

Reference Designs (1)

Hardware development (1)

Name Part Number Tool Type
C2000 Piccolo MCU F28027 LaunchPad™ development kit  LAUNCHXL-F28027  Development kit 

Models (1)

Title Category Type Size (KB) Date Views
TIDA-01599 Simulation Files PSpice Model ZIP 534 KB 28 Aug 2018

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