TÜV SÜD-assessed safe torque off (STO) reference design for industrial drives (IEC 61800-5-2)


Design files


This reference design outlines a safe torque off (STO) subsystem for a three-phase inverter with CMOS input isolated IGBT gate drivers. The STO subsystem employs a dual-channel architecture (1oo2) with a hardware fault tolerance of 1 (HFT=1). It is implemented following a de-energize trip concept. When the dual STO inputs (STO_1 and STO_2) go active low, the corresponding power supplies of the primary and secondary side of the six isolated IGBT gate drivers, are cut off through load switches. This removes the possibility to control and energize the motor. The STO reference design (1oo2) has been assessed by TÜV SÜD to be generally suitable for SIL 3 and PL e/Cat. 3.

  • Dual-channel STO architecture (1oo2) assessed by TÜV SÜD to be suitable for SIL 3 (IEC 61508) and PL e/Cat. 3 (ISO 13849)
  • TÜV report, safety concept description and qualitative system FMEA available to further help designers implement the STO subsystem
  • STO subsystem for three-phase inverters with CMOS-input isolated IGBT gate drivers such as ISO5852S, UCC21750 or UCC5350
  • 24-V isolated input receivers ISO1211 compliant to IEC 61131-2 and ±60-V input tolerance with reverse polarity protection
  • Interface to MCU (SIL 1) for diagnostic coverage of the load switches in the STO subsystems
  • Option to monitor input and output supply UVLO of the ISO5852S through RDY pin and additional monitoring capabilities with UCC21750 integrated analog-to-PWM isolated sensor
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Design files & products

Design files

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Reference design overview and verified performance test data


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Complete listing of design components, reference designators, and manufacturers/part numbers


Detailed overview of design layout for component placement


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Design file that contains information on physical board layer of design PCB


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Includes TI products in the design and potential alternatives.

Digital isolators

ISO7710Robust EMC, single-channel, reinforced digital isolator

Data sheet: PDF | HTML
High-side switches

TPS27S10040-V, 80-mΩ, 4-A, 1-ch, Industrial high-side switch with adjustable current limit

Data sheet: PDF | HTML
IO-Link & digital I/Os

TIOS1013Digital sensor output driver with integrated surge protection and 3.3-V LDO output

Data sheet: PDF | HTML
Isolated digital inputs

ISO1211Single-channel Isolated 24-V to 60-V digital input receiver for digital input modules

Data sheet: PDF | HTML
Isolated gate drivers

ISO54525.7kVrms, 2.5A/5A single-channel isolated gate driver w/ split output, STO & protection features

Data sheet: PDF | HTML
Isolated gate drivers

ISO5852S5.7kVrms, 2.5A/5A single-channel isolated gate driver w/ split output, STO & protection features

Data sheet: PDF | HTML
Isolated gate drivers

UCC217505.7kVrms ±10A, single-channel isolated gate driver w/ DESAT & internal miller clamp for IGBT/SiCFETs

Data sheet: PDF | HTML
Isolated gate drivers

UCC53503kVrms, 5A/5A single-channel isolated gate driver with miller clamp or split out & 8V or 12V UVLO

Data sheet: PDF | HTML
Load switches

TPS229195.5-V, 1.5-A, 90-mΩ load switch with adj. output discharge

Data sheet: PDF | HTML

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Design tools & simulation

Simulation model

TIDA-01599 Simulation Files — TIDM042.ZIP (534 K)

Technical documentation

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Type Title Date
* Design guide TUEV-Assessed STO Reference Design for Industrial Drives (IEC 61800-5-2) (Rev. B) PDF | HTML Nov. 11, 2022
Functional safety information FMEA STO Concept TIDA-01599 May 17, 2022
Functional safety information Overview STO Concept TIDA-01599 PDF | HTML Apr. 19, 2022
Functional safety information STO Concept TUEV Report TF97657T Rev.1.1 Feb. 24, 2022
Functional safety information Design Smaller Safe Torque Off (STO) Systems Using 3-Phase Smart Gate Drivers PDF | HTML Mar. 04, 2021
E-book Ein Techniker-Leitfaden für Industrieroboter-Designs Mar. 25, 2020
E-book E-book: An engineer’s guide to industrial robot designs Feb. 12, 2020

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