Reference design implements safe torque off functionality

23rd October 2018

Alex Lynn

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This reference design from Texas Instruments 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.

Features

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.

To learn more, click here.