Implementing Functional Safety in Motor drives
All the safety functions should satisfy the requirements defined in part 5-2 of the IEC standard 61800 for variable speed drive systems. This video integrates four TI designs and demonstrates how the safe torque off (STO) and safe brake control (SBC) functions can be integrated in variable speed drives. The details of the TI Designs used in this demonstration are as follows:
The motor is powered up by TIDA-01420, which is a basic isolated power stage. This design uses UCC53XX as gate driver and has the option to populate the 3 variants of the gate driver on the same board. The gate driver needs a bipolar supply of +15V,0V,-8V.
The gate drivers are powered from another TI Design i.e. TIDA-00199. TIDA-00199 is an isolated power supply design which takes 24-V as the input and gives the desired voltage rails at the output.
TIDA-01599 implements the hardware turnoff of the motor. The emergency switch when pressed sends an STO signal to TIDA-01599. When the STO is triggered, the design disconnects the 24V input to the power supply design (TIDA-00199). TIDA-01599 uses ISO1212 as an isolated digital input receiver, TPS27S100 as the high side switch and TPS22860 as load switch. Although the power is disconnected from the motor, the shaft of the motor is free to rotate which again creates a safety hazard. So, there is an another safety related design for holding the shaft of the motor.
TIDA-01600 controls the braking of the motor. The brake of the motor has an electromagnetic switch. When a voltage of 24V is applied to the brake, the shaft is free to rotate. TIDA-01600 uses TPS27S100 and ULN2003A as switches to control the electromagnetic brake.