Lock Step Microcontroller Delivers Safe Motor Control
Texas Instrument's (TI) Hercules line of safety processors (see Lockstep Microcontroller For Industrial Applications) expanded with their new TMS570 Arm-based multicore processors designed for applications like motor control. The dual core, Cortex-R4 processors operate in lock step with hardware-based fail safe detection support.
Designing safety oriented processors like the Hercules line is technically challenging. The applications where these chips can be used are also challenging for designers. TI's hardware and software combination make this job significantly easier.
Multicore lock step micros are often employed in automotive applications like Freescale's triple core Qorivva (see Three Core Micro Pushes Powertrain Performance). It has two Power architecture cores that run in lock step mode while a third handles communication chores.
What makes the new announcement from TI more interesting is the addition of the TPS65381-Q1 power supply chip and the DRV3201 gate driver designed to work with the new TMS570 parts (Fig. 1). The two support chips have serial interfaces allowing the processor to monitor their operation.
Figure 1. The 180MHz TMS570 SoC has a pair of Arm Cortex-M4 cores running in lock step. They are designed to work with the TPS65381-Q1 power supply and DRV3201 gate driver chips to provide motor control in safety oriented applications.
The design of the processor and its support chips addressed safety and reliability as well as the ability to monitor all aspects of the system. The 180 MHz process has up to 3 Mbytes of flash plus RAM storage and all that storage has ECC (error correcting code) support. There is also extensive on-chip clock and voltage monitoring. The ability to monitor the support chips is also provided via a serial SPI interface. All the chips include built-in self test (BIST) support in addition the status monitoring support.
The TMS570 has the usual complement of memory, serial and parallel interfaces including versions that support CAN and Flexray. There are two ADCs (analog-digital converter) as well.
The TPS65381-Q1 power management chip provides power to the chip. It has its own watchdog timer and it can reset microcontroller if error signal received from the microcontroller. This would be driven by the comparison hardware for the two lock step micros.
The DRV3201-Q1 motor driver chip is designed for safety-critical applications. It support three phase, brushless DC (BLDC) motors via six N-channel MOSTFET transistors. The chip can handle gate charges of 250 nC. The drivers are programmable allowing for easy slope adjustment. A boost converter is integrated with the FETs and it provides overdrive voltage for better control a the power-stages even. It run on voltages down to 4.75 V.
The motor control interface includes quadrature encoders like those fuond on Texas Instruments' C2000 family (see DSC Lets Coprocessor Handle Real-Time Analog). The Hercules also uses sensor feedback to implement a "virtual encoder" (Fig. 2). This allows the software to compare the operation of the motor using two encoders, one logical and one physical, without the need for a second set of encoder sensors.
Figure 2.TI supports "virtual encoder" software that allows the system to complement encoder hardware and compare results to track motor operation.
The new chips are part of TI's SafeTI program. There is also a qualification kit for compilers used with the system to streamline third party certification often required for deploying solutions in safety critical environments. There are different design packages for industrial, automotive and quality managed applications.
TI is also providing a range of development kits. The motor control kit includes TI's MotorWare and InstaSPIN motor control software. This includes the support for the virtual encoders.
