Electronics Weekly Electronics Design & Components Tech News
Designed in accordance with ISO 26262 (2nd edition) and AEC-Q100-qualified, TB9083FTG is aimed at electric power steering, electric braking and shift-by-wire transmissions.
“A built-in fail-safe safety relay pre-driver complements the three-phase pre-driver,” according to the company, and the “SPI communication interface features an integrated CRC check.”
This IC is functional safety re-spin of the company’s earlier TB9081FG.
“Key improvements are robust functionality through redundancy and built-in self-test circuits – these are indispensable for compliance with ISO 26262,” said Toshiba. “In terms of redundancy, two band gap reference voltage circuits are built in [as in TB9081FG] as are two clock oscillation circuits. Built-in self-test circuits check whether internal diagnostic functions operate properly. These check results can be read out via SPI communication.”
Compared with the earlier part, the number of safety relay channels included to cut-off faulty loads have been reduced from five to three, due to customer demand, the company said, adding: “In the case of electric power steering, two channels could be applied to the power supply relay and the reverse polarity protection relay, and the other channel could be applied to the motor relay to cut the control circuit from the motor.
The silicon now fits in a 7 x 7mm 48pad VQFN (the older chip is 12 x 12mm), allowing one device and a spare to fit in the same area for redundant drive of the same motor. “Selection for the small package is deeply related to ISO 26262,” said Toshiba, which has put the wettable flank QFN through 3,000 cycles of thermal stress (-40 to 125°C, 20min soak, 10min ramp, so 1hr/cycle).
Another space-saver is that current sense amplifier gain and the reference voltage resistors are now on-die, with gain set via the SPI interface.
Something else that has been built-in, is a sequencer and verification circuit that monitors the mid-points of the three phases to detect external mosfet open and short-circuits (diagram left).
On-board error monitoring includes over-temperature and multiple under-voltage and over-voltage detectors.
