A5931 on left, and conventional equivalent on right
The chip, called A5931, includes output mosfets and a built-in control algorithm running on a state-machine – easing ASIL automotive qualification, claimed the firm, because there is no microcontroller whose software would have to be examined in detail.
Motor parameters are stored in on on-chip EEPROM.
Interactive (with on-screen sliders) Windows-based design software is available to establish appropriate motor parameters, or they can simply be typed in if already known.
Start-up, in some ways the trickiest part of sensor-less operation, is through an align-and-hold process – treating it as a stepper motor – to generate enough back emf to determine rotor position.
Also for development, a built-in test mode allows many – millions if necessary, a spokesman told Electronics Weekly at PCIM – automated re-starts from stationary to gather start reliability data. One PC can control multiple development boards for start testing.
Originally developed for 25,000rpm server fans, speed control is 5% over temperature and typically 1% – necessary because in servers, said the spokesman, fans are sometimes operated in tandem where efficiency drops if the fan speeds are not matched.
A second version of the chip – A5932 – drives external n-channel mosfets for larger motors and operates in both sine and trapezoidal wave – the latter to increase torque.