Tiny motor driver now in the world's top 10

The STSPIN820 motor driver, from STMicroelectronics, was recently awarded a 2018 Top 10 Power Product Award from 21ic.com and Electronic Products China (EPC), both top Chinese media. A prestigious honour that recompenses technological breakthroughs and game-changing innovations, the award recognises what is believed to be the smallest 45 V motor driver in the world that can achieve a resolution of up to 256 microsteps.

To better meet the needs of engineers who prefer smaller products, ST focused on a monolithic architecture — in other words, the control logic, the two independent pulse-width modulators (PWM) current controls and the power stage, made of two protected full-bridges, are all on the same die. As a result, the product can fit in a tiny 4 x 4 mm package and still have an operating voltage between 7 and 45 V. This upper limit tells design teams the device can work in systems requiring 10, 24 or even 36 V, since the motor driver will still have enough headroom to account for the usual variations that may occur at the power supply. Thus, a 45 V rating implies compatibility with a vast range of embedded systems.

To achieve a high resolution of 256 microsteps, ST had to develop a precise PWM current control algorithm, using the integrated comparator to evaluate in real time the current flowing to the motor against the current defined by the digital-to-analog converter (DAC) for the next step. Furthermore, since ST’s algorithms are able to keep the torque ripples under control, the motor driver can offer quieter operations than competing devices.

Optimising the architecture also means that ST did without the embedded microcontroller that’s present on its other STSPIN components, because the nature of the STSPIN820 demands a different approach. Engineers looking to build a mobile electronic device will have a host MCU that can easily handle this type of workload, which means they don’t need to offload it to the driver. Hence, by designing an architecture devoid of such engine, ST reduced the size of its die, with no negative repercussions on the end product. The judges were particularly impressed by the product’s 500 mΩ R_DS(ON) MOSFETs, despite its small package.

For more information on the award-winning product, visit https://blog.st.com/ststpin820-motor-driver/.