Though the pervasiveness of brushless DC (BLDC) motors is increasing all the time within a wide variety of different sectors, in an automobile context the value of brushed motors still remains clear. These devices present vehicle manufacturers with highly effective solutions delivering strong performance levels, while simultaneously occupying very attractive price points.
Brushed motors are more appropriate than BLDCs in situations where they are in use for only a relatively small proportion of the time. As well as door mirror positioning/folding systems, camera lid control mechanisms, grill shutters, electronic throttle control (ETC) and exhaust gas recirculation (EGR) systems, there are new applications where they are now starting to be employed. These include things like automated charging socket openers in electric vehicles (EVs), for example.
The bi-directional motor control necessary in the applications previously outlined is undertaken via a H-bridge circuit. The MCU is able to interface with the relevant electronic control units (ECUs) within the car through the in-vehicle networking infrastructure. It is provided with key diagnostic data from the pre-driver. The H-bridge drivers are responsible for delivering power to the motor.
To minimise board utilisation, keep the component count down and reduce the number of potential points of failure, there are pressures to integrate these parts together. Embedding the pre-driver into the MCU seems to make sense at first, but it goes against automotive engineers’ preferred tactic of design reuse. It means that a lot of additional coding and development work will be needed for each new implementation. By combining the pre-driver with the H-bridge instead, there will be far less coding to worry about.
Integrating two H-bridges and the pre-driver elements into a single device, even greater benefits can be derived - further reducing component count and saving more board real estate. This is the approach that Toshiba has taken with its AEC-Q100 compliant TB9053FTG and TB9054FTG driver ICs. Each of them consists of two N-channel DMOS H-bridge drivers. These can control two separate 5A motors or a single 10A motor when operated in parallel.
A white paper on this more integrated approach to electric motor control has been published by Toshiba and can be downloaded below: