Robot Motor Control using Automotive Electronics

L9949

Automotive electronics can be a great source of inspiration for robot motor controls.   I’ve covered some aspects of H bridge construction including low side switches, high side switches, and current sensing.   Sometimes its preferable to build your own H-bridge circuit, while other times it might be desirable to use an H bridge integrated chip.

It is worthwhile to cover some of the benefits of using discrete components to build your own H bridge circuit.

  • You have better control over the specifications in each component of your motor driver.
  • Second source parts can be located making manufacturing less likely to be impacted by parts shortages/cancellations.
  • Power dissipation issues can be addressed with custom placement of components.

Other times your design can benefit from using an integrated chip.  Here are some of those benefits.

  • Integrated chips are smaller
  • They often incorporate special functions like over-temp and over-current shutdown.
  • Manufacturing costs can be reduced since only one component is placed on the PCB.

My preference is to use integrated chip solutions for any motor drive system using less than 3A continuous.  There’s also something you can look for that can improve performance and durability in a motor controller IC.  Look at parts designed for the automotive electronics market.

Why look at these parts?  The auto industry is a large and demanding market.  They release a high cost product to consumers and mandate robust automotive electronic components that don’t fail.  The cost to recall a product due to a poor part performance is immense.  As an engineer / inventor you can benefit from all of the research and performance enhancement that goes into designing parts for the automotive industry.

Lets look at the ST Microelectronics L9949 door controller IC as an example (L9949 datasheet, L9949 web page).   The part is designed to control an automotive mirror.  There are a few things this part won’t do.  It’s not terribly useful for robots drive systems (wheel control) since its H bridge control is basically on/off versus proportional.  But the part does have an integrated reversible H bridge, two half-bridges, and a high-side driver.  These components are all protected with over-temperature, over-current, under-voltage, over-voltage, short-circuit, and open-circuit detection and/or protection.  The part datasheet even states that external freewheeling protection diodes are not needed for inductive loads on OUT1-OUT5.  The exception is OUT6, the high-side driver, which is designed to drive resistive loads.

The L9949 is rated for 6A, but IC current ratings are dependent on circuit layout and cooling efforts. Sitting on a PCB with no fan/heat sink this part could probably handle 2A continuous.  Since the part is designed for an automobile voltage (13.5VDC) it runs between 7 and 22V, which is perfect for a 12V robot.  It has an SPI interface for controlling motors, or other loads, connected to the bridge circuits and a current monitor analog feedback.

The manufacturer states that the H bridge may be used to control door latch or mirror retracts, the half-bridges can control mirror axis motors, and the high-side switch can be used to control a mirror defrost element.  When I see a part like this all sorts of potential applications come to mind.  Telescoping tools, cutters, heating elements, blowers, pumps, lights and all sorts of other loads could be controlled with this part.

Anyway, when your looking for parts for your design, be sure to check out automotive applications on the web site of any IC manufacturers you visit.

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