Screaming Circuits: Meet Mark Rules, designer


Meet Mark Rules, designer

Mark works for a small company that designs and markets microcontroller development boards and motor drivers. The products tend to be used in small robotics projects, mostly in the education and hobby markets. They are starting to see more and more commercial business though, which is driving changes in product requirements.

Mark's new project requires that he take a current design controller board and make it as small as is possible with as few circuit changes as possible. The current board is 2” x 2.5” and uses a PIC 8-bit processor. It’s a pretty simple design that can control a pair of motor drivers and accept a variety of I/O connections.

The new version will combine the dual motor drivers on the controller board and still have almost the same I/O capabilities. The PIC18F2321, in a 6x6mm QFN package, looks to be the smallest Microchip processor that supports dual hardware PWM. He considered a 4x4mm QFN PIC16F690 using software PWM, but didn't like the performance hit.

For 5V regulation, he found the Microchip MCP1726 in a 3x3mm DFN package. The RS232 driver comes from ST micro, ST3243, in a 2.4x4mm FlipChip BGA. The dual motor driver is a pretty impressive 3x3mm A3901 from Allegro. That’s 64 square millimeters of chip space using QFN and BGA packages instead of 266 square millimeters for the processor alone in the old design.

The passive components come out to 4x 0201 parts, 4x 0402, 3x 0603, 3x 0805 and 2x 3216-18 capacitors. All of those should fit on the back of the board with enough room left over for a small TVS that may or may not be needed to suppress EMI from the motors. A few LED status indicators should also fit nicely on the top of the board.

Next comes the real challenge – super small connectors. Stay tuned.


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Super small connectors...ugh. Nothing I loathe more than working in increasingly tiny spaces...

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