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Unread 13-05-2009, 14:07
AustinSchuh AustinSchuh is offline
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FRC #0971 (Spartan Robotics) #254 (The Cheesy Poofs)
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Re: Review of a small motor controller schematic.

Quote:
Originally Posted by EricVanWyk View Post
I got in a small fight with the 33887 with regards to 5V tolerant. Don't worry, you are fine. The 33887 can handle 3.3V inputs just fine, but it has very small pullups to 5V. The chip I was driving it with couldn't handle its inputs being pulled above 4Vish, so I had to buffer it.
Using this suggestion, I think I've updated the schematic to use the 33887 correctly. If wiring the 3.3 volt I/O lines from the controller doesn't work, I'll grab a knife and cut the trace and add a buffer/transistor. I'll update the layout once the rest of the schematic stops changing.

Al,
Thanks for pointing me to the page for the regulator again. It says that a 10µF tantalum capacitor is recommended and that Aluminum electrolytic types of 50µF or greater can also be used. I also took the time to read about the heat dissipation recommendations in the spec sheet this time around, and I'll be updating my layout accordingly to add some more copper to dissipate heat when I do the layout for the 33887.
Attached Files
File Type: pdf MotorBoard2.pdf (76.0 KB, 41 views)