Custom Teensy PCB assembly replacement parts

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yeahtuna

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Hi all,

I've been on a long and interesting adventure as I go through all the steps towards getting my first batch of teensy 3.2 based devices produced and assembled in a factory.

I'm currently making arrangements with a fab / assembler. I've been asked to approve replacement parts and I was hoping someone here might be able to give me some advice. I'm not an electrical engineer, and I don't even know where to start to figure out if the replacements are okay. Here are the parts:

  • They want to use 400ma ferrites.
  • For the two 33R resistors on the D+ D- USB signals, they want to use 1/10W resistors.
  • For the crystal, they want to use part 8Z16000001 (16MHz 10pF -20C +70C). Based on the Crystal Guildlines, this seems like it should be okay.
  • Lastly my device has some resistors for MIDI DIN ports. For the two 47R resistors on MIDI Out, and the 220R and 270R resistors for MIDI In, the fab wants to use 1/10W resistors.
Thank-you in advance for any schooling you can offer me.

Regards,
Rob
 
I take it this is basically using larger parts to make assembly easier/use stock they already have?

Ferrites will constrain the current through them, so a check on current draw of your prototype will give you and answer there.

On USB the lower spec resistors will work, but your design in theory is supposed to be able to handle having the pins shorted to each other and or 5V/gnd. In those cases I think a 1/10W resistor will be operating outside it's spec with ohms law saying .75W but wasn't able to confirm what the chip does in those cases since the Teensy doesn't have 1W transistors there either and the chip wouldn't be able to sustain that either so assuming it has internal protection.

With the Midi resistors it's standard IO current limits, so 47ohms on midi out could have 3.3V/47R = 70mA (beyond the 20mA pin spec) * 3.3V =0.23 W. Which is outside the 0.100 resistors but is also assuming a short circuit condition. Driving into the design impedance at the far end the current/power will be far less. Here I'd say the pin driver would fail before the resistor did.
 
Thank-you for replying. Yes, the Teensy components are all 0603, except for the 2.2 uf caps which are 0805. The reference design I started with used those footprints and I just stuck with them. It would seem to me that the larger components should be able to handle more power, so I'm guessing those replacements should all be fine. My prototype draws about 35ma, so those ferrites should be fine as well. Thanks again for your feedback.

Rob
 
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