Teensy3 power mods

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bmsi

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Once saw a discussion on changes on the Teensy3 pcb to allow standalone operation but
maintain the ability to use the USB. Anyone know where that discussion is ?

Thanks in agvance,
Bill
 
I don't know a link to that discussion, but I can tell you Teensy3 is designed to make this easy. Just cut the pads apart on the bottom side of the board. Then VUSB and VIN are disconnected. You can safely apply 5V power to VIN without it feeding back to VUSB.
 
PaulStoffregen said:
I don't know a link to that discussion, but I can tell you Teensy3 is designed to make this easy. Just cut the pads apart on the bottom side of the board. Then VUSB and VIN are disconnected. You can safely apply 5V power to VIN without it feeding back to VUSB.
Click to expand...

I thought there was something in addition (a cap?) to keep the USB usable?

Thanks for the reply,
 
bmsi said:
I thought there was something in addition (a cap?) to keep the USB usable?
Click to expand...

That's only needed for USB host mode, which isn't supported by any software yet. But when host mode software is written, if your power supply isn't strong enough to hold up the 5V power when a USB device is hot-plugged, you can solder a 150 uF capacitor to the bottom of the board. Odds are whatever 5V power supply you use will work fine. But if hot-plugging a USB device crashes or reboots your Teensy3, that place to add a capacitor will be there.
 
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PaulStoffregen said:
That's only needed for USB host mode, which isn't supported by any software yet. But when host mode software is written, if your power supply isn't strong enough to hold up the 5V power when a USB device is hot-plugged, you can solder a 150 uF capacitor to the bottom of the board. Odds are whatever 5V power supply you use will work fine. But if hot-plugging a USB device crashes or reboots your Teensy3, that place to add a capacitor will be there.
Click to expand...

way cool.

Thanks again.
 
I was wondering if it's possible to use an external 3.3V regulator to provide the MK20 chip with juice, bypassing the built in regulator which is limited to around 120mA. According to the datasheet containing the electrical specs, it shouldn't be a problem connecting 3.3V to VDD (best to cut the VUSB trace on the Teensy board tho)?
 
Yes, applying 3.3V works. But do be careful, because with direct connection there's no protection against reverse polarity. If you connect the power backwards, it will destroy the board.
 
Luckily my power supply circuits always contain a inline diode and most of the times a crowbar circuit, ensuring neither the power supply nor the input pins try anything funny :) .
 
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