Teensy 3.0 Schematic Available

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Paul

Paul

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The Teensy 3.0 schematic is (finally) available now. :)

http://www.pjrc.com/teensy/schematic.html

schematic3.gif

Edit: this old schematic (posted November 2012) has a small error near the VUSB pin. Please use the schematic from the main website.
 
Thanks, Paul. What is the 1A dual diode-looking component? From the schematic I would assume that's a voltage regulator? Whatever it is, I think I've blown it somehow while running on external power...
 
It is a dual diode. I'd assumed it was a voltage regulator, but the schematic shows it's a dual diode used in parallel, and the 3.3V regulator is actually contained within the main ARM cpu (+5V goes through diode into VREGIN pin).

That is marked as a 1 A part and the Teensy does not use nearly that much current, so I'd be curious how it could be blown- unless by very high reverse voltage above the breakdown limit, but that would very likely kill the CPU also.
 
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Thanks, and yes I'm not sure what I could have done either. It seemed to suddenly die when I was working on the software side of things and now I'm not able to detect it over USB, though it is powered externally.
 
Yes, it's a 500 mA PTC "fuse", which it sometimes called a "poly fuse". It's the tall white part near the USB connector.

The 1A diode is a dual schottky diode. Even though the expected current is much less than 1 amp, I wanted to keep the voltage drop across the diode small for people who want to run from a 3.7 volt battery.

Regarding a dead board, have you tried the trick of holding the pushbutton before plugging in the cable?
 
PaulStoffregen said:
Regarding a dead board, have you tried the trick of holding the pushbutton before plugging in the cable?
Click to expand...

I actually didn't know about this trick, but I just tried it and it didn't seem to do anything. I confirmed that the fuse and the dual schottky diode are still working with a multimeter, so I guess the issue lies elsewhere.
 
Paul, you mentioned in an earlier post that there was reverse polarity protection when powering via Vin, which I see from the dual parallel diodes. But will reverse polarity applied to 3.3v harm the Teensy 3.0? Or is that also internally protected with circuitry inside the chip?
 
One follow up question, then, regarding reverse polarity: what is the function of the parallel diodes between VBAT and the chip's VBAT and VIN -> VREGIN? Do they provide any sort of protection from reverse polarity on VIN and VBAT?

I ask because I'm planning to make very simple devices that other people in my office will be using, frequently when I'm not there to remind them to connect batteries in the correct polarity. And despite all the physical obstacles that one could introduce (e.g. tabs on the battery holder), I'm sure someone will find a way to reverse + and -. I just want to know if doing so will fry the Teensy and require me to add protection circuitry or if I'm OK as is.
 
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The diodes on VBAT allow the 3.3 volt power to automatically power the VBAT pin, but the battery provides power as soon as the normal voltage drops lower than the battery voltage (presumably a 3.0 volt coin cell). When the coin cell is powering the real time clock (VBAT pin), current can't flow back into the main 3.3 volts because of the other diode. Likewise, the 3.3 volts can't attempt to charge the coin cell when the battery's voltage is less than 3.3 volts.

Yes, the diodes do protect against reverse polarity. It's safe to connect a battery that may be installed backwards to VIN or VBAT.

But it is not safe to allow reverse polarity when connecting directly to 3.3 volts. If you try to power the whole board that way, for example using a pair of AA or AAA batteries between 3.3V and ground, you must use battery holders that mechanically prevent reverse polarity connection. Here's one:

http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=BHAA-POL-ND
 
One wish - it looks like PTA0 ... PTA3 are completely masked behind the Mini54. Is there any way to expose them to the outside world for external ARM-JTAG or ARM-SWD programming? (using some fine soldering work perhaps?). Would the Mini54 withstand this type of treatment? :)
 
PaulStoffregen said:
The diodes on VBAT allow the 3.3 volt power to automatically power the VBAT pin, but the battery provides power as soon as the normal voltage drops lower than the battery voltage (presumably a 3.0 volt coin cell). When the coin cell is powering the real time clock (VBAT pin), current can't flow back into the main 3.3 volts because of the other diode. Likewise, the 3.3 volts can't attempt to charge the coin cell when the battery's voltage is less than 3.3 volts.

Yes, the diodes do protect against reverse polarity. It's safe to connect a battery that may be installed backwards to VIN or VBAT.

But it is not safe to allow reverse polarity when connecting directly to 3.3 volts. If you try to power the whole board that way, for example using a pair of AA or AAA batteries between 3.3V and ground, you must use battery holders that mechanically prevent reverse polarity connection. Here's one:

http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=BHAA-POL-ND
Click to expand...

or add a diode in reverse across the battery inputs (e.g. 1N4001, 4002, 4004 etc -- any one will do) if using AAA, or 1N5401 (5402, etc.) if using AA. This will short the battery if it is connected in reverse, so the battery will run down, but the Teensy won't get damaged. Don't do this if you are using larger or rechargeable batteries as the current would be too high.
 
Hi, all-

Just ordered a Teensy 2.0 and a Teensy 3.0. They haven't arrived yet, but I am taking some time to prepare myself for their use (first-timer here)

My first question is about the 3.0. I looked at the schematic, and was wondering what the auxiliary processor (MINI54TAN) is for?
Also, is there any generally descriptive documentation that explains the overall design philosophy and features? I am wondering if I have missed a link somewhere.

Also, can the Arduino IDE "leonardo" setting be used for Teensy 2.0, or must I still use the Teensyduino add-on?

As far as my background goes, I am a very experienced ATMega328 user, in various guises- Arduino UNO, Adafruit Boarduino DC and various home-brew projects.

As a newcomer to the Teensy, I would appreciate any assistance!

Many thanks,
Daniel
 
EasternStarGeek said:
was wondering what the auxiliary processor (MINI54TAN) is for?
Click to expand...

In a nutshell, the Freescale ARM chip lacks a hardware bootloader feature. The other chip controls the boot process, so you get a very familiar development process. It also does this without consuming any flash memory on the main chip, so your program can use the whole memory.


Also, can the Arduino IDE "leonardo" setting be used for Teensy 2.0, or must I still use the Teensyduino add-on?
Click to expand...

That's not recommended. You can probably build .hex files that will work (File > Preferences to enable verbose info), and then open them with the Teensy Loader.

When you use the Teensyduino add-on, a Tools > USB Type menu is added with several USB options not available on Leonardo (MIDI, Joystick, etc). Teensyduino's USB virtual serial implementation is also much faster and more efficient than Leonardo's.
 
Reverse-polarity protection improvement

Jp3141 said:
or add a diode in reverse across the battery inputs (e.g. 1N4001, 4002, 4004 etc -- any one will do) if using AAA, or 1N5401 (5402, etc.) if using AA. This will short the battery if it is connected in reverse, so the battery will run down, but the Teensy won't get damaged. Don't do this if you are using larger or rechargeable batteries as the current would be too high.
Click to expand...

That's a technique I use frequently, but with two important enhancements:
1. I always put some kind of over-current protection (polyfuse, etc) in the feed to the circuit, ahead of the reverse diode, which eliminates a flame-out if a low-impedance power source is accidentally connected backwards.

2. Using a Zener in place of the 1N400x diode, oriented the same way (cathode to +) buys you over-voltage protection, in addition to reverse-polarity protection. Much more bang for the buck that way! Be sure you know how Zeners work, and pick a sensible breakdown voltage that ensures the diode won't turn on at your intended operating voltage!

That's what us old-timers used to call a "Crowbar" protection circuit.
 
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Adi Oltean said:
One wish - it looks like PTA0 ... PTA3 are completely masked behind the Mini54. Is there any way to expose them to the outside world for external ARM-JTAG or ARM-SWD programming? (using some fine soldering work perhaps?). Would the Mini54 withstand this type of treatment? :)
Click to expand...

Alternatively, since PTA0 .. PTA3 are all the JTAG pins, couldn't the Mini54 be made into a JTAG frontend?

Based entirely on how it's connected: Couldn't that be how the Mini54's programming the K20 anyway? *that* would be an awesome process to get a look inside.

I somewhat wonder if that's related to the following quote, from Paul:

Paul said:
Yes, halting mode is enabled. Currently it's only used for the auto-reset feature, but I plan to do much, much more in several months. I can't discuss those plans at this time.
Click to expand...

;)
 
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I second that bill of materials request. Would be great to have - I'm sitting here trying to figure out exactly what specs I should be using that PTC 'fuse,' and various other components...

(Sorry for reviving a dead thread)
 
Oh, I agree completely, Stevech. But I figured it couldn't hurt to ask. :D

I figure, I'm making my PCB with an integrated Teensy anyway (I'll be using Paul's pre-programmed MINI54's). If I can get a BOM, it makes my life a bit easier, and doesn't change the amount of money I'm giving to Paul for this project. On the other hand, I completely understand not wanting to give too much away, as someone with fewer scruples could then easily make their own Teensy clone/competitor.
 
MuShoo... sorry, I wasn't singling out anyone... just impressed at Teensy being so open, despite what goes on over there.
 
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