T3 Power and protection questions
I just cut and paste the two emails I sent to Paul before this forum board got started.
I thought it would be helpful to post this Q/A on the forum board for other users.
Here is Paul's replies from two emails. Hope you don't mind Paul.
Yes.
Maybe. It's certainly not good for the hardware to do this. But often the stress does not actually result in permanent damage.
Yes, 9 ma is the recommended maximum.
Yes.
Yes, there's a schottky diode between VIN and the regulator input.
The Teensy 3.0 would probably survive, but this would short the USB power to your power supply. One will likely drive current into the other, which isn't good. If they're both very close to 5.0 volts, hopefully it won't be a terribly destructive event.
I just cut and paste the two emails I sent to Paul before this forum board got started.
I thought it would be helpful to post this Q/A on the forum board for other users.
Here is Paul's replies from two emails. Hope you don't mind Paul.
#1. Current draw of Teensy 3 with nothing connected except USB?
Someplace I read ~ 27 mA.
Yes.
#2. If an output pin gets "direct" shorted to ground, you will probably lose the pin on the K20 ?
If one pin is an output [High] and another pin is an output [Low] and both pins are shorted together -- you probably will lose some pins?
Maybe. It's certainly not good for the hardware to do this. But often the stress does not actually result in permanent damage.
#3. What series limiting resistor would you recommend to prevent all the current going to ground on a direct short and still have
some usable output drive current?
3.3 v / 5 ma. = 660 ohms? (Using K20 9 ma. max.) <--- my guess.
Yes, 9 ma is the recommended maximum.
#4. Does the Teensy 3 has only one input VIN regulator on the T3 module?
Yes.
#5. On the Teensy 3, is there input reverse polarity protection on the VIN input ? (with the on-board VIN bridge pads "cut")
Yes, there's a schottky diode between VIN and the regulator input.
It should be fine.#6. Will you destroy the Teensy 3 with polarity reversal on Teensy 3 VIN and ground?
Yes. The regulator is specified for 120 mA.#7. The 3.3 VDC out has a max. 100 ma. Does the K20 idle current of 27 ma. "eat into" (subtracts from) this max current output?
The max. power current for "all" K20 I/O pins is 100 ma. by Freescale specs. Question 4 is related to this question.
#8. What will happen, if you have the VIN jumper in, and power the Teensy 3 with USB power and VIN power at the same time?
The Teensy 3.0 would probably survive, but this would short the USB power to your power supply. One will likely drive current into the other, which isn't good. If they're both very close to 5.0 volts, hopefully it won't be a terribly destructive event.