Digital Output Pin high Voltage tolerance

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HI,

For my Project I want my Teensy to be able to switch the power off completely (switched on again by a button press). For this I am using the Enable pin of a buck converter which goes high when the user presses the button and then powers the teensy. As soon as the teensy is started it sets the connected pin to high an the power stays on:

Schema.PNG

I have used this before with an input voltage of only 4.2v. Now I want to use it with up to 12v and I am wondering if the Teensy will survive the button press (and therefore 12v on its pin). I assume that this is not a good idea. What would be an easy way to protect the Teensy Pin?
Would a series diode in front of the pin help?

The enable pin of the converter requires only 1v or so to be high.

Thakns for your help
Meini
 
Try putting another resistor in series with the switch to form a voltage divider. A 270k resistor will put the pin at 100k/(270k+100k)*12 or about 3.24v.
 
Sorry, for not mentioning that earlier, but the supply voltage can vary from 4 to 12 volts. Thats why a voltage divider does not work well (it might just work for 4v as well, if I use exactly the right values, but it seems a bit tight).
 
oh, yes, I didn't think about that configuration. That would mean a Zener parallel to the pull down resistor and current limiting resistor between 12v (or the switch) and the zener?

But I am still curious about a (normal) diode between the teensy pin and the 12v supply. Wouldn't that prevent current flowing into the pin because of overvoltage and prevent damage? Or am I missing something here?

Thanks a lot for all the help.
 
Not sure about your question about "diode between 12v and Teensy": could you draw a schematic?

Also, are you sure that 12v on the EN pin of the buck converter is OK? It may not accept such a high logic level.
 
Also, are you sure that 12v on the EN pin of the buck converter is OK? It may not accept such a high logic level.
Yes, because, usually the EN pin is just tied to VIN of the Buck Converter (according to the typical application in the datasheet).

Schematic of the Diode in between pin and EN:
SchemaDiode.PNG
 
Mmm.
That diode would pretty much cut the teensy out of the circuit. I don't think this is what you want.

On second thought, I'm not so sure a zener is ideal.
Usually one could do with a level shifter, but I don't know of level shifters with such large a range.
An optoisolator should do.
 
hat diode would pretty much cut the teensy out of the circuit. I don't think this is what you want.
wouldn't it only do that if the switch is closed? if so that would be perfectly fine. As long as the switch is closed, the EN pin is high anyway. only when the switch is open i want teensy to be able to control the EN pin.
 
Ah, sorry, missed that. So the switch is meant to override Teensy control of the buck converter.
Should do.
 
yeah, basically this is a "soft power button". when the user presses the button the converter will start up and power the teensy. From that moment onwards (after the user releases the button again) the teensy will controll the EN pin. After a certain idle time the teensy will pull the EN pin low again an the converter will power down until the user presses the button again.
 
Ok. The diode shoud work, I would still add a series resistor as a current limiter, let's say 1K.
 
Without testing and guarantee I'd say something like that should work? D1 ~3V, choose R1 small enough that sufficient current flows to keep the diode in brake down mode (read datasheet). R2 can be rather high since you don't need to override the switch.

diode.PNG
 
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