Teensy 3.5: could withstand 6.4V Vin?

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XFer

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Hello everyone,

I have a battery-powered project based upon Teensy 3.5, for which a requirement is adoption of AA batteries.

Now, those may be either alkaline (1.6V when fresh, 1.0V when almost depleted) or NiMh (1.35V when fully charged, 0.8V when almost depleted).
So, wanting to extract the maximum juice from the batteries, I'm looking at a power source which may vary between 4x1.6V = 6.4V and 4x0.8V = 3.2V :(

I know from experience that 3.2V applied to Vin are still OK for powering the Teensy 3.5 (despite the 3.6V minimum advertised voltage); but what about 6.4V (fresh alkaline batteries)?
Is it absolutely too much to bear?

Of course I could lower the voltage with a diode, but then I would not extract all the juice from NiMh. :(
 
Hello everyone,

I have a battery-powered project based upon Teensy 3.5, for which a requirement is adoption of AA batteries.

Now, those may be either alkaline (1.6V when fresh, 1.0V when almost depleted) or NiMh (1.35V when fully charged, 0.8V when almost depleted).
So, wanting to extract the maximum juice from the batteries, I'm looking at a power source which may vary between 4x1.6V = 6.4V and 4x0.8V = 3.2V :(

I know from experience that 3.2V applied to Vin are still OK for powering the Teensy 3.5 (despite the 3.6V minimum advertised voltage); but what about 6.4V (fresh alkaline batteries)?
Is it absolutely too much to bear?

Of course I could lower the voltage with a diode, but then I would not extract all the juice from NiMh. :(

I use a T3.6 on 4 Alkaline D-cells. Assume, T3.5 is similar in this respect. (the 6V PJRC gives as limit for Vin has large margin)
 
First, you *must* cut the VUSB-VIN pads apart on the bottom side of the board, if you will ever plug the USB cable in while the battery is connected. Even if you believe you would never do this, I recommend cutting those apart anyway for safety. Damage to a PC by feeding the battery power back into your PC's USB power could really ruin your day. If you haven't recently backed up your code or other info, the possible loss of data adds insult to injury. Don't take that risk!

Only apply this battery power at the VIN pin, which powers the 3.3V regulator on the Teensy 3.5. If you accidentally touch 6V to the 3.3V power line, even for a brief moment, the board will be destroyed.

Higher than 6V power input is not as safe on Teensy 3.6, because VIN powers both the LP38691 regulator and the TPD3S014 USB power switch for the 2nd USB port. Teensy 3.5 does not have the TPD3S014. Details here.

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

The LP38691 is actually rated for up to 10 volts. But we recommend not more than 6V because the LP38691 can overheat if you also use near the maximum 250 mA from the 3.3V power line. Usually this isn't an issue if you have not connected other stuff to the 3.3V power. Still, it's a good idea to check the temperature of that part while testing your project while running from fresh batteries.
 
Excellent, thanks! Great infos as always. :)

Yes I already have the habit of cutting VUSB-VIN as a safety measure (better safe than sorry). :)
 
Higher than 6V power input is not as safe on Teensy 3.6, because VIN powers both the LP38691 regulator and the TPD3S014 USB power switch for the 2nd USB port. Teensy 3.5 does not have the TPD3S014. Details here.

OK, I see that TPD3S014 is only rated up to 6V.
I never used or plan to use 2nd USB port.
Question is now: should I remove TPD3S014 if I wanted to apply say 2S lithium batteries on Vin, or is 6V rating for operating conditions (i.e. using 2nd USB)?
 
You could also add a buck-boost converter between the battery and the Teensy, so that you have always stable 5V for input voltages from 3 to 12V: https://www.adafruit.com/product/2190

I was using similar in the past (to 6V as I need 5V for Analog circuitry). However space is now premium and also additional consumption of voltage converter is an issue.
But I may return to initial convert to 6V solution or get 3.0V AA size Li batteries.
 
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