3.3v pins on 3.2 and eagle components

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alialiali

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Hi!

On the teensy 3.2 (which I read has a more powerful voltage regulator which I need for an esp8266-01) the side 3.3v pin has limited current, but the back 3.3v pin has more. In prototyping I use the back pin and it is all fine. The Teensy 3.1 eagle components I have seen mostly* connect the two 3.3v which I guess is wrong? Is it safe to connect them?

*The SparkFun component has separate pins as "3v" side pin, and "3.3v" back pin which I guess is correct.

Thanks!
 
I didn't look at SparkFun - but there are three 3.3V points on my Teensy 3.2 and 3.1 and all are common. There is only one source of 3.3V on the Teensy.

My ESP8266 units were connected on the T_3.2 button end 3.3V pin and worked fine.
 
alialiali said:
The Teensy 3.1 eagle components I have seen mostly* connect the two 3.3v which I guess is wrong? Is it safe to connect them?
Click to expand...

Yes, it's safe and you should in fact connect the two 3.3V pins on your PCB. But using only one of them also works fine, if it's inconvenient to connect both. The one next to pin 23 is preferable.

*The SparkFun component has separate pins as "3v" side pin, and "3.3v" back pin which I guess is correct.
Click to expand...

Sparkfun's info is wrong. I've sent many requests to them to update that product. The discrepancy in labeling one pin "3.3V" and the other "3V" is just one of many issues.

alialiali said:
Great info, thanks. What got me confused is the pin out says 250mA max on the 3.3v pin next to 23.
Click to expand...

The 250 mA max is a recommendation based on heating of the voltage regulator chip if you run from 6V input. The chip is actually rated for 500 mA and up to 10V input, but with the PCB-only heat dissipation you can't use the whole range before the chip overheats. 250 mA might be a bit on the conservative side...
 
PaulStoffregen said:
The 250 mA max is a recommendation based on heating of the voltage regulator chip if you run from 6V input. The chip is actually rated for 500 mA and up to 10V input, but with the PCB-only heat dissipation you can't use the whole range before the chip overheats. 250 mA might be a bit on the conservative side...
Click to expand...

The numbers Paul provides here mean that the regulator has to dissipate (6-3.3)V * 0.25A = 0.675W. If you run the Teensy from USB power the input voltage will only be 5.25V maximum (according to USB spec). If we keep the allowed power dissipation at 0.675W and plug 5.25V into above formula the allowed current is 0.675W / (5.25-3.3)V = 0.346A. So even with Paul's conservative power rating you could drive two ESP8266 modules, continuously Tx/Rx-ing, from a single Teensy3.2.
 
Ben said:
The numbers Paul provides here mean that the regulator has to dissipate (6-3.3)V * 0.25A = 0.675W. If you run the Teensy from USB power the input voltage will only be 5.25V maximum (according to USB spec). If we keep the allowed power dissipation at 0.675W and plug 5.25V into above formula the allowed current is 0.675W / (5.25-3.3)V = 0.346A. So even with Paul's conservative power rating you could drive two ESP8266 modules, continuously Tx/Rx-ing, from a single Teensy3.2.
Click to expand...

Awesome, thank-you.
 
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