# Teensy 4.0 and 4.1 I/O Pin Current - Spec Conflict

#### SidInNJ

##### Member
According to the "Teensy Technical Specifications" web page (www.pjrc.com/teensy/techspecs.html), the current output per "Breadboard I/O" pin is 10mA, but the Teensy 4.0 page (www.pjrc.com/store/teensy40.html) says "The recommended maximum output current is 4mA". The datasheet at www.nxp.com/docs/en/data-sheet/IMXRT1060XXEC.pdf doesn't list the usual absolute maximum current for the I/O pins. Table 22 on page 33 says a "typical" value is 4mA, but with a voltage drop from VDDE of 0.45V.
Unfortunately, I based a design on the former web page and didn't notice the lower current on the latter 4.0 page. A Teensy 4.0 is driving a solid state relay using pin 3. The relay is drawing about 8mA and the drop from VDDE is only 0.124V. I'm hoping that tiny voltage drop is an indication that the circuit is sound. I've got about nine of them installed 300 miles away.

Anybody have any long term experience using greater than 4mA from an I/O pin on a 4.0? @Paul?

Thanks!
Sid

I am using Teensy 4.1 with solid state relays (7 of them).Here is the datasheet. I tried one of the relays with power supply aside from Teensy just to see how much current it draws. If I give 3.3 VDC from my power supply to the relay, it pulls 400 mA. So, I put a 1K resistor between Teensy 4.1 digital pin to the input of the relay to limit the input current so it will be less than 4mA. On the load side, I am running a 12 VDC fan with 8A. I realized that the fan is not running full speed. I think the relay is limiting the current going to the fan. Instead of 1K. I am thinking to use 330 ohm resistor so the relay can supply more current and I can increase the fan speed. But, in this case, the input current to relay that is drawn from Teensy 4.1's I/O pin will be 10 mA. So, my question is that can we comfortably draw 10 mA from any of the Teensy 4.1 digital I/O pins? The "specification table" in the website says that the "current output" is 10 mA, however, if you scroll down, it says "recommended current output" is 4 mA.

Appreciate the help.
Thank you,
Dervis

Driving the input with 3.3V directly and no series resistor would have damaged the IR emitter in the device - 400mA is four times the absolute maximum rating.
Thus the device is quite possibly not performing according to the datasheet any more.

The datasheet implies 10mA is a reasonable level to drive into it, with 1.4V Vf and 3.3V supply a total resistance of 190 ohms is needed, and the Teensy 4 output will already have maybe 50 or more ohms of internal resistance, so perhaps 150 ohm resistor makes sense.

In order not to overload the T4 output pin you could use double up with two output pins, each with 330 ohms, to drive the SSR. Having independent resistors protects the pins with damaging each other if not switched simultaneously.

Hi Mark,
Thank you very much for your reply. It really makes sense. Great solution.
One more question that I couldn't find neither in chip's datasheet nor Teensy's website: is there a limit of how much total current we can draw from all the I/O pins of Teensy 4.1? Based on what you said above, it seems like it is okay to pull 10 mA from an individual I/O pin of Teensy 4.1. I know there are 55 pins, does that mean I can draw 55 x 0.010 A = 0.55A from Teensy 4.1 with no problem? I am wondering what is the total current output from all the I/O pins?
Thank you again for the genius solution.
Dervis

From the Pinout Card, the max current draw is 250mA. So you can draw up to 10mA per pin, but not from all pins simultaneously. And preferably, you would draw 4mA or less from each pin.

From the Pinout Card, the max current draw is 250mA. So you can draw up to 10mA per pin, but not from all pins simultaneously. And preferably, you would draw 4mA or less from each pin.
That is not what the "250ma max" is referring to. It means you can tap 250ma max from the 3.3V supply pin to power other devices besides the Teensy.