Iris Carier board Limited Power USB

Technical Support
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1

The standards of our application refer to IEC60950-1, and one of those referrals involves the use of Limited Power Sources. It states that Limited Power Source need to be used, for then the electrician’s job is simplified, even if there is a (single) fault inside of the power supply.
Some examples of testing that a notified body might do, to determine the maximum output current and power meet the “Limited Power Source” requirements are:

Check the power supply at maximum rated load
Increase the load of the power supply until it is on the verge of overload
Simulate an internal fault by shorting the current-limiting resistor
Short out the opto-coupler that provides feedback to the control loop

Does the USB output of the Iris board comply with these requirements (limited power even if single fault occurs)?

Thanks in advance.

2

Dear @maw,

thank you very much for using the Toradex Developer Community.

The USB interface is powered by the standard power Distribution IC TPS2042BD from TI. Here the datasheet of the device:

I would like also to mention that you can easily download the iris pfd schematics or Altium product from our developer website:

I hope this helps. Please don’t hesitate to get back to us if you need further help.

3

Thanks, @diego.tx
This is in fact the source of my concern: If the TPS2042 fails for some reason, then the power source is not limited anymore. Is there any precaution implemented to deal with that?

4

Dear @maw,

in the unlikely event in which TPS2042 fails and still deliver the full current provided on the 5V power rails, this current will be limited to 3.5A.

At this point, the DC/DC overcurrent protection will kick in. This is the only precaution implemented on the Iris carrier board.

I hope this fits your requirements.