RT1051 Booting up with only USB power

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RT1051 Booting up with only USB power

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Contributor I

Does anyone have experience with the RT1051 in a USB device application where all the power is supplied via USB? Will the device be able to get enough power to boot up and what is the power sequencing necessary for booting from USB power?

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Specialist V

Hi Gerry

The Teensy 4.0 is USB powered so I would look at its circuit diagram here: https://www.pjrc.com/teensy/schematic.html
(it uses the 1062 but I think its prototypes were with 1052 or 1051 so equivalent).


Regards

Mark
[uTasker project developer for Kinetis and i.MX RT]

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Contributor I

Thanks for the reply Mark.

The schematic you reference seems incomplete and seems to use a battery to power the VDD_SNVS_IN. It also uses a linear regulator for the main supply so I assume the circuit is fairly low current. Neither of these are options for the design I am working on.

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Specialist V

Gerry

I don't think that the diagram is incomplete since it is from a small board that has been used by a large community for some time (although it may only show actually connected processor pins) - VDD_SNVS_IN is supplied by the main 3.3V power when available and switches to an optional battery when not.
However it is not my design, just one from a board that I have used that is USB powered.
Of course whether it is suitable for particular applications is another question but it may give an idea. Since the USB/linear regulator is only supplying the processor in this circuit other current taken from the USB 5V line is not defined so I suppose that it is up to whatever is connected (see VIN) to manage that part.

Regards

Mark

[uTasker project developer for Kinetis and i.MX RT]

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Contributor I

After looking into this a bit, it seems like inrush current will be an issue. Looking at the EMV board, powering it from only USB would violate the USB inrush current specification. I would appreciate some feedback about how to deal with this from someone who has done a 105/1060 USB device implementation.

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