Current loads?

(Dave) #1

When I start attaching my own circuits to the HiFive1’s power and I/O pins what kind of loads are safe to draw? I presume I’m good for up to ~500mA when powered from USB, minus the draw of the board components?

What about when I start powering from the barrel connector, how much can the on-board regulator handle before getting a bit toasty?

I don’t need precisely measured figures, mind, but something a little more quantified than my Grandfather’s method of “touch the regulator and measure the diameter of the resultant blister.” Thanks.

(Megan A. Wachs) #2

Your grandfather sounds like a smart guy :slight_smile:

You’re right about the 500mA USB limit.

Your limit for the on-board supplies is 15W when driving with the External power jack. This is the limit of the 5V regulator (U7), so you’ve got about 3A at 5V. This has to cover the HiFive1 components as well of course, whatever remains is good for your shields at 5V.

Also, U8, the 3.3V regulator, can only supply 1A. So if you try to supply 3.3V shields with that supply directly, you have that limit as well.

EDIT: I was wrong. Don’t do this! 5V supply is only as an output of HiFive1. There is of also the external 5V pin on the header, so if you have a regulated 5V DC supply hooked up to your giant LED display (for example), you could use that as the power supply for the HiFive1.

(Dave) #3

It may be a little more accurate to suggest he benefitted from a certain amount of domain-specific intuition. :grin:

Realistically, I don’t think I’ll actually draw that much (barring accidents), but has anybody tried testing that edge-case? I’m sure the part will oblige but dissipating a lot of heat which may not be good for the rest of the board, especially if there’s a shield on top limiting air-flow.

Thanks! Both very handy to know.

(Megan A. Wachs) #4

Please see edit above. The board designer corrected my earlier statement about the 5V supply.

Also he reminded me that you should be careful if using LCD displays with backlights, and don’t short their backlight power supply to the control logic supply. Basically check schematics and use your ohmmeter, and happy to discuss specific ideas/concerns on the forums!

(Donnie Agema) #5

Here are some technical trivia results of my testing:

The temperatures were measured using an LM335AZ pressed against the each chip case. The power drain measurements were made using DVM between USB cable +5v output and USB connector +5v input.

I find it interesting that the FT2232HL appears to dissapate about 2,5 times as much heat as the HiFive1 chip running at 265 MHz