Max current on header 5/3.3V supply

Hi everyone, I’m trying to figure out if it’s safe to power an xbee off the 3.3V header on the bbb ( P9_3 / P9_4 ) … I need 250ma-300ma MAX

is this safe and stable? It would seem like it, but I want to confirm… thank you!

When you read the service reference manual, section 8.6, you find that the VDD_3V3B at P9 pins 3 and 4 can source 250 mA max.

Those numbers are for each pin, so 500 mA total.

I doubt that. The pins are connected together. Also: VDD_3V3A Rail
The VDD_3V3A rail is supplied by the TPS65217C and provides the 3.3V for the
processor rails and can provide up to 400mA. VDD_3V3B Rail

The current supplied by the VDD_3V3A rail is not sufficient to power all of the 3.3V
rails on the board. So a second LDO is supplied, U4, a TL5209A, which sources the
VDD_3V3B rail. It is powered up just after the VDD_3V3A rail.

U4 is capable of sourcing 500 mA, but on-board it also powers nand, ethernet and uSD. Whatever is left for externals is less than 500 mA, 250 mA left as is documented seems reasonable.


thanks everyone, so I guess the answer is yes? xbee uses 215ma max, so it looks like it’s safe

If I tie the two 3.3V pins together, can I draw 0.333mA or just 250mA??

I’m using 3 thermistor sensors at 0.11mA each so I’m wondering if I’m going to blow my board.

Many thanks for some knowledgable input!!

Tying them together will not increase current capacity. They both come from the same place on the board, the power supply device itself…



I think you are confusing Amperes (A) and milliAmperes (mA).

You need to understand the difference and then re-run your calculations.

I doubt that three thermistors, each drawing a fraction of a milliAmpere would overload a 250 milliAmpere supply.

— Graham