Prop max current. Just want to make sure I'm right

TC

Hello all.

I am figuring out how much current my project requires, so I can order a power supply for it. I am basing my power supply off the max current for everything. I figure, doing it that way would give me a buffer zone, and I should never need the max current.

Looking at the prop datasheet (page 25, table 18), under "Absolute Maximum Ratings" I am seeing Max. current into Vdd pins is 300mA. Is that the max current the prop would ever need? Or could it be higher?

Thanks
TC

Bean

300mA is the maximum without damaging the Propeller chip.

The current depends on the Propeller clock speed, how many cogs are running, what the running cogs are doing, and whatever you are driving with the pins.

Bean

TC

Bean wrote: »

300mA is the maximum without damaging the Propeller chip.

The current depends on the Propeller clock speed, how many cogs are running, what the running cogs are doing, and whatever you are driving with the pins.

Bean

Wonderful, Thank you.

Duane C. Johnson

Hi TC;

As Bean said 300mA is the maximum current on the Prop's power pins.
However, the Prop itself consumes no where near 300mA. Its the stuff connected to it that cause the high currents.

Others probably have a better idea of what the Prop running current is at max clock speed, or even over clocked, and all 8 cogs running without any loads.
After knowing the max Prop running current it should be easy to add up all the load currents in a system.

BTW, prudent design would suggest that one should never operate at these max ratings.
Maybe 50% or 75% would be a better choice.
Say, 200mA on the power pins and 20mA on the I/O pins.

Duane J

TC

Duane C. Johnson wrote: »

Hi TC;
BTW, prudent design would suggest that one should never operate at these max ratings.
Maybe 50% or 75% would be a better choice.
Say, 200mA on the power pins and 20mA on the I/O pins.

I completely agree. I am not planing on using that much current, I just want to account for worse case scenario, that will never happen. I am only using 10 I/O pins, 2 of them will have LED's on them, the rest is just data and 5 have 10K pull-ups.

LoopyByteloose

I try to target all my i/o pins for 1 or 2 ma, and 5ma at max.

Just about everyone drives LEDs directly and at high milliamps, but it isn't really the best solution for a durable design. I often wonder why people desire their LEDs to be so bright.

I strongly believe that the Propeller should be the source of control, NOT the source of power.

tomcrawford

There are some curves on page 26 of the data sheet that might help.

Phil Pilgrim (PhiPi)

Loopy Byteloose wrote:

I strongly believe that the Propeller should be the source of control, NOT the source of power.

The Prop's output drivers are actually quite robust. Just to drive a 75-ohm NTSC monitor (a common Propeller app) requires about 14 mA from one of the video out pins.

-Phil

LoopyByteloose

I certainly can appreciate that in that context, higher output is necessary.

But the problem is when users begin to think every pin can drive 14ma all at the same time.