[Noisebridge-discuss] [dorkbotsf-blabber] MCU > 80MHz, low pincount, power saving?

aws andy.schmeder at gmail.com
Sat Nov 12 21:05:35 UTC 2011

Nice try, no you can't just cancel out the currents. :)  As I understand it the issue is buildup of heat generated by the gates, which are in the best case 90% efficient, the other 10%+ of the power going past the gate has to be dissipated into the air otherwise it will eventually wear down the circuitry and prematurely destroy the chip. Those plastic IC packages have a relatively high thermal resistance.

That said I have exceeded the limits by quite a lot on some projects, but those were prototypes, not products intended to have a multi-year operating lifespan.


> Right. I have a ST Micro Cortex-M4 (same core as the Kinetis K60
> posted above). The data sheet says each GPIO can source or sink +/-
> 20mA. It also refers to a limits table which says any individual I/O
> pin can source or sink up to 25mA, while the sum of all currents must
> be within +/- 25mA. I wonder if that means you can drive two 25mA
> lines as long as you also sink two? It was a free eval board if you
> want to try to break it.
> http://www.st.com/internet/evalboard/product/252419.jsp?WT.ac=p2_bn_sep11_stm32f4discovery

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