Anelok: MCU idle current down to 2.0-2.1 uA

Werner Almesberger werner at
Wed Jul 30 14:53:11 UTC 2014

Found the culprit: it was the USB voltage regulator that burned 500 uA
while idling. Turning it off brought current in LSS (low-leakage stop)
mode down to about 2.0-2.1 uA.

Before finding the high leakage of the voltage regulator, I had suspected
and removed the boost converter. So I'll have to put that one back later.
The system consisted basically just of the KL26 for these tests - the
CC2543 is not connected to power, all GPIOs are disabled (so the CC2543
does't get powered by leak currents either), and most of the other
components are still not placed.

LLS is the "nicest" low-power mode: the core sleeps, the 32.767 kHz
oscillator is running, capacitative sensing should still be possible (the
Touch Sense Input module can run autonomously, but I still have to get to
this) and the chip wakes up either from the low-power timer (LPTMR) or
from a low-leakage wakeup (LLW) interrupt.

In LLS, the core should draw some 1.7 uA at 25 C. The crystal oscillator
should add 490 nA, so 1.7 + 0.49 = 2.19 uA while measurements yield 2.0
to 2.1 uA. My office is a bit cooler than 25 C most of the time (it's
still winter here), which may explain the difference.

- Werner

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