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2012-05-31 - t0014_0.11
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6 Advanced Energy Monitor
6.1 Usage
The AEM (Advanced Energy Monitor) data is collected by the board controller and can be displayed
by the energyAware Profiler, available through Simplicity Studio. By using the energyAware Profiler,
current consumption and voltage can be measured and linked to the actual code running on the EFM32
in realtime.
6.2 AEM theory of operation
In order to be able to accurately measure current ranging from 0.1uA to 50mA (114dB dynamic range), a
current sense amplifier is utilized together with a dual gain stage. The current sense amplifier measures
the voltage drop over a small series resistor, and the gain stage further amplifies this voltage with two
different gain settings to obtain two current ranges. The transition between these two ranges occurs
around 250uA. Digital filtering and averaging is done within the Board Controller before the samples are
exported to the energyAware Profiler application.
During startup of the kit, an automatic calibration of the AEM is performed. This calibration compensates
for the offset error in the sense amplifiers.
Figure 6.1. Advanced Energy Monitor
4.7R
Sense Resist or
LDO
3.3V
VMCU
Current Sense
Am plifier
AEM
Processing
Dual Gain
St age
EFM32
Sensors &
Peripherals
Pow er Select
Sw it ch
5V
HG
LG
6.3 AEM accuracy and performance
The Advanced Energy Monitor is capable of measuring currents in the range of 0.1uA to 50mA. For
currents above 250uA, the AEM is accurate within 0.1mA. When measuring currents below 250uA, the
accuracy increases to 1uA. Even though the absolute accuracy is 1uA in the sub 250uA range, the
AEM is able to detect changes in the current consumption as small as 100nA. The AEM produces 6250
current samples per second.
Note
The current measurement will only be correct when powering the EFM32 from USB power
through the debugger (power select switch set to "DBG").
Summary of Contents for EFM32 Giant Gecko Starter Kit
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