8.2 AEM Theory of Operation
In order to be able to accurately measure current ranging from 0.1 µA to 50 mA (114 dB 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 250 µA. Digital filtering and averaging is done within the Board Controller before the samples are exported to the
Energy 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.
8
Figure 8.2. Advanced Energy Monitor
8.3 AEM Accuracy and Performance
The AEM is capable of measuring currents in the range of 0.1 µA to 50 mA. For currents above 250 µA, the AEM is accurate within 0.1
mA. When measuring currents below 250 µA, the accuracy increases to 1 µA. Even though the absolute accuracy is 1 µA in the sub
250 µA range, the AEM is able to detect changes in the current consumption as small as 100 nA. The AEM produces 6250 current
samples per second.
Note:
The current measurement will only be correct when powering the EFM8 from USB power through the debugger (power select
switch set to DBG or AEM).
UG238: EFM8SB2-SLSTK2011A User's Guide
Advanced Energy Monitor
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