7. Advanced Energy Monitor
7.1 Usage
The AEM (Advanced Energy Monitor) data is collected by the board controller and can be displayed by the Energy Profiler, available
through Simplicity Studio. By using the Energy Profiler, current consumption and voltage can be measured and linked to the actual
code running on the EFM32 in realtime.
7.2 Theory of Operation
The Advanced Energy Monitor (AEM) circuitry on the board is capable of measuring current signals in the range of 0.1 µA to 95 mA,
which is a dynamic range of alomst 120 dB. This is accomplished through a combination of a highly capable current sense amplifier,
multiple gain stages and signal processing within the kit's board controller before the current sense signal is read by a host computer
for display and/or storage.
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.
The current signal is combined with the target processor's Program Counter (PC) sampling by utilizing a feature of the ARM CoreSight
debug architecture. The ITM (Instrumentation Trace Macrocell) block can be programmed to sample the MCU's PC at periodic intervals
(50 kHz) and output these over SWO pin ARM devices. When these two data streams are fused and correlated with the running appli-
cation's memory map, an accurate statistical profile can be built, that shows the energy profile of the running application in real-time.
At kit power-up or on a power-cycle, and automatic AEM calibration is performed. This calibration compensates for any offset errors in
the current sense amplifiers.
4.7R
Sense Resistor
LDO
3.3V
VMCU
Current Sense
Amplifier
AEM
Processing
Multiple Gain
Stages
EFM32
Peripherals
Power Select
Switch
5V
G
0
G
1
Figure 7.1. Advanced Energy Monitor
7.3 Secondary AEM Channel
The EFM32 Giant Gecko GG11 Starter Kit contains a secondary AEM channel in addition to the default one. This secondary channel
has a sense resistor on the USB VBUS line connected to the EFM32's USB regulator input, and allows energy monitoring of a bus
powered USB application, showcasing the EFM32 Giant Gecko GG11's low energy USB peripheral.
In order to use the secondary AEM channel, the power switch must be set to the "USB" position so that the EFM32 is configured as a
bus powered device with the internal USB LDO regulator powering the device's VDD rail. The board controller monitors the switch posi-
tion, and performs an automatic switch-over and calibration when the USB position is selected and a valid voltage is present on the
VBUS rail. Both the current and the voltage measurement will now show the VBUS supply instead of the normal 3.3 V supply.
Please note that the recalibration that occures when switching between the "USB" and "AEM" modes on the power switch causes the
target EFM32 to lose power for a few seconds.
UG287: EFM32 Giant Gecko GG11 Starter Kit User's Guide
Advanced Energy Monitor
silabs.com
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