If you want to reduce the power consumption of the MCU, it is common to design the software so that it operates intermittently. Intermittent operation refers to a series of processes such as shifting to sleep mode when necessary processing is completed, periodically returning to operating mode (waking up) to perform processing, and then shifting to sleep mode again after processing is completed. It works. By remaining in sleep, deep sleep, or standby modes with low power consumption during periods when the MCU is not processing, the average power consumption can be reduced.

Current consumption in sleep mode is called sleep current, and current consumption in standby mode is called standby current. The name differs for each MCU manufacturer. By using an MCU with excellent specifications (low current consumption), the average power consumption can be reduced.

Then, should we choose an MCU with excellent specs? Well, it's not that simple.
The expected behavior of the MCU in low power consumption mode depends on the design specifications of the device. For example, use a timer to autonomously wake up after a certain period of time. It waits while waiting for an external interrupt, and wakes up when a signal comes in. Alternatively, it is possible to monitor the sensor output with a comparator and wake up when it exceeds the threshold.
It is desirable for MCUs to have multiple low power consumption modes so that the optimum mode can be selected according to the application, but recently more and more products support multiple low power consumption modes. However, the name of the low power consumption mode is different for each manufacturer, and even if the name is the same, there are many differences in what can be done in that mode, so be careful when comparing. It is important to compare the current consumption values of the optimal power modes in light of the design specifications you want to achieve.
The EFM32 has four low power consumption modes from EM1 to EM4. In addition, since operating limits are set in detail for each peripheral, the optimum power consumption mode can be selected to reduce power consumption.

Sleep/standby current is a very important spec when the CPU is awake and doing work for very short periods of time, while staying in sleep/standby mode for long periods of time.
Conversely, if the operating mode ratio is high, the active current will dominate over the sleep/standby current.